limiting apparent resistivity values for dipping bed earth models consideration is given to some special features of normalized apparent resistivity nar curves resulting from the deployment of wenner electrode arrays on the surface above dipping earth structures limiting values of the potential are derived when a direct current source is located at points on the surface above a simple two region dipping bed earth model and their influence on corresponding nar curve characteristics is investigated particular attention is given to the exploitation of such features to provide a new and direct approach to model parameter estimation either as an alternative to traditional curve matching techniques or as a source of supporting information when other earth model characterization methods have been employed throughout the emphasis is on the single dipping bed model but application to more complex structures is discussed including examples of two dipping beds dipping dikes and more general tilted unconformities

a simple model of fjord and coastal circulation interaction abstract the dynamical interaction of a narrow fjord with a wind driven coastal regime is investigated using a linear two layer numerical model the coriolis acceleration is important in the coastal regime but assumed to he unimportant in the fjord dynamical because v 0 for a wide variety of wind conditions bottom topography and model parameters the wind forced coastal circulation with its geostrophic alongshore currants has a strong effect on the circulation within the fjord these geostrophic currents control the free surface and pycnocline displacement at the fjord mouth thereby strongly affecting fjord circulation this mechanism is an alternative to the classical idea of hydraulic control at the mouth by sills or constrictions model simulators also show that the free surface slope is a baroclinic effect and that alongshore and across shore winds affect the fjord differently alongshore winds produce flooding while up and down fjord winds simply sat up the surface we find that offshore win

a model of the thermal bar circulation in a long basin a thermal bar is defined here as a zone of descending water at or near the fresh water temperature of maximum density in the present study we model physical properties such as velocity temperature turbulent fluxes time of onset and migration speed of the thermal bar in an idealized basin unlike models using prescribed eddy viscosity and diffusivity coefficients our model uses a second order turbulence closure scheme to model mixing due to turbulence the only inputs in the calculation are the surface wind the surface heat flux and the initial state of the fluid numerical simulations of the resulting circulation are presented for flow in a long rotating basin under prescribed surface heat and wind conditions the results show the influence of the relative magnitudes of mechanical and thermal forcing on the circulation a comparison with field observations shows reasonable agreement between computed and measured bar migration speeds the time necessary for the formation of the bar is computed and is found to depend on the surface forcing

a mechanism governing the estuarine circulation in deep strongly stratified fjords the estuarine circulation in deep strongly stratified fjords is discussed it is argued that a two layer description of the stratification in the fjord is correct in very wide fjords wide compared to the width of the mouth and possibly also in narrow fjords with high runoff and or weak mixing a theory for the thickness and the salinity of the brackish layer in a wide fjord was earlier developed by the present author and published in swedish 1975 and it is presented here among other findings in that theory we may mention that the thickness of the brackish layer is primarily determined by the internal hydraulic control for high specific runoff runoff unit horizontal surface area of the fjord and weak mixing in the other extreme with low specific runoff and strong mixing the thickness of the brackish layer is found to be proportional to the monin obukhov length the circulation in not very wide fjords is also discussed it is found that recirculation in the brackish layer may be expected whereby a two layer description of the flow field breaks down at least locally a critical rayleigh number that seems to control the recirculation of brackish water within the fjord is found a theory for the density difference between the mouth and the head in the brackish layer in the fjord is developed from the critical rayleigh number condition it is found that this density difference normally is proportional to the density difference between the brackish water at the mouth and the underlying sea water provided that the river runoff is not too heavy and or the mixing is not too weak this prediction is confirmed by extensive measurements from the nordfjord

satellite observations of tidal upwelling and mixing in the st lawrence estuary satellite thermal images noaa 9 of the st lawrence estuary are used to confirm the existence of a persistent cold spot due to tidal upwelling at the head of the lower st lawrence estuary and to show that cold water may be found episodically up to 100 km downstream of the head this extended cold anomaly may exist in two spatial configurations one confined to near the south shore the other being centered over mid estuary we discuss the various physical agencies likely to contribute to the growth of this anomaly and conclude that wind internal tides and advection of cold water from the head region are the most significant

