field experiments on erosion by overland flow and their implication for a digital terrain model of channel initiation dietrich et al 1992 1993 proposed a digital terrain model for predicting the location of channel heads on the basis of the assumption that they occur where saturation overland flow exerts a boundary shear stress in excess of a critical value flume experiments were conducted in the modeled field site to evaluate the threshold hypothesis and to constrain critical shear stress and flow resistance parameters under complete grass cover microtopography and grass stems were found to prevent significant sediment transport at all but the highest flows when the grass stems were cut close to the ground flow resistance and critical shear stress for significant sediment transport were reduced by up to an order of magnitude but the remaining dense root mat prevented deep scour these field experiments support the threshold assumption and the model estimations of the critical shear stress if local topographic convergence of flow is taken into account the experiments also support the interpretation that significant degradation of vegetation cover is required for channel incision

embedding reach scale fluvial dynamics within the caesar cellular automaton landscape evolution model abstract we introduce a new computational model designed to simulate and investigate reach scale alluvial dynamics within a landscape evolution model the model is based on the cellular automaton concept whereby the continued iteration of a series of local process rules governs the behaviour of the entire system the model is a modified version of the caesar landscape evolution model which applies a suite of physically based rules to simulate the entrainment transport and deposition of sediments the caesar model has been altered to improve the representation of hydraulic and geomorphic processes in an alluvial environment in channel and overbank flow sediment entrainment and deposition suspended load and bed load transport lateral erosion and bank failure have all been represented as local cellular automaton rules although these rules are relatively simple and straightforward their combined and repeatedly iterated effect is such that complex non linear geomorphological response can be simulated within the model examples of such larger scale emergent responses include channel incision and aggradation terrace formation channel migration and river meandering formation of meander cutoffs and transitions between braided and single thread channel patterns in the current study the model is illustrated on a reach of the river teifi near lampeter wales uk

electrical conductivity of the continental crust geophysical measurements indicate that the earth s continental lower crust has a high electrical conductivity for which no simple cause has been found explanation usually relies on either saline fluids saturating the pores or interconnected highly conducting minerals such as graphite fe ti oxides and sulphides providing conducting pathways attempts in the laboratory to clarify the problem have hitherto been unable to recreate conditions likely to be present at depth by controlling the confining pressure and pore fluid pressure applied to a rock saturated with saline fluids at temperatures between 270 c and 1000 c here we report conductivity data obtained using a cell designed to make such measurements on rocks saturated with saline fluids our results show that the conductivity of saturated samples of acidic rocks is explicable entirely in terms of conduction through the pore fluid whereas the conductivity of saturated basic rocks requires the presence of an additional conduction mechanism s we have used the experimental data to construct electrical conductivity depth profiles for the continental crust which when compared with profiles obtained from magnetotelluric observations demonstrate that a mid to lower crust composed of amphibolite saturated with 0 5 m nacl shows electrical conductivities sufficient to explain conductivity depth profiles for the continental crust inferred from geophysical measurements

a numerical study on convergence of alongshore flows over the texas louisiana shelf 1 a hydrodynamic model is used to investigate convergent alongshore flows over the texas louisiana shelf characterized by down coast flows over the northern shelf encountering up coast flows over the southern shelf the model s ability to reproduce realistic current salinity and surface elevation fields is demonstrated through positive model skill scores when comparing model simulations to observational data the convergent flows are explored on both weather band and seasonal time scales for weather band scales this study focuses on wintertime convergent events the model predicted locations of convergent flows are supported by current measurements we find that the formation of convergent flows is primarily caused by along coast variation in the alongshore component of wind forcing which in turn is due to the curvature of the texas louisiana coastline in general the alongshore currents are well correlated with alongshore winds however the convergence points of currents and winds are not colocated but rather convergence points in ocean currents typically occur down coast of convergence points in the wind this offset is demonstrated to be mainly caused by buoyancy forcing that can drive the convergence location in the currents farther down coast no specific temporal pattern is found for the weather band convergence locations whereas at seasonal time scales the monthly mean convergence exhibits a prominent seasonal pattern with up coast migration of convergence locations in spring and summer and down coast migration in fall and winter

magnetic and electric fields associated with changes in high pore pressure in fault zones application to the loma prieta ulf emissions we determined the electric and magnetic fields generated during failure of faults containing sealed compartments with pore pressures ranging from hydrostatic to lithostatic levels exhumed fault studies and strain measurement data limit the possible size of these compartments to less than 1 km in extent rupture of seals between compartments produces rapid pore pressure changes and fluid flow and may create fractures that propagate away from the high pressure compartment along the fault face nonuniform fluid flow results from pressure decrease in the fracture from crack generated dilatancy partial blockage by silica deposition and clearing as pressure increases a direct consequence of this unsteady fluid flow may be associated transient magnetic signals caused by electrokinetic piezomagnetic and magnetohydrodynamic effects models of these processes for fault geometries with 1 km high pressure compartments show that electrokinetic effects are several orders of magnitude larger than the other mechanisms the electrokinetic signals produced by this unsteady flow are comparable in magnitude and frequency to the magnetic signals observed prior to the ml 7 1 loma prieta earthquake of october 18 1989 provided fracture lengths are less than 200 m

frictional melt pulses during a 1 1 ma earthquake along the alpine fault new zealand our understanding of frictional melting that occurs during large earthquake slip events has been hampered by the extremely fine grain size of frictionally fused rock and the lack of detailed high resolution microscopy studies that describe features at the crystal lattice scale in such a study we here report the complex nature of melting and crystallization in a symmetrically layered pseudotachylyte vein from the alpine fault new zealand two melt pulses are recognized attributed to successive but rapid injections of frictionally generated material the initial injection preserved at the vein margins was proximally derived and contains a high concentration of clasts and a si rich glass this was quickly followed by a second generation of a more distally derived melt dominated fraction which was injected into the weak vein center whereas fragments of wall rock biotite are preserved in the marginal zones neocrystallized microlitic biotite characterizes both margins and center the vein biotite is different in composition microstructure and polytypism from the metamorphic biotite of the wall rock in all melt layers newly formed biotite shows notable signs of syn flow crystallization strain features and erosion at crystal glass contacts with breakdown of neocrystallized microlites along both crystal edges and faces these characteristics imply cyclic pulses of heating melting and crystallization occurred during a single large earthquake episode and probably reflects the stick slip propagation properties of coseismic faulting 40 ar 39 ar total gas ages from the vein center give a 1 11 0 04 ma date for cyclic melting which based on current exhumation rates occurred at a crustal of depth v11 km 2003 elsevier science b v all rights reserved

spatial scale analysis of hydrographic data over the texas louisiana continental shelf on the basis of hydrographic data collected by the texas louisiana shelf circulation and transport processes study latex a and on earlier cruises we examined the energetic scales of spatial variability over the texas louisiana continental shelf shelf scale spatial reference fields were sought to represent the general distributions of circulation and water properties over the shelf at the time of the observations various methods were explored for determining such reference fields of potential temperature salinity and geopotential anomaly at the sea surface relative to 70 db spatial reference fields obtained from mean may fields and from polynomials fitted to individual may cruise data were compared on the basis of those comparisons quadratics were selected to fit property distributions from individual cruises and so to yield reference fields smaller scale anomaly fields were obtained by removing the reference fields from the observed distributions calculation of correlation versus separation distance based on these anomaly fields then allowed estimation of spatial scales of anomaly fields for cross shelf and along shelf transects the zero crossing scale and the gaussian decay scale are shown to be essentially the same and the zero crossing scale is used the principal results for the anomaly scales are 1 cross shelf scales over the western shelf are shorter order 15 km than those in the eastern and central regions order 20 km 2 along shelf spatial scales are of the order of 35 km 3 there is no significant difference in cross shelf scales at the surface middepth and bottom and 4 along shelf scales are essentially the same over the western and eastern regions of the shelf over the midshelf 50 m isobath and along the shelf break 200 m isobath and at different depths along the 200 m isobath the same spatial scales are found when using data with spatial resolution of 1 10 km cross shelf and 10 20 along shelf to obtain the anomaly fields so the data resolution used is adequate to represent the scales the variances of the observed shelf wide salinity temperature and geopotential anomaly are greater cross shelf than along shelf the variance of the cross shelf anomaly fields is around 10 of the shelf wide fields that of the along shelf anomaly fields is about 35 of that in the shelf wide fields the analysis of scales when grouped by season did not show persuasive evidence of seasonal variation

the effect of spatial heterogeneities on geomorphic expression in a model of basin evolution spatial variability is a basic component of all natural systems the system being studied here is the topography of an evolving drainage basin spatially heterogeneous erosivity within the drainage basin influences the structure of the drainage network the roughness of small scale features and the overall appearance of the simulated topography the presence of heterogeneities does not simply blur and smear analytical relationships the heterogeneities themselves introduce new structure to the organization of the drainage basin three measures the slope area relationship the cumulative area relationship and the hypsometric distribution are all systematically affected by spatial heterogeneity we will demonstrate how and why these relationships are affected and also how different structures in the heterogeneities themselves are manifested in the resulting simulated topography

