effect of salt exclusion from lake ice on seasonal circulation we describe the circulation of tailings lake located 220 km north of yellowknife northwest territories canada from jul 2004 to sep 2007 temperature and conductivity profiles were collected together with data from three moored temperature chains and a meteorological station the salt content of the lake was elevated salinity 1gl 21 relative to surrounding natural waters 0 1 g l21 winter ice cover included 60 80 cm of transparent black ice which excluded up to 99 of the salt from the water as the ice formed during winter the salt excluded from the ice was mixed throughout the water column under the ice in spring ice melt and snow runoff resulted in a freshwater cap the density contrast between this fresh epilimnion and the more saline hypolimnion was sufficient to inhibit spring turnover in summer the epilimnion was deepened by storms mixing anoxic water from the hypolimnion into the surface layer because spring turnover was suppressed oxygen replenishment of the hypolimnion occurred only in fall although tailings lake has been subject to numerous anthropogenic changes similar effects can be expected in other natural and manmade water bodies with elevated salinity and significant ice cover

the initial response of a stratified lake to a surface shear stress laboratory experiments are used to study the initial response of a stratified fluid to the action of a wind stress the experiments are described in the context of a parameterization scheme that quantifies the strength of the applied stress relative to the bulk stability of the fluid and also the duration of the wind stress relative to the periods of the waves generated by the stress this study concentrates on the first fundamental internal wave period in experiments where the fluid is considered to have upwelled i e the stratified region of the fluid reaches the surface at the upwind endwall the majority of the experiments use three layer initial density profiles as an approximation to a continuously stratified water column a linear model using normal modes proved successful prior to the commencement of upwelling and this enabled an estimate to be made of the time at which upwelling occurred at this point the wave development ceased and the flows developed via entrainment mechanisms consideration of the energy budget showed that little of the input energy was stored in the system the initial mixing efficiency defined as the ratio of the mean potential energy gained to the energy imparted by the belt never exceeded 30 peak efficiency occurred when the surface stress was just sufficient to bring the interfacial region to the surface

modal response of reservoirs to wind stress an analysis of the response of a density stratified reservoir to surface shear stress is presented the reservoir is assumed to be two dimensional and to have a constant depth in the limit that the bulk wedderburn number wb and the bulk richardson number rib are both infinite the resulting equations are linear and solutions can be found in terms of the individual responses of a set of orthogonal normal modes for the case of a steady wind stress the solution consists of periodic motions and steady isopycnal displacements however the steady state isopycnal slope at the base of the mixed layer is infinite implying that upwelling can occur when the wedderburn number is quite large this is attributed to blocking of the stratified fluid below the mixed layer by the endwall the modal theory presented in this paper is compared with experimental observations made using a belt to impart shear stress to a stratified fluid contained in a box the comparison shows that the present theory is qualitatively corr

internal waves in a small reservoir horizontally distributed temperature time series recorded in the thermocline of a small reservoir during autumn are used to identify both basin scale and higher frequency internal waves stationary and nonstationary spectral analyses are used to identify dominant frequencies the horizontal distribution of data allows a map of the basin scale wave energy to be determined three layer normal mode modeling incorporating damping emulates the basin scale behavior well this provides estimates of velocity shear and hence the internal stability the nonstationary frequency analysis identifies times of high frequency internal wave activity wave periods of 2 10 min this is definitely linked to the basin scale wave driven shear and hence to deceases in stability estimates of dissipation for the thermocline and hypolimnion are 3 10 8 and 6 10 9 m 2 s 3 respectively the inferred variability in the hypolimnetic value is demonstrated

baroclinic effects on wind driven lateral circulation in chesapeake bay abstractthe 2 month long mooring data were collected in a straight midsection of chesapeake bay to document the lateral circulation driven by along channel winds under upestuary winds the lateral circulation featured a clockwise looking into estuary circulation in the surface layer with lateral ekman forcing as the dominant generation mechanism under downestuary winds however the lateral circulation displayed a structure dependent on the wedderburn number w a counterclockwise circulation at small w and two counterrotating vortices at large w the surface lateral velocity was phase locked to the along channel wind speed analysis of the streamwise vorticity equation showed that the strength and structure of the lateral circulation in this stratified estuary were largely determined by the competition between the tilting of planetary vorticity by along channel currents and lateral baroclinic forcing due to sloping isopycnals under strong downestuary winds the lateral baroclinic forcing offset or