response of benthos to stress factors in holocene arctic fjord settings maktak coronation and north pangnirtung fjords baffin island canada maktak coronation and north pangnirtung fjords are situated on cumberland peninsula baffin island canada having a common freshwater source from the penny ice cap bottom photographs were examined to identify epifaunal trails and shallow endobenthic burrow openings exposed on the seafloor surface these were compared to biogenic sedimentary structures revealed through x radiograph images and direct observations of lehigh gravity core samples intermediate and deep tier structures characterize the ichnofabrics of the glaciomarine sediments extensive bioturbation by the shallow tier and epibenthic tracemakers most notably ophiuroid echinoderms brittlestars and other organisms has destroyed much of the primary sedimentary fabric i e lamination resulting in homogenous silty clay sediments the dominant deep tier structure consisting of an open three dimensional boxwork burrow system is the most pervasive biogenic structure observed within the core samples interestingly although proximal distal trends in benthic macrofaunal composition are evident in the bottom photographs ichnofabrics remain relatively constant along the length of the fjords environmental factors influencing the biological community in these modern high latitude fjords differ from conditions described in paleozoic and cenozoic fjord environments an increasing number of recent studies are expanding significantly on the fjord ichnology database and provide the basis for the revision of the currently proposed fjord trace fossil model accommodating the complexity and diversity of fjord settings

the comparison of a numerical model to observations of velocity and scalar data in burrard inlet and indian arm british columbia a laterally integrated time dependent numerical model of burrard inlet and indian arm is compared to time series of cyclesonde velocity and scalar data that have 10 m vertical resolution as long as deep water renewal is not occurring the model can reproduce the observed m2 and k1 tidal response in the basin of indian arm also although the rate of freshwater inflow into indian arm and burrard inlet is not large the simulated tidal response is noticeably improved if freshwater inflow is taken into account when deepwater renewal is observed to occur the model also simulates renewal but it does so poorly and the ability of the model to accurately simulate the m2 and k1 tide degrades significantly

baroclinic annular variability of internal motions in a patagonian fjord time series of horizontal velocities echo intensity wind velocity and atmospheric pressure were collected for 200 days in a patagonian fjord to explore pycnocline motions produced by the southern hemisphere s baroclinic annular mode bam the bam variability occurs between 20 and 30 days and is associated with fluctuations in atmospheric kinetic energy and in turbulent fluxes of heat spectra of horizontal velocities and normalized echo intensity in the fjord s water showed highest energy between 25 and 30 days this was explained by sustained westerly winds associated with extreme low pressure systems 900 hpa that had periodicity related to the bam wind forcing produced 40 cm s 1 along channel and cross channel currents in the surface layer which in turn created a wind induced setup toward the head of the fjord the setup was accompanied by a deepening of the pycnocline from 5 to 15 m depth with 25 to 30 day periodicity as derived from the normalized echo intensity the dominant empirical orthogonal function mode of the normalized echo intensity profiles explained 70 8 of the variance and also exhibited a 25 30 day periodicity further a wavelet and spectral analysis of 10 years of atmospheric pressure indicated peaks between 25 and 30 days each year indicating that the bam consistently influences weather patterns in chilean patagonia this is the first documented case of baroclinic annular variability in a specific region of the southern hemisphere and of its effects on fjord systems

sedimentary processes of canadian arctic fjords abstract conceptual models of circulation and sedimentation in arctic fjords are presented to illustrate the current understanding of these environments circulation is a vigorous process in these fjords and is enhanced by the loss of the freshwater cap during the long winter period of near zero inflow the process of brine rejection during the formation of sea ice and the role of glaciers and icebergs injecting freshwater at depth on the other hand the presence of sea ice blocks reduces the mixing action of wind which may otherwise represent the largest input of energy to fjord circulation it also provides a freshwater layer on melting and may in some circumstances damp the amplitude of tides during summer large loads of glacial sediment entering arctic fjords are separated into streams of overflowing suspended load and bed load in the presence of salt water as the concentrations of suspended load in the freshwater are normally much less than required to overcome the density of the salt water deposition occurs throughout the fjord by rapid settling of flocculated particles from the overflowing brackish water and from grain flows in the proximal environment created as the fluvial traction carpet moves over the delta foreset slope after sediment has been deposited it may be remobilized by slides which in turn may develop into fully turbulent flows as they move down the fjord floor a range of deposits from slump debris to minor turbidites are postulated to occur with the flocculated muds although not all have yet been examined in the arctic fjord stratigraphic record sea ice is an important sedimentological agent in arctic fjords it passively carries fluvial aeolian and colluvial material which is subsequently released from the ice during the stage of puddle draining at break up sea ice also actively incorporates fine and coarse sediments up to large boulders during freezing along the shores in winter and by wave and tidal current washing controlled by the presence of the ice during break up