the partitioning of the total sediment load of a river into suspended load and bedload a review of empirical data the partitioning of the total sediment load of a river into suspended load and bedload is an important problem in fluvial geomorphology sedimentation engineering and sedimentology bedload transport rates are notoriously hard to measure and at many sites only suspended load data are available often the bedload fraction is estimated with rule of thumb methods such as maddock s table which are inadequately field tested here the partitioning of sediment load for the pitzbach is discussed an austrian mountain stream for which high temporal resolution data on both bedload and suspended load are available the available data show large scatter on all scales the fraction of the total load transported in suspension may vary between zero and one at the pitzbach while its average decreases with rising discharge i e bedload transport is more important during floods existing data on short and long term partitioning is reviewed and an empirical equation to estimate bedload transport rates from measured suspended load transport rates is suggested the partitioning averaged over a flood can vary strongly from event to event similar variations may occur in the year to year averages using published simultaneous short term field measurements of bedload and suspended load transport rates maddock s table is reviewed and updated long term average partitioning could be a function of the catchment geology the fraction of the catchment covered by glaciers and the extent of forest but the available data are insufficient to draw final conclusions at a given drainage area scatter is large but the data show a minimal fraction of sediment transported in suspended load which increases with increasing drainage area and with decreasing rock strength for gravel bed rivers whereby in large catchments the bedload fraction is insignificant at 1 for sand bed rivers the bedload fraction may be substantial 30 50 even for large catchments however available data are scarce and of varying quality long term partitioning varies widely among catchments and the available data are currently not sufficient to effectively discriminate control parameters

on the response of a buoyant plume to downwelling favorable wind stress here the responseof a coastallytrappedbuoyantplume to downwelling favorablewind forcingis explored using a simplified two dimensional numerical model and a prognostic theory for the resulting width depth and density anomaly and along shelf transport of the plume consistent with the numerical simulations the analytical model shows that the wind causes mixing of the plume water and that the forced cross shelf circulation can also generate significant deepening and surface narrowing as well as increased along shelf transport the response is due to a combination of the purely advective process that leads to the steepeningof the isopycnals and the entrainment of ambient water into the plume the advective component depends on the initial plume geometry plumes that have a large fraction of their total width in contact with the bottom bottom trapped suffer relatively small depth and width changes compared to plumes that have a large fraction of their total width detached from the bottom surface trapped key theoretical parameters are wg wa theratioofthewidthoftheplumedetachedfromthebottomtothewidthoftheplumein contactwith it and the ratio of the wind generated mixed layer de to the initial plume depth hp which determines the amountofwaterinitiallyentrainedintotheplume themodelresultsalsoshowthatthecross shelfcirculation can be strongly influenced by the wind driven response in combination with the geostrophic shear of the plume the continuous entrainment into the plume as well as transient events is also discussed

momentum balances on the north carolina inner shelf four months of moored current pressure temperature conductivity wave and wind observations on the north carolina shelf indicate three dynamically distinct regions the surf zone the inner shelf between the surf zone and the 13 m isobath and the midshelf in the surf zone the along shelf momentum balance is between the cross shelf gradient of the wave radiation stress and the bottom stress the linear drag coefficient in the surf zone is about 10 times larger than seaward of the surf zone on the inner shelf the along shelf momentum balance is also frictional the along shelf wind stress and pressure gradient are balanced by bottom stress in the cross shelf momentum balance the pressure gradient is the superposition of roughly equal contributions from the coriolis force geostrophy and wave setdown from shoaling unbroken surface gravity waves at midshelf the along shelf momentum balance is less frictional and hence flow accelerations are important the cross shelf momentum balance is predominantly geostrophic because the greater depth and smaller bottom slope at midshelf reduce the importance of wave setdown the cross shelf density gradient is in thermal wind balance with the vertical shear in the along shelf flow in depths as shallow as 10 m the dominant along shelf momentum balances provide a simple estimate of the depth averaged along shelf current in terms of the measured forcing i e wind stress wave radiation stress divergence and along shelf pressure gradient that reproduces accurately the observed cross shelf variation of the depth averaged along shelf current between the surf zone and midshelf

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

experimental measurement of electromagnetic emissions possibly related to earthquakes in japan recent observations in the ussr appear to suggest that wide band electromagnetic radiation occurs just prior to earthquakes to apply this phenomenon to earthquake prediction measurements have been carried out at the sugadaira space radiowave observatory in japan under the ussr japan cooperation program in 1980 the recorded noise level at 81 khz is comparatively quiet throughout the day and night however about one half hour before the main shock of a magnitude 7 earthquake at 0733 ut on march 31 1980 the instrument recorded an anomalous amplitude increase to 15 db higher than the normal level vlf data recorded synoptically at sugadaira suggest that unusual impulsive radiation at frequencies below 1 5 khz also occurred shortly before the earthquake similar 81 khz emissions were observed prior to magnitude 5 and 6 earthquakes on september 25 1980 and january 28 1981

stable isotope and chemical systematics of pseudotachylyte and wall rock homestake shear zone colorado usa meteoric fluid or rock buffered conditions during coseismic fusion 1 a hydrous fluid phase is critical in controlling effective stress and fault mechanics and influencing the mineralogy and strength of materials within fault zones oxygen and hydrogen isotope and chemical analysis of wall rock gneiss pseudotachylyte and selected minerals in gneiss and pseudotachylyte from the homestake shear zone was used to assess whether melting occurred in the presence of meteoric water or involved only minor amounts of h2o derived from micas in wall rock gneiss bulk pseudotachylyte has slightly lower 18osmow than the whole rock protolith d for one bulk pseudotachylyte is essentially identical to biotite in gneiss d for two samples is lower by 20 bulk pseudotachylyte has lower sio2 and k2o and higher al2o3 feo mgo cao and h2o than gneiss the lower sio2 of pseudotachylyte compared to gneiss is explained by physical segregation of 25 to 72 volume of quartz clasts from the mobile melt phase samples of gneiss and pseudotachylyte define a sio2 18o mixing line between quartz and the most sio2 and 18o depleted pseudotachylyte physical segregation of quartz highest oxygen isotope composition in the pseudotachylyte gneiss system accounts for the slightly lower oxygen isotope composition of bulk pseudotachylyte relative to gneiss the similar d of pseudotachylyte and biotite from gneiss in one sample is consistent with dehydration melting of biotite during frictional heating and dissolution of biotite derived h2o in the melt late devitrification of glass and formation of greater amounts of fine grained muscovite accompanied by 10 30 loss of hydrogen as h2o results in lower d values in other samples in general melt generation occurred in a fault zone closed to infiltration of meteoric water there was no free h2o rich pore fluid present at the time of slip to potentially influence the behavior of the fault

wind modulated buoyancy circulation over the texas louisiana shelf this numerical investigation examines buoyancy driven circulation on the texas louisiana shelf modulated by seasonal winds in wintertime with downcoast in the direction of kelvin wave propagation wind forcing the mississippi atchafalaya river plume exhibits a bottom advected pattern the plume is fairly wide and the horizontal density gradients span almost across the entire shelf inshore of 50 m within the plume vertical shear of alongshore flow is in thermal wind balance with the cross shore density gradient and the shear causes a slight reversal of alongshore flow near the bottom an alongshore flow estimated by the thermal wind relation along with an assumption of zero bottom velocity generally well agrees with the actual flow near the surface in regions deeper than 20 m in spring and summer the thermal wind balance derived flow deviates from the actual alongshore flow and an ekman flow driven by strong onshore wind makes the major contribution to the deviation besides the summertime upcoast wind component transforms the plume to a surface advected state resulting in reduced cross shore density gradients and increasing the relative importance of wind driven barotropic alongshore flow which contributes to the remaining deviation

objectively mapped stream function fields on the texas louisiana shelf based on 32 months of moored current meter data on the basis of current measurements observed at 31 moorings during april 1992 through november 1994 as part of the texas louisiana shelf circulation and transport processes study we describe the horizontally nondivergent part of the near surface shelf wide scale low frequency circulation and its variability on the texas louisiana continental shelf by means of objectively fitted stream function fields the 32 month mean velocity stream function patterns generally support the cochrane and kelly 1986 circulation schema for the shelf circulation in which an elongated cyclonic gyre exists during the nonsummer period september through may but with flow in the summer june to august directed upcoast toward the mississippi delta over the entire shelf there exists significant interannual variability of the stream function fields especially in the transition period from spring to summer to fall and along the shelf break strong upcoast downcoast currents dominate at the western shelf break associated with the presence of energetic anticyclones cyclones the dominant pattern of stream function variability deduced by empirical orthogonal function eof analysis of 32 individual monthly mean patterns contains about 89 of the variance and shows a simple shelf wide along shelf pattern of circulation the monthly evolution in amplitude of this dominant eof pattern clearly mimics the monthly evolution of the along shelf component of the wind with squared correlation of 0 83 this provides strong evidence that the seasonal variation of the shelf circulation is wind forced in support of cochrane and kelly the second and residual eofs show more complex features near the shelf break that are associated with loop current eddies known to impact the continental slope and shelf break