hydrologically induced slope deformations detected by gps and clinometric surveys in the cansiglio plateau southern alps abstract changes in groundwater or surface water level may cause observable deformation of the drainage basins in different ways we describe an active slope deformation monitored with gps and tiltmeter stations in a karstic limestone plateau in southeastern alps cansiglio plateau the observed transient gps deformation clearly correlates with the rainfall both gps and tiltmeter equipments react instantly to heavy rains displaying abrupt offsets but with different time constants demonstrating the response to different catchment volumes the gps movement is mostly confined in the horizontal plane ssw direction showing a systematic tendency to rebound in the weeks following the rain four gps stations concur to define a coherent deformation pattern of a wide area 12 5 km 2 concerning the whole southeastern slope of the plateau the plateau expands and rebounds radially after rain by an amount up to a few centimeters and causing only small vertical deformation the effect is largest where karstic features are mostly developed at the margin of the plateau where a thick succession of cretaceous peritidal carbonates faces the venetian lowland a couple of tiltmeters installed in a cave at the top of the plateau detect a much faster deformation that has the tendency to rebound in less than 6 h the correlation to rainfall is less straightforward and shows a more complex behavior during rainy weather the different responses demonstrate a fast hydrologic flow in the more permeable epikarst for the tiltmeters drained by open fractures and fissures in the neighborhood of the cave and a rapid tensile dislocation of the bedrock measured at the gps stations that affect the whole slope of the mountain in the days following the rain both tiltmeter and gps data show a tendency to retrieve the displacement which is consistent with the phreatic discharge curve we propose that hydrologically active fractures recharged by rainfall are the most likely features capable to induce the observed strain variations

an experimental study of the upwelling response of stratified reservoirs to surface shear stress an experimental study of the dynamic response of non rotating stratified reservoirs to the application of surface shear stresses is presented the experiments were made using two layered and linear stratifications a moving belt was used to supply a shear stress to the fluid detailed measurements of the density field show that upwelling occurs at all values of the wedderburn number w rather than only occurring when w 1 differences between the two layer theory and the present observations are attributed to the fact that the experimental stratifications were continuous rather than layered shearflow dispersion is observed to be an important mechanism for distributing the effects of localized upwelling over the entire length of the mixed layer a model of mixed layer deepening based on upwelling and shearflow dispersion is presented and is compared to the observations of this and other experimental studies

lateral circulation and sediment transport driven by axial winds in an idealized partially mixed estuary 1 a 3d hydrodynamic model roms is used to investigate lateral circulation in a partially mixed estuary driven by axial wind events and to explore the associated transport of sediments the channel is straight with a triangular cross section the model results suggest that driving mechanisms for lateral circulation during axial wind events are different between stratified and unstratified conditions when the water column is largely unstratified rotational effects do not drive significant lateral circulation instead differential advection of the axial salinity gradient by wind driven axial flow is responsible for regulating the lateral salinity gradients that in turn drive bottom divergent convergent lateral circulation during down up estuary winds from the subtidal lateral salt balance it is found that the development of lateral salinity gradient by wind induced differential advection is largely counterbalanced by the advection of salt by lateral circulation itself when the water column is stratified the lateral flow and salinity structures below the halocline closely resemble those driven by boundary mixing and rotational effects are important lateral sediment flux and the event integrated sediment transport are from channel to shoals during down estuary winds but reversed for up estuary winds potential impacts of wind generated waves on lateral sediment transport are evaluated with two cases representing event conditions typical of upper chesapeake bay accounting for wind wave effects results in an order of magnitude increase in lateral sediment fluxes because of greater bottom stresses and sediment resuspension

wind induced entrainment in a stably stratified fluid experiments on mixed layer deepening in a straight wind flume initially containing a two layer fluid were carried out in order to simulate an effectively unlimited water body or a situation where the presence of end walls is not yet noticeable the water from the upper layer was withdrawn at the downstream end and supplied again at the upstream end in part of the experiments upper layer depths and mean density and mean velocity profiles were measured for overall richardson numbers based on the surface friction velocity ranging from 22 to 1090 gradient richardson numbers in the transition layer between the mixed layer and the undisturbed layer and in the mixed layer were estimated the correction of the results for the effects of recirculation is discussed