double diffusive convection in this paper we present a rather personal view of the important developments in double diffusive convection a subject whose evolution has been the result of a close interaction between theoreticians laboratory experimenters and sea going oceano graphers more recently applications in astrophysics engineering and geology have become apparent in the final section we attempt to draw some general conclusions and suggest that further progress will again depend on a close collaboration between fluid dynamicists and other scientists

sedimentary organic matter geochemistry of clayoquot sound vancouver island british columbia surface sediment samples from three interconnected fjords of clayoquot sound british columbia were density fractionated 1 6 g cm 3 to isolate discrete organic debris od from mineral associated organic matter mom total organic carbon oc values varied greatly ranging from 0 1 to 8 8 by weight with a general decreasing trend from fjord head to the continental shelf within the sediment terrestrial om was present either as vascular plant debris or soil mom down fjord the woody vascular plant material in the od fraction acquires nitrogen which is hypothesized to be due to the bacterial incorporation of nitrogen from the water terrestrial oc in the mom is incompletely replaced by marine oc within the fjords resulting in a 65 net loss of mom sediments deposited under oxic and intermittently anoxic water column conditions have organic carbon to surface area ratios oc sa ranging from 0 4 to 1 2 mg c m 2 similar to that of typical continental margin sediments given that temperate fjords contain an estimated 12 of the continental margin sediment deposited during the last 100 000 yr and that they bury at least a margin equivalent amount of oc either weight or surface area normalized we hypothesize that temperate fjords may contain 12 or more of the sedimentary oc buried during this time

a numerical model of stratified circulation in indian arm british columbia a laterally integrated numerical model has been developed for the study of stratified circulation in inlets the model is time dependent and includes advective terms horizontal and vertical turbulent diffusion of momentum and salt and variations in width and depth initial and boundary conditions based on winter measurements in burrard inlet and indian arm were used to study the inlet s response to tidal forcing the friction term was tuned to match calculated and observed dissipation rates evidence for a standing wave pattern in the response of the m2 and k1 tidal constituents is discussed a comparison of model results with cyclesonde current meter time series at two locations in indian arm is consistent with resonance a modal decomposition of the calculated response shows that most of the energy is contained in the barotropic and first baroclinic modes with the former dominating near the sill and the latter dominating in the deep basin second mode energy was significant for the k1 at some locations

polarization of crack waves along an artificial subsurface fracture we analyze three dimensional 3d particle motions of crack waves which propagate along a fracture to determine fracture orientation crack waves were measured at an artificial subsurface fracture at a depth of approximately 370 m in the higashihachimantai hot dry rock model field in japan dispersion was observed in crack waves velocities of crack waves below 100 hz are 100 m s 150 m s along this artificial fracture therefore crack waves arrived after compressional wave and shear wave a coherence matrix is used to analyze the 3d particle motions in the frequency domain noise which is outside of the band of the detector is excluded in the coherence matrix analysis we examine the polarization of 3d particle motions of crack waves using principal component analysis the longest axis of an ellipsoid which approximates the 3d particle motions shows a direction consistent with estimates obtained by core sample measurements and tectonic stress measurements the differences in fracture orientation obtained from the crack wave analysis and the core sample analysis are less than 16 in azimuth and less than 20 in dip