pseudotachylyte controversy fact or friction high speed slip experiments performed on westerly granite using friction welding apparatus reveal that comminution is an essential precursor to melting by friction observations of slip surfaces via analytical scanning electron microscopy sem document the following sequence of events occurring in 2 s with increasing velocity up to 2 m s fracture progressive comminution surface melting of mineral fragments fragment to fragment adhesion and finally production of a fragment laden melt supported suspension explosive dehydration and melting of the epidote group mineral allanite indicates that temperatures of at least 1000 c were realized at the interface this is corroborated by calculation of the temperature rise for the known operating conditions contrary to earlier proposals these results show that comminution and frictional melting are complementary and not mutually exclusive processes depending on the velocity shear stress displacement relations prevailing during frictional slip rocks produced in seismogenic zones can be predominantly comminuted wall rock or fragment melt mixes pseudotachylytes

fluvial erosion transport equation of landscape evolution models revisited we present a mesoscale erosion deposition model which differs from previous landscape evolution models equations by taking explicitly into account a mass balance equation for the streamflow the geological and hydrological complexity is lumped into two basic fluxes erosion and deposition and two averaged parameters unit width discharge q and stream slope s the model couples the dynamics of streamflow and topography through a sediment transport length function x q which is the average travel distance of a particle in the flow before being trapped on topography this property reflects a time lag between erosion and deposition which allows the streamflow not to be instantaneously at capacity the so called x q model may reduce either to transport limited or to detachment limited erosion modes depending on x but it also may not we show in particular how it does or does not for steady state topographies long term evolution and high frequency base level perturbations apart from the unit width discharge and the settling velocity the x q function depends on a dimensionless number encompassing the way sediment is transported within the streamflow using models of concentration profile through the water column we show the dependency of this dimensionless coefficient on the rouse number we discuss how consistent the x q model framework is with bed load scaling expressions and einstein s conception of sediment motion

earth s surface responses during geodynamic evolution numerical insight from the southern east china sea continental shelf basin west pacific abstract the interaction between the earth s surface and deep geodynamic processes has a great influence on sedimentary patterns and characteristics of sedimentary systems especially in the continental margin such as the southern part of the east china sea continental shelf basin ecscsb however the exact processes and dynamics are poorly understood the numerical tool badlands was adopted to simulate the geological evolution of the southern ecscsb during the mesozoic transitional regime of the west pacific continental margin between 200 and 100 ma the numerical model involving four dimensional 4d sequence stratigraphy was validated by comparing with the tectono morphology sedimentary environments and sediment distribution according to our findings the transition was mainly controlled by three structural stages the first transitional stage of the southern ecscsb was mainly controlled by lithospheric scale tectonic evolution in the second stage the dynamic topography contributed to slow regional uplift while the last stage showed mantle induced dynamic subsidence the model results on 4d geomorphic characteristics sediment distribution of basin evolution and deep dynamic topography provided a quantitative image for geological evolution of the west pacific continental margin in the mesozoic

a mechanism to explain the generation of earthquake lights explanations of how earthquake lights might arise have failed to show how large charge densities can be concentrated and sustained in a conductive earth a physical model is proposed based on frictional heating of the fault that solves this and related problems

a sediment transport model for incision of gullies on steep topography 1 we have conducted surveys of gullies that developed in a small steep watershed in the idaho batholith after a severe wildfire followed by intense precipitation we measured gully length and cross sections to estimate the volumes of sediment loss due to gully formation these volume estimates are assumed to provide an estimate of sediment transport capacity at each survey cross section from the single gully forming thunderstorm sediment transport models commonly relate transport capacity to overland flow shear stress which is related to runoff rate slope and drainage area we have estimated the runoff rate and duration associated with the gully forming event and used the sediment volume measurements to calibrate a general physically based sediment transport equation in this steep high shear stress environment we find that a shear stress exponent of 3 corresponding to drainage area and slope exponents of m 2 1 and n 2 25 match our data this shear stress exponent of 3 is approximately 2 times higher than those for bed load transport in alluvial rivers but is in the range of shear stress exponents derived from flume experiments on steep slopes and with total load equations the concavity index of the gully profiles obtained theoretically from the area and slope exponents of the sediment transport equation c m 1 n agrees well with the observed profile concavity of the gullies our results although preliminary because of the uncertainty associated with the sediment volume estimates suggest that for steep hillslopes such as those in our study area a greater nonlinearity in the sediment transport function exists than that assumed in some existing hillslope erosion models which calculate sediment transport capacity using the bed load equations developed for rivers

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

subtidal circulation on the alabama shelf during the deepwater horizon oil spill 1 water column velocity and hydrographic measurements on the inner alabama shelf are used to examine the flow field and its forcing dynamics during the deepwater horizon oil spill disaster in the spring and summer of 2010 comparison between two sites provides insight into the flow variability and dynamics of a shallow highly stratified shelf in the presence of complicating geographic and bathymetric features seasonal currents reveal a convergent flow with strong highly sheared offshore flow near a submarine bank just outside of mobile bay at synoptic time scales the flow is relatively consistent with typical characteristics of wind driven ekman coastal circulation analysis of the depth averaged along shelf momentum balance indicates that both bottom stress and along shelf pressure gradient act to counter wind stress as a consequence of the along shelf pressure gradient and thermal wind shear flow reversals in the bottom currents can occur during periods of transitional winds despite the relatively short distance between the two sites 14 km significant spatial variability is observed this spatial variability is argued to be a result of local variations in the bathymetry and density field as the study region encompasses a submarine bank near the mouth of a major freshwater source given the physical parameters of the system along shelf flow in this region would be expected to separate from the local isobaths generating a mean offshore flow the local highly variable density field is expected to be in part responsible for the differences in the vertical variability in the current profiles

pressure related feedback processes in the generation of pseudotachylytes pseudotachylyte formation is typically viewed as a self limiting process quantitative models have demonstrated that frictional melting is possible at seismic slip rates but once a thin film of melt forms on a seismic fault plane the dramatic decrease in fault friction is thought to suppress further melting volumes of melt generated pseudotachylyte observed in field studies however are in many cases substantially larger than the amounts of frictional melt predicted by theoretical models this suggests that previously unrecognized physical processes may enhance melting during seismic slip localized decompression at dilational jogs may be one such phenomenon transient unloading could play two important roles in the dynamics of pseudotachylyte generation first by setting up significant fluid pressure gradients it would lead to rapid migration of the melt to sites of low pressure thereby reestablishing frictional contact across the fault surface and favoring further melt generation second at significant depths sudden depressurization might lead to in situ decompression melting

topographic evolution and morphology of surfaces evolving in response to coupled fluvial and hillslope sediment transport 1 this paper quantifies how the ratio of sediment transport on hillslopes to sediment transport in channels influences surface and channel network morphologies and the dynamics of topographic evolution this problem is investigated by development and investigation of a simple deterministic model incorporating mass balance of sediment and runoff coupled with a law combining dispersive and concentrative sediment transport processes our analysis includes the identification of a new nondimensional parameter de that is a function of rainfall system size rock type and hydraulic regime and that is a measure of the relative importance of fluvial and hillslope sediment transport we show that de has an important influence on the surface morphology e g total exposed surface area and interface width which reflects surface roughness and relief channel network form e g channel sinuosity channel spacing and timescale of surface evolution surface and channel network morphologies are also strongly influenced by the overall surface slope relative to the magnitude of initial topographic roughness topographic evolution occurs in distinct phases of relief growth and decay the transition between which is controlled by a saturation phenomenon related to the growth of spatial correlations the scaling behavior of simulated topography with respect to both time and space is obtained and is shown to be independent of de roughness exponents are found to be independent of de but dependent on the magnitude of initial roughness interface width is shown to grow and decay as a logarithm of time

the volcano electric effect 1 the formation of a magmatic intrusion at depth is responsible for the formation of various thermohydromechanical thm disturbances including the upsurge of shock waves and diffusion of pressure fronts in the volcanic system we couple electromagnetic theory maxwell equations and thermoporoelasticity biot equations to look at the ground surface electrical signature of these thm disturbances the nature of this coupling is electrokinetic i e associated with water flow relative to the mineral framework and the drag of the excess of charge located in the vicinity of the pore water mineral interface the groundwater flow disturbance being related here to the thm disturbances in drained conditions a new set of laboratory data shows that the electrokinetic coupling is very substantial in fractured basaltic and volcaniclastic materials and in scoria with several hundreds of millivolts of electrical potential gradient produced per megapascal of pore fluid pressure variations our theoretical analysis predicts the diffusion of electromagnetic disturbances and quasi static electrical signals these signals can be used as precursors of a volcanic eruption indeed electromagnetic phenomena recorded at the ground surface of a volcanic system once properly filtered to remove external contributions provide a direct and quasi instantaneous insight into the thm disturbances occurring in the heart of the volcanic structure prior and during a volcanic event tomography of the quasi static electrical field is discussed and applied to self potential profiles performed at the piton de la fournaise volcano during the preparation phase of the march 1998 eruption