surface deformation associated with a dipping hydrofracture crustal deformation associated with hydrofracture is modeled by a dipping rectangular dislocation beneath the surface of an elastic half space the burger s vector is taken normal to the rectangular surface analytical expressions for vertical displacements are obtained from integration of volterra s equation by using mindlin s point force solutions for the elastic halfspace in the limits of 0 and 90 dip the results agree with those obtained by maruyama 1964 for poisson s ratio 0 25 expressions for arbitrary poisson s ratio are given for elongate dislocations the displacement field agrees with curves given by pollard and holzhausen 1979 for two dimensional near surface fractures at various dips at dip 0 a deep square dislocation gives displacements indistinguishable from those of sun s 1969 model of a horizontal penny shaped crack beneath the surface of an elastic half space modifying his result for shallow depths shows that they correspond to a dislocation of semi elliptical cross section with the surface displacement field asymptotically approaching a semi elliptical shape as depth decreases to zero similarly the surface displacement field of the square dislocation approaches that of its rectangular cross section nonlinear inversion of surface tilt fields associated with hydrofracture of deep boreholes gives estimates of fracture geometry position and orientation along with their uncertainties two examples are presented one of a near horizontal and one of a near vertical fracture

formulae for pressure gradients in one dimensional lake models formulae for barotropic and baroclinic pressure gradients suitable for one dimensional lake models are derived and explored the derivation is based on the equation for free standing oscillations and a continuity relation the formulae which are easy to derive and use give the correct external and internal seiche frequencies for nonrotating rectangular one or two layered basins of constant depth when applied to situations with continuous stratification further assumptions need to be introduced these are discussed in the paper applications to a laboratory experiment dealing with wind induced entrainment show that pressure gradients for the entrainment process are significant and that the pressure formulae derived capture this effect the formulae are also used in combination with a one dimensional lake model comparisons with field measurements of the seasonal stratification show that the inclusion of pressure gradients improves the predictive capabilities of the lake model

stability and meromixis in a water filled mine pit a field experiment examined stability and stratification in a disused mine fit filled with 1 75 x lo7 m3 of water vertical profiles of conductivity and temperature indicated that due to substantial chemical stratification spring and autumn overturn did not penetrate to the base of the pit although parameterization indicated that double diffusion should be expected we found only circumstantial evidence of associated step structure the available data suggest that groundwater inflow created a warm salty pool of water at the base of the water column giving the appearance of a meromictic structure with a monimolimnion however this pool was noi a consistent feature suggesting both a variable inflow and significant diffusion rates from the temperature data estimates indicated that hypolimnetic vertical eddy diffusivity varied between 1 x 10e7 and 5 x lo m s l the observations identify short term relatively energetic internal wave events that may have a significant impact on this value the present study is useful in two ways first it shows how pit lakes form a natural laboratory fcr a range of processes and second it illustrates how these processes relate to diffusion paranieterization it is clear that reliable parameterization is vital for long term modeling required for prediction of water quality over decadal timescales with the closure of an open cut mining operation come the dual problems of rehabilitation of the mine pit and containment of deleterious material generated by the mine during its life in many cases the pit fills with water either naturally or through mine activities thus an artificial lake of moderate volume is created davis and ashenberg 1989 characterization of the transport processes within the water column is important for two reasons first the pit is likely to contain hazardous levels of dissolved metals and second if vertical transport rates are low then the pit may prove suitable as a storage location for hazardous material water filled mine pit lakes pit lakes have received consideration in the literature but with a biological or geochemical emphasis e g klapper and schultz 1995 crater lakes are the natural system most similar to these artificial water bodies martin 1985 macintyre and melack 1985 pit lakes are unique for several reasons they are often deep relative to natural lakes of similar surface area they have high surrounding walls that often generate a microclimate different to that outside the pit they typically have very thin sediment layers they may undergo substantial and rapid changes in water level and they are likely to contain significant concentrations of dissolved material the final point is important if the dissolved material is environmentally harmful or if it leads to meromixis with these departures from what might be associated with typical natural lakes

displacement of surface monuments vertical motion several measurements of vertical ground motion at pinon flat observatory california indicate the overall weakness and instability of the earth s weathered surface with respect to the underlying rock cumulative long period motions of order 0 5 mm per year dominate these records though smaller elastic deformations caused by precipitation loading atmospheric loading and tidal strains are evident at higher frequencies all of these help to characterize the near surface material the long period records suggest that near surface weathering is the dominant influence on monument motion at least at this site on crystalline rock in a semi arid environment rainfall loading gives an average vertical modulus of 2 6 gpa for the material in the uppermost 26 m of the ground compared with 88 gpa for granite under moderate confining stress atmospheric loading gives similar results but indicates the ground is permeable to airflow at periods longer than a few hours earth tide records show poisson s ratio to be 0 09 in contrast to the normative range of 0 2 0 25 establishing that horizontal strains couple only weakly into vertical ones so that vertical strains near the surface are a poor measure of areal strain the form of the ground surface displacement power spectrum indicates that analyses of geodetic surveys would be improved with the inclusion of a monument positioning error budget that increases with time because of ground instability and the generally small rate of crustal tectonic motions deeply emplaced monuments will be needed for observational programs designed to detect short term changes in crustal deformation over baselengths of order 10 km and less