seasonal mixing processes in an arctic fjord system abstract studies of water movement in the aafardlikavs qaumarujuk fjord system in west greenland have barn carried out in order to understand the movement of mine tailings discharged into agfardlikavs fjord observations are explained in terms of resonance of the internal tide deep convection associated with sea ice growth and basin water exchange occurring at the time of ice breakup in early summer mixing processes are dominated by these events illustrating the limitations of any seasonal description based on conventional diffusive processes

the internal tide and resonance in indian arm british columbia the nature of the internal tide in indian arm is discussed in the winter of 1983 1984 this internal tide was observed to change from a predominantly m2 internal response to a predominantly k1 one this change in the response is explained as a partial resonance response of the system during the 1983 1984 winter the resonance period steadily increased from 14 hours at the start to 22 hours at the end it is suggested that the enhanced internal response at the k1 frequency late in the winter is due to resonance the fitting of normal modes was done to look at the energy flux in indian arm about 20 30 of the energy flux is found to return from the head of the inlet a finding supporting the resonance hypothesis which requires energy to be reflected from the head

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

differentiating anisotropy and lateral effects using azimuthal resistivity offset wenner soundings azimuthal resistivity surveys increasingly are being used by hydrogeologists in the identification and characterization of fractured rocks in these investigations electrical resistivity is measured as a function of azimuth about a fixed central point in most recent published examples any observed change in apparent resistivity with azimuth is interpreted as being indicative of fracture anisotropy however interpretation of rotational sounding data is actually more complicated as azimuthal variations in apparent resistivity are also produced by the presence of dipping stratigraphy and other lateral changes in formation resistivity such effects are generally overlooked because the field techniques normally employed are incapable of detecting them consequently it is quite probable that the results of many published surveys have been wrongly interpreted an alternative field procedure and interpretation methodology has been developed to differentiate anisotropy dipping layers and lateral effects this approach makes use of the offset wenner technique and examines the different responses of the individual wenner resistances above different geological structures analysis of data obtained using the azimuthal offset wenner technique from sites in britain and ireland have successfully identified subsurface structures and determined the anisotropy where it is present

vertical mixing rates in fjords determined using radon and salinity as tracers excess radon profiles were measured in several washington state and british columbia fjords generally exponential profiels were observed during periods of bottom water stagnation values of the vertical eddy diffusivity were estimated from the exponential excess radon profiles and from salinity changes in the stagnant bottom water these values ranged from 0 16 to 36 cm2 s 1 among fjords and the variation could be explained by different inputs of tidal energy into vertical mixing for the different fjords excess radon was also observed in surface water of several fjords the source of this excess radon was the freshwater runoff entering the fjords values of the vertical eddy diffusivity were estimated for the near surface water of narrows inlet from these profiles to be 0 32 to 0 47 cm2 s 1 across the freshwater saltwater interface and 0 9 to 3 1 cm2 s 1 between 5 and 35 m depth

where glaciers meet water subaqueous melt and its relevance to glaciers in various settings glacier change is ubiquitous but the fastest and largest magnitude changes occur in glaciers that terminate in water this includes the most rapidly retreating glaciers and also several advancing ones often in similar regional climate settings furthermore water terminating glaciers show a large range in morphology particularly when ice flow into ocean water is compared to that into freshwater lakes all water terminating glaciers share the ability to lose significant volume of ice at the front either through mechanical calving or direct melt from the water in contact here we present a review of the subaqueous melt process we discuss the relevant physics and show how different physical settings can lead to different glacial responses we find that subaqueous melt can be an important trigger for glacier change it can explain many of the morphological differences such as the existence or absence of floating tongues subaqueous melting is influenced by glacial runoff which is largely a function of atmospheric conditions this shows a tight connection between atmosphere oceans and lakes and glaciers subaqueous melt rates even if shown to be large should always be discussed in the context of ice supply to the glacier front to assess its overall relevance we find that melt is often relevant to explain seasonal evolution can be instrumental in shifting a glacier into a different dynamical regime and often forms a large part of a glacier s mass loss on the other hand in some cases melt is a small component of mass loss and does not significantly affect glacier response