the origin of high magnetic remanence in fault pseudotachylites theoretical considerations and implication for coseismic electrical currents abstract several examples of fault related pseudotachylites display a significantly higher initial magnetic susceptibility than their granitic host rock 10 1 to 20 1 these higher values are attributed to the presence of fine magnetic particles formed during melt quenching the hysteresis properties of the particles indicate a single domain sd to pseudo single domain psd magnetic grain size the curie temperature tc of the magnetic particles is close to 580 c the natural remanent magnetization nrm of these pseudotachylites is also significantly higher than that of the host rock up to 300 1 such anomalously high remanence cannot be explained by a magnetization acquired in the earth s magnetic field regardless of pseudotachylite age ground lightning and other strong electric pulses can cause anomalously high nrm intensities a ground lightning explanation seems unlikely to explain the systematically high nrm intensities particularly in the case of recently exposed samples that have been collected from active quarries alternatively high nrm intensities could be explained by earthquake lightning eql a seismic phenomenon occasionally reported in connection with large magnitude earthquakes m 6 0 the coseismic electrical properties of the pseudotachylite vein host rock system are characterized by 1 a core of molten material high conductivity 2 vapor rich margins of thermally and mechanically fractured host rocks low conductivity and 3 moderately fractured to undeformed host rock normal conductivity such a core conductor bordered by insulating margins is potentially responsible for the propagation of eql pulses the coseismic thermal history of pseudotachylite veins has been modeled in 2 d using conductive heat transfer equations it shows that eql can be recorded only during a brief time interval less than 1 min for a given vein thickness and host rock temperatures if the vein is too thick or if the host rock is too hot the pseudotachylite remains above tc after the electric pulse has lapsed

soil erosion by surface water flow on a stony semiarid hillslope soil erosion on hillslopes occurs by processes of soil splash from raindrop impacts and sediment entrainment by surface water flows this study investigates the process of soil erosion by surface water flow on a stony soil in a semiarid environment a field experimental method was developed whereby erosion by concentrated flow could be measured in predefined flow areas without disturbing the soil surface the method allowed for measurements in this study of flow erosion at a much wider range of slopes 2 6 to 30 1 per cent and unit discharge rates 0 0007 to 0 007 m2 s 1 than have been previously feasible flow velocities were correlated to discharge and hydraulic radius but not to slope the lack of correlation between velocity and slope might have been due to the greater rock cover on the steeper slopes which caused the surface to be hydraulically rougher and thus counteract the expected effect of slope on flow velocity the detachment data illustrated limitations in applying a linear hydraulic shear stress model over the entire range of the data collected flow detachment rates were better correlated to a power function of either shear stress r2 0 51 or stream power r2 0 59 published in 1999 by john wiley sons ltd

the relationship between drainage density erosion rate and hilltop curvature implications for sediment transport processes drainage density is a fundamental landscape metric describing the extent of the fluvial network we compare the relationship between drainage density dd and erosion rate e using the channel hillslope integrated landscape development child numerical model we find that varying the channel slope exponent n in detachment limited fluvial incision models controls the relationship between dd and e with n 1 resulting in increasing dd with e if all other parameters are held constant this result is consistent when modeling both linear and nonlinear hillslope sediment flux we also test the relationship between dd and e in five soil mantled landscapes throughout the usa feather river ca san gabriel mountains ca boulder creek co guadalupe mountains nm and bitterroot national forest id for two of these field sites we compare dd to cosmogenic radionuclide crn derived erosion rates and for each site we use mean hilltop curvature as a proxy for erosion rate where crn derived erosion rates are not available we find that there is a significant positive relationship between dd e and hilltop curvature across every site with the exception of the san gabriel mountains ca this relationship is consistent with an n exponent greater than 1 suggesting that at higher erosion rates the transition between advective and diffusive processes occurs at smaller contributing areas in soil mantled landscapes

high magnetic susceptibility produced by thermal decomposition of core samples from the chelungpu fault in taiwan abstract we carried out thermomagnetic susceptibility analyses of fault rocks from core samples from hole b of the taiwan chelungpu fault drilling project tcdp to investigate the cause of high magnetic susceptibilities in the fault core test samples were thermally and mechanically treated by heating to different maximum temperatures of up to 900 c and by high velocity frictional tests before magnetic analyses thermomagnetic susceptibility analyses of natural fault rocks revealed that magnetization increased at maximum heating temperatures above 400 c in the heating cycle and showed three step increases at 600 to 550 c and at 300 c during the cooling cycle these behaviors are consistent with the presence of pyrite siderite and chlorite suggesting that tcdp gouge originally included these minerals which contributed to the generation the magnetic susceptibility by thermomechanical reactions the change in magnetic susceptibility due to heating of siderite was 20 times that obtained by heating pyrite and chlorite so that only a small fraction of siderite decomposition is enough to cause the slight increase of the susceptibility observed in the fault core color measurement results indicate that thermal decomposition by frictional heating took place under low oxygen conditions at depth which prevented the minerals from oxidizing to reddish hematite this finding supports the inference that a mechanically driven chemical reaction partly accounts for the high magnetic susceptibility a kinetic model analysis confirmed that frictional heating can cause thermal decomposition of siderite and pyrite our results show that decomposition of pyrite to pyrrhotite siderite and to some extent chlorite to magnetite is the probable mechanism explaining the magnetic anomaly within the chelungpu fault zone

modelling centennial sediment waves in an eroding landscape catchment complexity sediment flux dynamics in fluvial systems have often been related to changes in external drivers of topography climate or land cover it is well known that these dynamics are non linear recently model simulations of fluvial activity and landscape evolution have suggested that self organization in landscapes can also cause internal complexity in the sedimentary record in this contribution one particular case of self organization is explored in the sabinal field study area spain where several dynamic zones of sedimentation and incision are observed along the current river bed whether these zones can be caused by internal complexity was tested with landscape evolution model lem lapsus landscape process modelling at multi dimensions and scales during various 500 year simulations zones of sedimentation appear to move upstream and downstream in eroding river channels waves these waves are visualized and characterized for a range of model settings under constant external forcing and the self organizing process behind their occurrence is analysed results indicate that this process is not necessarily related to simplifications in the model and is more generic than the process of bed armouring that has recently been recognized as a cause for complexity in lem simulations we conclude that autogenic sediment waves are the result of the spatial propagation in time of feedbacks in local transport limited deposition and detachment limited erosion conditions

electro magnetic earthquake bursts and critical rupture of peroxy bond networks in rocks abstract we propose a mechanism for the low frequency electromagnetic emissions and other electromagnetic and electric phenomena which have been associated with earthquakes the mechanism combines the critical earthquake concept and the concept of crust acting as a charging electric battery under increasing stress the electric charges are released by activation of dormant charge carriers in the oxygen anion sublattice called peroxy bonds or positive hole pairs php where a php represents an o 3 x oo yo 3 with x y si 4 al 3 i e o in a matrix of o 2 of silicates we propose that php are activated by plastic deformations during the slow cooperative build up of stress and the increasingly correlated damage culminating in a large critical earthquake recent laboratory experiments indeed show that stressed rocks form electric batteries which can release their charge when a conducting path closes the equivalent electric circuit we conjecture that the intermittent and erratic occurrences of em signals are a consequence of the progressive build up of the battery charges in the earth crust and of their release when crack networks percolate through the stressed rock volumes providing a conductive pathway for the battery currents to discharge em signals are thus expected close to the rupture either slightly before or after that is when percolation is most favored the proposed mechanism should be relevant for the broader understanding of fractoemissions

a simple universal equation for grain settling velocity abstract a new equation is presented for sediment fall velocity as a function of grain diameter for given values of fluid viscosity and fluid and solid density sediment fall velocity is a fundamental parameter in the modeling and interpretation of fluviatile and coastal deposition the equation applies to the entire range of viscous to turbulent conditions and its simple explicit form makes it easy to use in computer models and other applications in sedimentology geomorphology and engineering the equation is derived from dimensional analysis and converges on stokes law for small grains and a constant drag coefficient for large grains its two physically interpretable parameters are easily adjusted for shape effects or for the use of sieve diameter rather than nominal grain diameter it gives a close fit to published and new experimental data for both quartz sand and low density materials with no more error than previous equations of more complicated form

pseudotachylytes generated during seismic faulting and eclogitization of the deep crust pseudotachylytes are typically interpreted to have formed by frictional melting during coseismic faulting within the upper to middle crust pseudotachylytes in the bergen arcs of western norway contain microlites including omphacite garnet plagioclase and quartz this eclogite facies assemblage is stable at temperatures of about 800 c and pressures of 18 to 19 kilobars corresponding to depths of 60 kilometers or more the pseudotachylytes are exposed in grenvillian granulites that locally underwent fluid induced eclogitization and corresponding volume reduction of approximately 10 percent during the caledonian continental collision the pseudotachylytes may have formed as a result of the rapid relaxation of stresses caused by the eclogitization process