shelf fjord exchange driven by coastal trapped waves in the arctic in this article we show that the class of low frequency subinertial waves known as coastal trapped waves ctws are a significant agent of water volume exchange in a west svalbard fjord and by extension more widely along the west svalbard and east greenland margins where similar conditions prevail we show that ctws generated by weather systems passing across the sloping topography of the shelf break propagate into the fjord steered by the topography of an across shelf trough the ctws have characteristic periods of 2 days set by the passage time of weather systems phase speeds and wavelengths vary seasonally by a factor of two according to stratification winter summer values are cp 0 25 ms 1 0 5 ms 1 and 40 km 84 km ctw induced flow velocities in excess of 0 2 ms 1 at 100 m water depth are recorded observationally scaled ctw model results allow their explicit role in volume exchange to be quantified of the estimated exchange terms estuarine exchange is weakest qest 0 62 103 m3s 1 followed by barotropic tidal pumping qbt 2 5 103 m3s 1 with intermediary exchange dominating qi 2 4 104 m3s 1 oscillatory flows display greatest activity in the 1 5 day period band and ctw activity is identified as the likely source of variability in the 40 60 h period band within that band intermediary exchange driven by ctws is estimated as qictw ave 0 82 104 m3s 1 an exchange rate exceeding both barotropic and estuarine exchange estimates

an extraordinary upwelling event in a deep thermally stratified lake 1 a unique combination of temporal and spatial measurements provides a description of an extraordinarily large upwelling event in lake tahoe ca nv the 4 d event which engulfed half of the lake s surface and had an amplitude of 500 m was recorded with in situ and space borne instruments the vertical mixing that ensued was characterized by a large transfer of heat across the thermocline resulting in the replacement of the distinct two layer thermal structure by a diffuse temperature gradient prior to the event mixing energy due to the cooling flux at the surface was two orders of magnitude larger than the mixing energy associated with the wind this dominance by cooling yielded the two layer structure during the event wind energy was of similar magnitude to the cooling energy the large bottom velocities that were produced at the end of the event were sufficient to re suspend sediment into the water column

wind induced exchange at the entrance to concepcion bay an equatorward facing embayment in central chile abstract hydrographic and underway water velocity profiles were measured at the entrance to concepcion bay an equatorward facing embayment in central chile in order to illustrate the wind induced exchange flow observations took place over a 25 h period 5 6 january 2002 during the austral summer which is characterized by upwelling winds in the region one portion of the observational transect was directly influenced by the wind and the other was protected from such influence by an island the portion of the transect influenced by wind showed a surface layer delimited by a pycnocline moving downwind owing to the direct action of wind stress this surface transport should have caused an onshore decrease of surface elevation that would drive upwind flow below the surface layer the portion of the transect protected by the island was influenced by its wake and perhaps forced by a semidiurnal tide this study is one of the few observational examples of wind induced flow that documents the wind induced exchange pattern under weak internal friction low ekman number this pattern consists of downwind flow in an upper layer delimited by the pycnocline and upwind flow below

borehole tilt measurements aperiodic crustal tilt in an aseismic area abstract nine months of tilt measurements at tidal sensitivity with an askania tiltmeter at a depth of 12m show aperiodic tilts with time scales of two days and upwards statistically significant correlations are found with meteorological variables and in particular with variations in the local groundwater table typically a variation in the tilt of 1 microradian is associated with a variation in the groundwater table of about 1 m the seasonal variation over the last two years in groundwater has a range of 3 m about a mean level approximately 2 5 m below the ground surface these variations have been continuously measured by a neyrpic tide gauge in a 50 m uncased borehole in addition to this seasonal variation are episodic events some in excess of 1m associated with heavy rainfall 2 3 cm these events have a rapid onset lasting 1 day followed by a decay lasting 10 days or more tilt events associated with similar groundwater variation could in a seismic region be easily mistaken for precursory tilt and this work emphasises the necessity of taking a complete account of meteorology in seismic zones where strain and tilt measurements are in progress further work is in progress with the askania tiltmeter which is now installed in an adjacent borehole at a depth of 30 m and a hughes tm 3 bubble tiltmeter installed at 12m with the aim of investigating mechanisms by which meteorology including groundwater level affects tilt most similar measurements of tilt e g in north america new zealand and germany using various techniques at different depths in different geological conditions indicate meteorological perturbations of the tilt signal and it is suggested that continuous monitoring of water table level will enable these perturbations to be better understood