sill processes related to deep water renewal in a fjord observations of the gravitational circulation over the sill at the entrance to puget sound indicate a fortnightly modulation of the two layer flow with a corresponding variation in stratification gravitational circulation and stratification reach a maximum during neap tides and a minimum during spring tides the modulation appears to be a function of the turbulence generation by tidal flow over the sill which varies as a function of tidal amplitude the enhanced gravitational circulation during neap tides augments the flux of dense water across the sill region and episodes of bottom water renewal in puget sound result intrusions of dense water in the main basin of the sound show a fortnightly periodicity with a phase lag appropriate for the propagation of an internal bore from the sill region commencing at the neap tide observations indicate that the intrusions take the form of gravity currents propagating at approximately 20 cm s 1 down the main basin the detailed dynamics of the turbulent mixing processes that modulate the onset of inflow were not resolved in this study but the integrated effect of tidal mixing on the low frequency circulation is clearly demonstrated

the deepwater exchange cycle in indian arm british columbia abstract a silled fjord on the british columbia coast indian arm was used to study the exchange processes controlling deepwater exchange in fjords bottom water renewal took place during the winter of 1984 85 hydraulic control of the exchange is exerted over the long sill which restricts access to the fjord the maximum density at the sill occurs during neap tides no distinct peaks in the velocity at the sill are observed during periods of inflow reduced vertical mixing over the long sill during periods of neap tides sets the timing of the bottom water exchange during each inflow over the 1984 85 winter about 20 of the water in the fjord was replaced these exchanges occurred over periods of 5 10 days between the exchange years diffusion of the water in the basin is important in conditioning the water for the next exchange event the vertical diffusion coefficient k t was determined from an analysis of the salinity data and was found to be related to the buoyancy frequency n by the relationship k v n 1 6

elastic interface waves along a fracture non welded interfaces can be treated as a displacement discontinuity characterized by elastic stiffnesses applying this boundary condition to a generalized rayleigh wave it is shown that a fast and a slow dispersive wave can propagate along the fracture even when the seismic properties of the rock on each side are identical

evaluation of the three dimensional configuration of a subsurface artificial fracture by the triaxial shear shadow method we have determined the three dimensional configuration of a single fracture in the hot dry rock model field at higashi hachimantai japan by the triaxial shear shadow method the crack was created by hydraulic fracturing in intact welded tuff at a depth of 370 m we have carried out crosshole seismic measurements by using a downhole air gun and a triaxial seismic detector extinction at a special polarization direction and the dependency of transmissivity in shear wave component on incident angle were determined by a triaxial hodogram analysis of detected signals we have evaluated the orientation and distribution of the fracture using the shear wave extinction and the three dimensional configuration of the fracture by a continuation of the evaluated orientations the results are in good agreement with the data obtained by independent experiments in the field

assessment of the reliability of 2d inversion of apparent resistivity data the reliability of inversion of apparent resistivity pseudosection data to determine accurately the true resistivity distribution over 2d structures has been investigated using a common inversion scheme based on a smoothness constrained non linear least squares optimization for the wenner array this involved calculation of synthetic apparent resistivity pseudosection data which were then inverted and the model estimated from the inversion was compared with the original 2d model the models examined include i horizontal layering ii a vertical fault iii a low resistivity fill within a high resistivity basement and iv an upfaulted basement block beneath a conductive overburden over vertical structures the resistivity models obtained from inversion are usually much sharper than the measured data however the inverted resistivities can be smaller than the lowest or greater than the highest true model resistivity the substantial reduction generally recorded in the data misfit during the least squares inversion of 2d apparent resistivity data is not always accompanied by any noticeable reduction in the model misfit conversely the model misfit may for all practical purposes remain invariant for successive iterations it can also increase with the iteration number especially where the resistivity contrast at the bedrock interface exceeds a factor of about 10 in such instances the optimum model estimated from inversion is attained at a very low iteration number the largest model misfit is encountered in the zone adjacent to a contact where there is a large change in the resistivity contrast it is concluded that smooth inversion can provide only an approximate guide to the true geometry and true formation resistivity