scaling regimes of local slope versus contributing area in digital elevation models four scaling regimes are observed in digital elevation models dems when the average local slope is calculated for pixels grouped according to the values of the contributing area threshold criteria proposed by various researchers to identify the extent of the channel network are examined relative to the slope area scaling diagram the scaling response observed in dems is reproduced with a landscape evolution and channel network growth model originally developed by willgoose et al 1989 the threshold criterion proposed in this model is a useful tool to separate two different slope area scaling regimes observed in dem data

comment on a paper the origin of high magnetic remanence in fault pseudotachylites theoretical considerations and implication for coseismic electrical currents by e c ferre m s zechmeister j w geissman n mathana sekaran and k kocak

electrical conductivity of dry lower crustal rocks this study provides values of electrical conductivity of possible lower crustal materials to assist interpretation of lower crustal magnetotelluric soundings we present mean values of conductivity measurements collected from the literature for dry mafic and silicic rocks in the temperature range of 500 c to 1000 c we observe statistically significant differences between rock types mafic rocks are better conductors than granites by about half an order of magnitude and within the mafic group aphanitic fine grained rocks have higher conductivity than phaneritic coarse grained ones best fitting curves of log conductivity versus temperature are presented for each rock type to show mean log conductivity values together with standard deviations so that most probable temperature ranges can be inferred from conductivity because the laboratory rocks are dry their conductivities are lower at a given temperature than they would be if fluids or volatiles were present hence any temperatures inferred from

electromagnetic precursors to earthquakes in the ulf band a review of observations and mechanisms despite over 2 decades of international and national monitoring of electrical signals with the hope of detecting precursors to earthquakes the scientific community is no closer to understanding why precursors are observed only in some cases laboratory measurements have demonstrated conclusively that self potentials develop owing to fluid flow and that both resistivity and magnetization change when rocks are stressed however field experiments have had much less success many purported observations of low frequency electrical precursors are much larger than expectations based on laboratory results in some cases no precursors occurred prior to earthquakes or precursory signals were reported with no corresponding coseismic signals nonetheless the field experiments are in approximate agreement with laboratory measurements maximum resistivity changes of a few percent have been observed prior to some earthquakes in china but the mechanism causing those changes is still unknown anomalous electric and magnetic fields associated with fluid flow prior to earthquakes may have been observed finally piezomagnetic signals associated with stress release in earthquakes have been documented in measurements of magnetic fields

low frequency circulation on the texas louisiana continental shelf for the texas louisiana coast west of 92 5 w long series of data from near freeport texas together with shorter series from other locations show strong response of coastal current to wind stress in agreement with coastal jet concepts we infer from coastal winds scattered current measurements and distributions of sea surface salinity and geopotential that a cyclonic gyre elongated along the shelf is the dominant feature of the prevailing shelf circulation the inshore limb of the gyre is the coastal jet driven by wind with a west or southward downcoast component which prevails along much of the coast except in july august because the coast is concave the shoreward prevailing wind results in a convergence of coastal currents which marks the downcoast extent of the gyre corresponding to the convergence is a seaward flow which forms the southwest limb of the gyre a prevailing countercurrent north or eastward flow along the shelf break includes the outer limb of the gyre the eastern shoreward flowing limb of the gyre corresponds to divergence along the coast centered near 92 5 w the convergence at the western or southern end of the gyre migrates seasonally with the direction of the prevailing wind reaching south of the rio grande mouth in fall and the cameron offing in july the gyre is normally absent in july but reappears in august september when a downcoast wind component develops

electric currents along earthquake faults and the magnetization of pseudotachylite veins pseudotachylites occur in the form of thin glassy veins quenched from frictional melts along the fault planes of major earthquakes they contain finely grained magnetite and often exhibit a high natural remanent magnetization nrm high nrm values imply strong local electric currents these currents must persist for some time while the pseudotachylite veins cool through the curie temperature of magnetite around 580 c there is no generally accepted theory explaining how such powerful persistent currents may be generated along the fault plane data presented here suggest the activation of electronic charge carriers which are present in igneous rocks in a dormant inactive form these charge carriers can be awakened by the application of stress they are electrons and defect electrons also known as positive holes or p holes for short while p holes are capable of spreading out of the stressed rock volume into adjacent p type conductive unstressed rocks electrons require a connection to the hot n type conductive lower crust however as long as the downward electron flow is not connected the circuit is not closed hence with the outflow of p holes impeded no current can be sustained this situation is comparable to that of a charged battery where one pole remains unconnected the friction melt that forms coseismically during rupture provides a conductive path downward which closes the circuit this allows a current to flow along the fault plane extrapolating from laboratory data every km 3 of stressed igneous rocks adjacent to the fault plane can deliver 10 3 10 5 a hence the current along the fault plane will not be limited by the number of charge carriers but more likely by the electronic conductivity of the cooling pseudotachylite vein the sheet current will produce a magnetic field whose vectors will lie in the fault plane and perpendicular to the flow direction 2006 elsevier b v all rights reserved

longitudinal profile development into bedrock an analysis of hawaiian channels analysis of topographic maps of rivers incised into dated hawaiian lava flows shows that the long term average bedrock erosion rate along certain reaches is linearly related to stream power field observations suggest that two processes may control hawaiian channel downcutting 1 stream power dependent erosion including abrasion of the channel bed by transported particles and 2 step wise lowering caused by knickpoint propagation modeling results indicate that a simple stream power dependent erosion law predicts the straight to weakly convex longitudinal profiles characteristic of kauai channels but is insufficient to predict two other characteristic features the upslope propagation of knickpoints and the straight 5 8 channel slopes below the knickpoints thus more than this single transport law is apparently required to model bedrock channel incision field surveys also indicate that significant portions of the channel lengths below the knickpoints are mantled with large boulders we propose that

piezoelectric effects in quartz rich rocks abstract piezoelectricity a polarization of charge produced by an applied stress occurs in many minerals it is particularly strong in quartz aggregates of piezoelectric grains are themselves piezoelectric if the grains are suitably aligned such aggregates may be said to have a piezoelectric fabric thus quartz rich rocks may possess a piezoelectric fabric and this paper discusses the various possible fabrics to test whether a piezoelectric fabric might be detected in a quartz rich rock apparatus was built that hydraulically applied a sinusoidal stress to cubic specimens the three resulting orthogonal polarizations of charge were measured via a charge amplifier a specimen of pure quartz was used to verify the experimental method and to ensure that absolute piezoelectric moduli were being measured rocks with and without preferred orientation were tested of the latter types those containing little or no free quartz marble basalt did not exhibit measurable piezoelectric effects however all quartz rich rocks quartzites granites gneisses mylonites did show piezoelectric effects when stressed these effects were in two categories 1 1 effects due to piezoelectric fabrics called true piezoelectric effects 2 2 effects due to random distributions of the piezoelectric vectors called statistical effects to distinguish between these two effects three criteria were used firstly the measured effects were compared with the expected statistical effect for a rock of that grain size and composition secondly where possible multiple specimens were cut from the one rock sample all specimens with the same orientation specimens from a rock with a piezoelectric fabric should show similar results thirdly the optically observed c axis distribution and orientation was compared with the piezoelectrically predicted fabric and orientation this paper shows that while most rocks gave results consistent with statistical effects from a non polar or random distribution some rocks exhibited a true piezoelectric effect due to fabric this effect may be used with some imprecision to locate the a axes and c axes of quartz in the aggregate the polarities of the a axes are also obtained

channelization cascade in landscape evolution the hierarchy of channel networks in landscapes displays features that are characteristic of nonequilibrium complex systems here we show that a sequence of increasingly complex ridge and valley networks is produced by a system of partial differential equations coupling landscape evolution dynamics with a specific catchment area equation by means of a linear stability analysis we identify the critical conditions triggering channel formation and the emergence of characteristic valley spacing the ensuing channelization cascade described by a dimensionless number accounting for diffusive soil creep runoff erosion and tectonic uplift is reminiscent of the subsequent instabilities in fluid turbulence while the structure of the simulated patterns is indicative of a tendency to evolve toward optimal configurations with anomalies similar to dislocation defects observed in pattern forming systems the choice of specific geomorphic transport laws and boundary conditions strongly influences the channelization cascade underlying the nonlocal and nonlinear character of its dynamics

the importance of spatially heterogeneous erosivity and the cumulative area distribution within a basin evolution model abstract topography reflects the terrain composition and the forces to which it is exposed the elements that control this shape are intuitive precipitation wind soil composition geologic activity lithology and vegetation each of these elements varies naturally in space a model of basin evolution is shown to produce quantitatively different topography for different relative magnitudes of diffusive and incisive erosion processes spatial heterogeneities in erosivity also influence the simulated topography the calibration of this evolution model is compared to observed topography the calibration process ultimately hinges on quantification of the aggregation pattern of the basin through analysis of the cumulative area distribution the effect of spatially heterogeneous erosivity is shown to be crucially important to reproduce the cumulative area distribution of observed topography

controls on the spacing of first order valleys 1 many landscapes are composed of ridges and valleys that are uniformly spaced even where valley locations are not controlled by bedrock structure models of long term landscape evolution have reproduced this phenomenon yet the process by which uniformly spaced valleys develop is not well understood and there is no quantitative framework for predicting valley spacing here we use a numerical landscape evolution model to investigate the development of uniform valley spacing we find that evenly spaced valleys arise from a competition between adjacent drainage basins for drainage area a proxy for water flux and that the spacing becomes more uniform as the landscape approaches a topographic equilibrium valley spacing is most sensitive to the relative rates of advective erosion processes such as stream incision and diffusion like mass transport such as soil creep and less sensitive to the magnitude of a threshold that limits the spatial extent of stream incision analysis of a large number of numerical solutions reveals that valley spacing scales with a ratio of characteristic diffusion and advection timescales that is analogous to a peclet number we use this result to derive expressions for equilibrium valley spacing and drainage basin relief as a function of the rates of advective and diffusive processes and the spatial extent of the landscape the observed scaling relationships also provide insight into the cause of transitions from rill like drainage networks to branching networks the spatial scale of first order drainage basins the contributing area at which hillslopes transition into valleys and the narrow range of width to length ratios of first order basins

fluvial and slope wash erosion of soil mantled landscapes detachment or transport limited many numerical landform evolution models assume that soil erosion by flowing water is either purely detachment limited i e erosion rate is related to the shear stress power or velocity of the flow or purely transport limited i e erosion deposition rate is related to the divergence of shear stress power or velocity this paper reviews available data on the relative importance of detachment limited versus transport limited erosion by flowing water on soil mantled hillslopes and low order valleys field measurements indicate that fluvial and slope wash modification of soil mantled landscapes is best represented by a combination of transport limited and detachment limited conditions with the relative importance of each approximately equal to the ratio of sand and rock fragments to silt and clay in the eroding soil available data also indicate that detachment entrainment thresholds are highly variable in space and time in many landscapes with local threshold values dependent on vegetation cover rock fragment armoring surface roughness soil texture and cohesion this heterogeneity is significant for determining the form of the fluvial slope wash erosion or transport law because spatial and or temporal variations in detachment entrainment thresholds can effectively increase the nonlinearity of the relationship between sediment transport and stream power results from landform evolution modeling also suggest that aside from the presence of distributary channel networks and autogenic cut and fill cycles in non steady state transport limited landscapes it is difficult to infer the relative importance of transport limited versus detachment limited conditions using topography alone copyright 2011 john wiley sons ltd

experimental study on characteristics of surface potential and current induced by stress on coal mine sandstone roof abstract rocks generate voltage and current when subjected to load hence the study of their characteristics is critical to the prevention and management of mine dynamic disasters and their secondary impacts to investigate the characteristics of surface potential and current induced by stress on coal mine sandstone roof an experimental scheme for determining the mechanical electrical characteristics of rocks is constructed the aforementioned system tests the evolution rules of current and voltage generated by the coal mine sandstone roof at different loading rates the formation mechanism and coupling rules with mechanical properties of sandstone are also analysed experimental results show that although loading rates may differ the variations of pressure stimulated current psc and pressure stimulated voltage psv curves are similar throughout the loading process the psc is divided into three stages rapid growth slow growth and peak on the other hand the psv curve exhibits a double peak characteristic the loading rate changes the current and voltage growth rates and peak values when combined with mechanical properties it can be observed that the psc is related to the effective elastic modulus whereas the psv is related to micro crack and macro crack events in rocks the current and voltage generated by the coal mine sandstone roof subjected to load are consistent with stress the mechanical electrical properties of sandstone indicate that the change processes in the psc and psv result from the coupling effects of various mechanisms in the compaction stage these are mainly caused by the piezoelectric effect of sandstone in the elastic plastic deformation stage they are primarily generated by the electric dipoles formed by micro cracks in the sandstone fracture deformation stage the change processes are mainly caused by the crack tip discharge this study provide an experimental basis and practical results that reflect the microscale process and electrical precursors of sandstone fracturing

a numerical study of sea breeze driven ocean poincare wave propagation and mixing near the critical latitude abstract near the vicinity of 30 latitude the coincidence of the period of sea breeze and the inertial period of the ocean leads to a maximum near inertial ocean response to sea breeze this produces a propagating inertial internal poincare wave response that transfers energy laterally away from the coast and provides significant vertical mixing in this paper the latitudinal dependence of this wave propagation and its associated vertical mixing are investigated primarily using a nonlinear numerical ocean model three dimensional idealized simulations show that the coastal oceanic response to sea breeze is trapped poleward of 30 latitude however it can propagate offshore as poincare waves equatorward of 30 latitude near 30 latitude the maximum oceanic response to sea breeze moves offshore slowly because of the near zero group speed of poincare waves at this latitude the lateral energy flux convergence plus the energy input from the wind is maximum near the critical latitude leading to increa

landscape evolution models a review of their fundamental equations abstract this paper reviews the main physical laws proposed in landscape evolution models lems it discusses first the main partial differential equations involved in these models and their variants these equations govern water runoff stream incision regolith bedrock interaction hillslope evolution and sedimentation a synthesis of existing lems is proposed it proposes three models with growing complexity and with a growing number of components two equation models with only two components governing water and bedrock evolution three equation models with three components where water bedrock and sediment interact and finally models with four equations and four interacting components namely water bedrock suspended sediment and regolith this analysis is not a mere compilation of existing lems it attempts at giving the simplest and most general physically consistent set of equations coping with all requirements stated in lems and lem software three issues are in particular addressed and hopefully resolved the first one is a correct formulation of the water transport equation down slopes a general formulation for this equation is proposed coping not only with the simplest form computing the drainage area but also with a sound energy dissipation argument associated with the saint venant shallow water equations the second issue arises from the coexistence of two competing modes namely the detachment limited erosion mode on hillslopes and the transport limited sediment transport on river beds the third issue linked to the second is the fact that no conservation law is available for material in these two modes a simple solution proposed to resolve these issues is the introduction as suggested by several authors of an additional variable for suspended sediment load in water with only three variables and three equations the above mentioned contradictions seem to be eliminated several numerical experiments on real digital elevation models dems illustrate the discussion and show results of landscape evolution with the proposed synthetic models

variation in the position of the upwelling front on the oregon shelf 1 as part of an experiment to study wind driven coastal circulation 17 hydrographic surveys of the middle to inner shelf region off the coast of newport or 44 65 n from roughly the 90 m isobath to the 10 m isobath were performed during summer 1999 with a small towed undulating vehicle the cross shelf survey data were combined with data from several other surveys at the same latitude to study the relationship between upwelling intensity and wind stress field a measure of upwelling intensity based on the position of the permanent pycnocline is developed this measure is designed so as to be insensitive to density modifying surface processes such as heating cooling buoyancy plumes and wind mixing it is highly correlated with an upwelling index formed by taking an exponentially weighted running mean of the alongshore wind stress this analysis suggests that the front relaxes to a dynamic geostrophic equilibrium on a timescale of roughly 8 days consistent with a similar analysis of moored hydrographic observations this relationship allows the amount of time the pycnocline is outcropped to be estimated and could be used with historical wind records to better quantify interannual cycles in upwelling

three dimensional landscape process modelling the effect of dem resolution many landscape models have been developed over the past decades however relatively little is known about handling the effects of changing spatial and temporal resolutions therefore resolution effects remain a factor of uncertainty in many hydrological and geomorphological modelling approaches in this paper we present an experimental multi scale study of landscape process modelling emphasis was laid on quantifying the effect of changing the spatial resolution upon modelling the processes of erosion and sedimentation a simple single process model was constructed and equal boundary conditions were created using artificial digital elevation models dems eliminated effects of landscape representation the only variable factors were dem resolution and the method of flow routing both steepest descent and multiple flow directions our experiments revealed an important dependency of modelled erosion and sedimentation rates on these main variables the general trend is an increase of erosion predictions with coarser resolutions an artificial mathematical overestimation of erosion and a realistic natural modelling effect of underestimating resedimentation cause this increasing the spatial extent eliminates the artificial effect while at the same time the realistic effect is enhanced both effects can be quantified and are expected to increase within natural landscapes the modelling of landscape processes will benefit from integrating these types of results at different resolutions