evaluation of landfill disposal boundary by means of electrical resistivity imaging this paper deals with an employment of electrical resistivity imaging eri for survey of leachate content on the waste disposal site in northern israel the research consisted of conducting ten eri lines and drilling investigation wells data simulation used a 2d earthimager inversion program analysis of 2d eri interpretation results shows that determination of the boundary between the landfill body bottom intensively saturated with leachates and underlying layers of highly water saturated fat nonconsolidated clays presents a challenge however statistical analysis of eri data indicates that standard deviation and confidence interval of a set of resistivity data measured in the landfill body are significantly larger than those in underlying clays moreover maximum changes of these parameters are found on the boundary between landfill body and underlying soil thus reflecting natural differences in scattering of resistivity data measured in these two objects

the offset system of electrical resistivity sounding and its use with a multicore cable abstract one of the most troublesome problems in resistivity sounding is caused by the spurious effects of near surface lateral resistivity variations it has been found that the effects can be strongly reduced by measuring earth resistances at two electrode array positions such that in one position the lateral effect is a positive contribution to the total measured signal and in the other the contribution is negative the subsequent combination of the two measurements virtually eliminates the lateral effect the same technique can also result in a significant reduction in the total number of necessary electrode positions consequently the method can be used with a multicore cable system in this way in addition to improving the accuracy of the measured results time and manpower are considerably reduced details of the method examples and comparisons with traditional sounding techniques are given

crack stiffness from crack wave velocities we estimate crack stiffness by analyzing crack wave velocities we measured crack waves which propagated along an artificial subsurface fracture in higashi hachimantai hot dry rock model field iwate prefecture japan the artificial subsurface fracture was created at a depth of about 370 m by hydraulic fracturing we controlled contact conditions of the fracture surfaces by hydraulic pressurization a time frequency representation technique the pseudo wigner distribution is applied to determine the travel time of the crack wave the crack wave shows dispersion low frequency components below 100 hz have lower velocities we compare velocity data obtained in the field crack wave measurement to those calculated in a simple fracture model in which dimensionless crack stiffness reflects a degree of contact of the asperity on the fracture surfaces slope of the dispersion estimated from the field data agrees with that of the theoretical curves we estimate the dimensionless crack stiffness is 0 001 to 0 005 from this comparison this dimensionless crack stiffness 0 001 means that crack stiffness on propagation path of the crack waves is 74 gpa m

dispersion analysis of crack waves in an artificial subsurface fracture using two crack models the authors investigated crack wave dispersions in an artificial subsurface fracture both experimentally and numerically using a wavelet analysis and two crack models crack waves are seismic modes that propagate along a fracture the dispersion characteristics of crack waves depend on the geometry and physical properties of a fracture the authors measured crack waves at an artificial subsurface fracture in higashi hachimantai hot dry rock model field japan this subsurface fracture is at a depth of about 370 m during a measurement they injected water into the fracture and changed the interface conditions of the fracture a wavelet analysis provided the dispersion of the arrival times of crack waves the crack waves showed positive velocity dispersion i e low frequency components arrived later as wellhead pressure increased due to water injection the dispersion characteristics changed a low velocity layer lvl model and a crack stiffness model were examined to explain crack wave dispersion in the lvl model rock layers with a low velocity surround a fluid layer there is no contact between the lvls on the other hand the crack stiffness model considers crack stiffness due to contact between asperities on fracture surfaces the arrival time curves calculated by the crack stiffness model showed a good fit to the measured values as wellhead pressure increased crack stiffness decreased and thickness of a fluid layer increased in contrast the lvl model did not adequately duplicate the measured data

a tide generated internal waveform in the western approaches to the strait of gibraltar aircraft expendable bathythermograph radar infrared scanner and visual data collected in october 1982 1984 and 1985 as well as space shuttle photographs indicate that an internal waveform depending on flow conditions either an internal hydraulic jump or a lee wave is a semipermanent feature over the camarinal sill in the western approaches to the strait of gibraltar comparison of these data with both historic and recent current meter mooring data indicates that the waveform generated at the interface between the atlantic and mediterranean waters undergoes periodic changes wrought by interaction of the tidal current and the flow of the atlantic and mediterranean waters we believe that the waveform is a major mixing mechanism between the two water masses