influence of mantle flow on the drainage of eastern australia since the jurassic period recent studies of the past eastern australian landscape from present day longitudinal river profiles and from mantle flow models suggest that the interaction of plate motion with mantle convection accounts for the two phases of large scale uplift of the region since 120 ma we coupled the dynamic topography predicted from one of these mantle flow models to a surface process model to study the evolution of the eastern australian landscape since the jurassic period we varied the rainfall regime erodibility sea level variations dynamic topography magnitude and elastic thickness across a series of experiments the approach accounts for erosion and sedimentation and simulates catchment dynamics despite the relative simplicity of our model the results provide insights on the fundamental links between dynamic topography and continental scale drainage evolution based on temporal and spatial changes in longitudinal river profiles as well as erosion and deposition maps we show that the motion of the australian plate over the convecting mantle has resulted in significant reorganization of the eastern australian drainage the model predicts that the murray river drained eastward between 150 and 120 ma and switched to westward draining due to the tilting of the australian plate from 120 ma first order comparisons of eight modeled river profiles and of the catchment shape of modeled murray darling basin are in agreement with present day observations the predicted denudation of the eastern highlands is compatible with thermochronology data and sedimentation rates along the southern australian margin are consistent with cumulative sediment thickness

streaming potential properties of westerly granite with applications this paper reports on laboratory measurements of the streaming potential properties of common minerals and in particular of westerly granite data are presented for these solids in contact with simple electrolytic solutions and in one case for temperature variation in the range 5 70 c for 1 1 electrolytes the ratio of the streaming potential coupling coefficient to fluid resistivity was approximately 4 mv atm m and for 2 1 electrolytes 2 mv atm m the effect of temperature was small 0 05 mv c temperature increase and indicates that the zeta potential was independent of temperature preliminary experimental results using mixed electrolytic solutions nacl cacl2 and two phase fluid flow are also described two phase flow can enhance streaming potentials by as much as a factor of 3 or 4 the laboratory data are used to interpret streaming potentials in geological problems such as earthquake prediction geothermal prospecting using the self potential method and surface conductivity contribution to the electrical resistivity of rocks

palaeomagnetism of the vredefort meteorite crater and implications for craters on mars magnetic surveys of the martian surface have revealed significantly lower magnetic field intensities over the gigantic impact craters hellas and argyre than over surrounding regions the reduced fields are commonly attributed to pressure demagnetization caused by shock waves generated during meteorite impact in the absence of a significant ambient magnetic field lower than average magnetic field intensities are also observed above the vredefort meteorite crater in south africa yet here we show that the rocks in this crater possess much higher magnetic intensities than equivalent lithologies found elsewhere on earth we find that palaeomagnetic directions of these strongly magnetized rocks are randomly oriented with vector directions changing over centimetre length scales moreover the magnetite grains contributing to the magnetic remanence crystallized during impact which directly relates the randomization and intensification to the impact event the strong and randomly oriented magnetization vectors effectively cancel out when summed over the whole crater seen from high altitudes as for martian craters the magnetic field appears much lower than that of neighbouring terranes implying that magnetic anomalies of meteorite craters cannot be used as evidence for the absence of the planet s internally generated magnetic field at the time of impact

seasonal circulation on the western shelf of the gulf of mexico using a high resolution numerical model 1 the seasonal circulation on the western shelf of the gulf of mexico is studied using a high resolution numerical simulation historical hydrographic data sea level data and satellite images three regions are distinguished the tamaulipas veracruz tave shelf the louisiana texas latex shelf and the western campeche bank on the tave shelf there is a swift reversal of the along shelf current downcoast from september to march and upcoast from may to august when there is upwelling due to offshore ekman transport circulation on the western campeche bank is upcoast throughout the year the latex shelf has a cyclonic circulation except during summer months when the flow is eastward during spring summer the upcoast current on the tave shelf reaches the southern texas shelf where it encounters a downcoast coastal current favoring offshore transports in the fall winter the downcoast current reaches the southern bay of campeche where it meets an opposing along shelf current generating seasonal offshore transports during fall and winter cool low salinity water from the mississippi and atchafalaya rivers is advected westward along the latex shelf onto the tave shelf developing along shelf fronts and temperature inversions commonly observed over the outer shelf and shelf break the main forcing over the western shelf of the gulf is the along coast wind stress component the existence of the cross shelf transports in the confluence regions is supported by chlorophyll a data up to 80 of the seasonal sea level variability is explained by the along shelf currents and the low frequency variability of the atmospheric sea level pressure

petrological architecture of a magmatic shear zone a multidisciplinary investigation of strain localisation during magma ascent at unzen volcano japan shearing of magma during ascent can promote strain localisation near the conduit margins anymechanical and thermal discontinuities associated with such events may alter the chemical physicaland rheological stability of the magma and thus its propensity to erupt lava spines can record suchprocesses preserving a range of macroscopic and microscopic deformation textures attributed toshearing and friction as magma ascends through the viscous brittle transition here we use a multi disciplinary approach combining petrology microstructures crystallography magnetics and experi mentation to assess the evidence role and extent of shearing across a marginal shear zone of the1994 1995 lava spine at unzen volcano japan our results show that crystals can effectively moni tor stress conditions during magma ascent with viscous remobilisation crystal plasticity and com minution all systematically increasing towards the spine margin accompanying this we find anincrease in mineral destabilisation in the form of pargasitic amphibole breakdown displaying tex tural variations across the shear zone from symplectitic to granular rims towards the spine margin in addition the compaction of pores chemical and textural alteration of interstitial glass and mag netic variations all change systematically with shear intensity the strong correlation between thedegree of shearing crystal deformation and disequilibrium features together with distinct magneticproperties implies a localised thermal input due to shear and frictional processes near the conduitmargin during magma ascent this was accompanied by late stage or post emplacement fluid andgas induced alteration of the gouge as well as oxidation and glass devitrification understandingand recognising evidence for strain localisation during magma ascent may therefore be vital whenassessing factors that regulate the style of volcanic eruptions which may provide insights into thecryptic shifts from effusive to explosive activity as observed at many active lava domes

analysis of ultralow frequency electromagnetic field measurements associated with the 1999 m 7 1 hector mine california earthquake sequence we installed two electromagnetic em monitoring systems in the im mediate aftermath of the 16 october 1999 hector mine earthquake to search for possible continuing ultralow frequency ulf em activity due to the mainshock as well as for any precursory or coseismic em signals that might be associated with large aftershocks we installed the first portable monitoring system 2 5 days after the m 7 1 hector mine earthquake at a location 16 km southeast of the epicenter and 2 km east of the surface rupture a second system was installed on 29 october 1999 10 km northwest of the epicenter and within 100 m of the surface rupture our continuous measurements of multiple component magnetic field electric field and ground motion span the low frequencies appropriate for recording possible em sig nals generated at seismogenic depths and were carried out during 3 months following the mainshock continuous magnetic field measurements at observatory em stations operating in california are used as remote reference sites to remove global atmo spheric signals which helps isolate local terrestrial sources of interest our analysis of preseismic ulf em variations the coseismic response the 2 month long magnetic field power spectra and electric field polarization shows no anomalous behavior clearly associated with seismic activity

high pressure metamorphism and deep crustal seismicity evidence from contemporaneous formation of pseudotachylytes and eclogite facies coronas the metamorphic complex of the western gneiss region wgr norway constitutes the root of the caledonian mountain belt and experienced temperatures of 700 800 c and pressures in excess of 20 kbar during peak metamorphism mafic bodies surrounded by strongly banded felsic gneisses commonly exhibit variable reequilibration to granulite and eclogite facies conditions and locally preserve igneous minerals and textures the krakeneset gabbro located on the island of vagsoy in the mixed hp uhp zone of the western wgr display evidence for extensive metastability through the entire prograde and retrograde p t histories eclogite constitutes less than a few percent of the total volume of the body and high pressure assemblages typically form thin coronas around magmatic phases or occur along localized zones of brittle deformation and fluid infiltration the gabbro displays pseudotachylyte vein networks that define subparallel brittle fault zones 50 cm wide transecting the gabbro body the pseudotachylytes contain m to mm scale amoeboid and dendrite like textures of garnet and plagioclase with inclusions of the eclogite facies minerals orthopyroxene omphacite amphibole and dolomite suggesting rapid disequilibrium growth of minerals during high pressure conditions textural and petrological evidence from pseudotachylytes and corona structures show that the growth of these unusual textures occurred shortly after pseudotachylyte crystallization by a process of rapid solid state alteration of a microcrystalline pseudotachylyte matrix the pseudotachylyte lined fault zones are in close spatial association with numerous amphibole carbonate filled hydrofractures with conspicuous fracture parallel alteration zones defined by hydrous eclogite facies assemblages these eclogite facies hydrofractures testify to the existence of high fluid pressures and to fluid infiltration following brittle failure during high grade metamorphic conditions geothermobarometric estimates ca t 650 700 c p 20 kbar and petrological data imply that hydrofracturing pseudotachylyte crystallization and the subsequent pseudotachylyte alteration process must have occurred during high pressure metamorphism our observations are suggestive of a deep crustal earthquake scenario where a high pressurized fluid phase plays a double role by causing both seismic failure through the embrittlement effect and facilitating eclogitization of the metastable anhydrous gabbro metamorphic reaction along hydrofractures and fault planes led to the development of eclogite facies foliation fabrics and illustrate the rheological change from brittle to plastic behavior associated with the gabbro to eclogite transition the formation of weak deep crustal shear zones following brittle failure represents an arrested initiation of the physical breakup and metamorphic reequilibration of the krakeneset gabbro during its residence deep in the former caledonian collision zone

numerical treatment of cross shelf open boundaries in a barotropic coastal ocean model abstract using a barotropic coastal ocean model with a straight coastline and uniform cross shelf bottom slope seven different cross shelf open boundary conditions four of which are applied in either implicit or explicit form are compared in three numerical experiments 1 a mound of water is allowed to collapse and radiate waves toward the open boundaries 2 a uniform alongshelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment 3 a uniform cross shelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment the boundary condition which is most transparent to waves consists of a sponge at the outer edge of the model domain with an orlanski radiation condition at the outer edge of the sponge several open boundary conditions perform adequately in the wind stress experiments but the orlanski radiation condition alone without a sponge appears to give the best total performance of thes

near resonant ocean response to sea breeze on a stratified continental shelf abstract the spatial structure and temporal characteristics of sea breeze and the associated coastal ocean response in the northwest gulf of mexico are investigated using moored instruments hydrographic stations and wind measurements near the study area of 30 n motions in the diurnal inertial band dib may be significantly enhanced by a near resonant condition between local inertial and diurnal forcing frequencies wavelet analysis is used to quantify the results results indicate that diurnal sea breeze variability peaks in summer and extends at least 300 km offshore with continuous seaward phase propagation the maximum dib oceanic response occurs in june when there is a shallow mixed layer strong stratification and an approximately 10 day period of continuous sea breeze forcing dib current variance decreases in july and august as the consequence of the deepening of the mixed layer and a more variable phase relationship between the wind and current river discharge varies interannually and can s

the effect of spatial variability in overland flow on the downslope pattern of soil loss on a semiarid hillslope southern arizona summary in this study we investigate the relation between soil loss and slope length in an interrill portion of a gentle plan planar semiarid hillslope in southern arizona simulated rainfall experiments were conducted on an 18 m wide by 35 m long runoff plot the upper end of which coincided with the hillslope divide sediment loads were measured at two cross sections s1 and s2 located 12 5 and 21 m respectively downslope from the divide from these data section soil losses under equilibrium runoff conditions were computed average section soil loss was found to increase from the divide to s1 and to decrease from s1 to s2 to explain this downslope pattern of soil loss a simulation model was developed for soil detachment by raindrop impact and sediment removal by overland flow at a cross section input data for the model consist of overland flow depths and velocities measured at closely spaced points along a cross section the model was applied to three cross sections located at 3 3 12 5 and 21 m downslope from the divide and predicted a downslope pattern of soil loss similar to that observed the success of the model suggests that in the interrill portions of a wide range of gentle arid and semiarid hillslopes downslope patterns of soil loss are controlled in large part by downslope changes in across slope distributions of overland flow depth and velocity

minimizing the grid resolution dependence of flow routing algorithms for geomorphic applications the results of flow routing methods currently used in the geomorphic literature depend on grid resolution this poses a problem for landscape evolution models which must be independent of grid resolution to the greatest extent possible here i illustrate a refinement of currently used flow routing algorithms that yields unit contributing areas i e contributing areas per unit width of flow with minimal grid resolution effects i illustrate the application of this method in idealized topography in high resolution digital elevation models dems of real world topography and by integration into a landscape evolution model for ridge and valley topography the landscape evolution model produces grid resolution independent results in a more straightforward way than previous models for this type of landscape

streaming potential in volcanic rocks from mount pelee streaming potential and electric conductivity have been measured in a laboratory on 11 consolidated samples coming from five deposits of the different evolutionary stages of mount pelde volcano the streaming potential coupling coefficient ranges from 35 to 4905 mv mpa 1 and increases with increasing permeability this increase is mainly due to the dependency of rock effective conductivity with permeability the permeability of the samples varies from 0 146x10 12 to 34x10 12 m 2 the zeta potential at ph 7 and water conductivity of 2 1x10 4 s m l is relatively small for the majority of the samples it ranges from 4 to 19 rev according to water conductivity analysis on mount pel e streaming potential coupling coetficients of 25 to 406 mv mpa 1 can be expected for this volcano

mathematical modeling of whole landscape evolution abstract the mathematical modeling of landform evolution consists of two components the processes represented i e considered dominant in the model and the typically computer model representation of these processes this review discusses the current debates surrounding processes represented in landform evolution the potential impact on both evolving landforms and computer model structure is discussed issues specifically discussed include a the fundamental nature of mass conservation and the role of detachment and transport limited processes in mass conservation equations b the interaction between detachment and transport limitation in channels c the role of hillslope erosion and soil properties and their interaction with channel processes d the interactions with tectonics when applying these models at large scale e depositional structures and implications for paleo climatic interpretation f engineering applications of these models and g numerical issues in the computer imp

laboratory verification of submicron magnetite production in pseudotachylytes relevance for paleointensity studies abstract pseudotachylytes generally possess stable remanent magnetizations but the processes by which pseudotachylytes are magnetized remain poorly understood magnetic hysteresis and scanning electron microscope studies reveal that experimental frictional melting of granites produces dispersed submicron inclusions of weakly interacting pseudo single domain psd magnetite in artificial pseudotachylyte the magnetite inclusions are absent in the undeformed granite protolith and result from oxidation of fe in melt susceptible mafic minerals during the melt quenched event the pseudotachylytes acquired a stable thermal remanence in fine grained psd magnetites during the rapid cooling of the melt implying that fine grained magnetite has the potential for paleointensity determinations of contemporaneous magnetic fields with co seismic faulting in granitoids

characterization of the principal tidal current constituents on the texas louisiana shelf we analyzed 81 current meter records of varying lengths 3 to 30 months to describe the principal diurnal o1 k1 p1 and q1 and semidiurnal s2 m2 k2 and n2 tidal current constituents on the texas louisiana continental shelf the louisiana texas shelf physical oceanography program latex had 81 current meters at 31 sites and varying depths from april 1992 to december 1994 the local inertial period range across the shelf 24 4 hours to 26 2 hours and thermal diurnal cycling during the summer season make it difficult to estimate the diurnal tidal constituents dominant tidal modes on the shelf are k1 o1 and m2 absolute and relative energy contained in each tidal constituent varies with shelf location the northeast corner of the shelf near atchafalaya bay has the largest tidal currents with maximum surface current amplitudes at 3 m depth of about 9 cm s 1 while typical maximum tidal surface currents near the shelf break are between 1 and 2 cm s 1 for each of the k1 o1 and m2 components in general the surface tidal currents decrease in magnitude as water depth increases toward the shelf break although the semidiurnal components are amplified more at midshelf locations than the diurnal components examination of tidal ellipses at different depths suggests that the m2 tide has less vertical structure while the diurnal tides exhibit more shear particularly at the more shallow locations sea surface height constituents estimated at five locations along the texas louisiana coast are in agreement with historical values

implications of sediment flux dependent river incision models for landscape evolution 1 developing a quantitative understanding of the factors that control the rate of river incision into bedrock is critical to studies of landscape evolution and the linkages between climate erosion and tectonics current models of long term river network incision differ significantly in their treatment of the role of sediment flux we analyze the implications of various sediment flux dependent incision models for large scale topography in an attempt 1 to identify quantifiable and diagnostic differences between models that could be detected from topographic data or from the transient responses of perturbed systems and 2 to explain the apparent ubiquity of mixed bedrock alluvial channels in active orogens although certain forms of the various models can be discarded as inconsistent with morphological data we find that the relative intrinsic concavity indices of detachment and transport limited systems defined herein largely dictate whether the various models can be tied to distinctive steady state morphologies preliminary data suggest that no such diagnostic differences may exist and other methods must be developed to test models accordingly we develop and explore differences in the scaling behavior of topographic relief and the extent of detachment versus transport limited channels as a function of rock uplift rate that may allow discrimination among various models further we explore potentially diagnostic differences in the rates and patterns of transient channel response to changes in rock uplift rate in addition to general differences between detachment and transport limited systems our analysis identifies an interesting hysteresis in landscape evolution hybrid channels at the threshold between detachment and transport limited conditions are expected to act as detachment limited systems in response to an increase in rock uplift rate or base level fall and as transport limited systems in response to a decrease in rock uplift rate especially during postorogenic topographic decline the analyses presented set the stage for field studies designed to test quantitatively the various river incision models that have been proposed

electrical conductivity measurement of granulite under mid to lower crustal pressure temperature conditions summary we have developed a technique to measure electrical conductivity of crustal rocks with relatively low conductivity and complicated mineral components in order to compare with results given by magneto telluric mt measurements a granulite from hidaka metamorphic belt hmb in hokkaido japan at high temperature and pressure conditions was obtained the granulite sample was ground and sintered under the conditions similar to those of mid to lower crust we have observed smooth and reversible change of conductivity with temperature up to about 900 k at 1 gpa the results were consistent with the electrical conductivity structures suggested by the mt data analysis considering pore fluid conduction mechanism or the role of accessory minerals in the rock the mechanisms of electrical conductivity paths in dry or basic rocks should be reconsidered

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