measurement and interpretation of tidal tilts in a small array strain induced tilts caused by variations in material properties can produce large perturbations in the tilt field near a material discontinuity this is evidenced in data from a closely spaced array of borehole tiltmeters that has been operating at piiion flat geophysical observatory in southern california since 1987 the array is composed of three borehole tiltmeters located at depths of 24 36 and 120 m the tiltmeters have a sensitivity of a few nanoradians tidal measurements show differences between the boreholes of up to 50 the largest percent difference occurs in the semidiurnal band where the tilt field measured in the 36 m borehole differs by 10 nrad at the m2 frequency this difference has been modeled as a strain induced tilt caused by the weathering layer

point stability at shallow depths experience from tilt measurements in the lower rhine embayment germany and implications for high resolution gps and gravity recordings summary from 1996 to 1999 we have studied ground tilts at depths of between 2 m and 5 m at three sites in the lower rhine embayment lre western germany the lre is a tectonically active extensional sedimentary basin roughly 50 kmr100 km the purpose of the tilt measurements was a to provide insight into the magnitude nature and variability of background tilts and b to assess possible limitations of high resolution gps campaigns and microgravity surveys due to natural ground deformation the tilt readings sensed by biaxial borehole tiltmeters of baselength 0 85 m cover a frequency range from 10 x8 hz to 10 x2 hz periods from minutes to years assuming that the tilt signals represent ground displacements on a scale typically not larger than several times the tiltmeters baselength and that tilt signals at shallow depth could in a simple geometric way be related to changes in surface elevation and gravity we try to estimate the magnitude level of point movements and corresponding bouguer gravity effects that is generally not surpassed the largest tilt signals observed were some t50 mrad yr x1 i f they were observable over a ground section of extension e g 10 m the converted rates may correspond to about t0 5 mm per 10 m yr x1 in vertical ground displacement and t0 1 mgal yr x1 in bouguer gravity effect respectively large signals are mostly related to seasonal effects probably linked to thermomechanical strain other causes of ground deformation identified include seepage effects after rainfalls order of t10 mrad and diurnal strains due to thermal heating and or fluctuations in the water consumption of nearby trees order of t1 mrad episodic step like tilt anomalies with amplitudes up to 22 mrad at one of the observation sites might reflect creep events associated to a nearby active fault except for short term ground deformation caused by the passage of seismic waves from distant earthquakes amplitudes of non identified tilt signals in the studied frequency range seem not to exceed t2 mrad as the larger tilt signals are close to the precision achieved with modern gps systems and superconducting gravimeters when converted into height and gravity changes further enhancement in resolution of these techniques may require simultaneous recording of local ground deformation at the observation sites

hydromechanical interactions in a fractured carbonate reservoir inferred from hydraulic and mechanical measurements hydromechanical coupled processes in a shallow fractured carbonate reservoir rock were investigated through field experiments coupled with analytical and numerical analyses the experiments consist of hydraulic loading unloading of a water reservoir in which fluid flow occurs mainly inside a heterogeneous fracture network made up of vertical faults and bedding planes hydromechanical response of the reservoir was measured using six pressure normal displacement sensors located on discontinuities and two surface tiltmeters a dual hydraulic behavior was characterized for low permeability bedding planes well connected to highpermeability faults displacement responses show high variability nonlinear changes sometimes with high frequency oscillations and a large scattering of magnitudes initial normal stiffnesses and effective normal stresses along fault planes were estimated in the field by interpreting pressure normal displacement relations with a nonlinear function between effective normal stress and normal displacement two dimensional discontinuum modeling with transient fluid flow was performed to fit measurements during hydraulic loading tests results show that the hydromechanical behavior of the reservoir is restored if a high stiffness contrast is allocated between low and high permeability discontinuities thus a dual permeability network of discontinuities will likely also be a contrasting stiffness network in which the deformation of major flow conducting discontinuities is significantly influenced by the stiffness of the surrounding less permeable discontinuities

water table effects on the measurement of earth strain abstract forced changes in the water head within a granite penetrating borehole were found to induce anomalously large free surface strains and tilts in the vicinity of the hole this deformation is shown to be due to fluid pressure induced changes in the aperture of a compliant hydraulically conductive fracture at a depth of 100 m and a quantitative analysis of the deformation data is performed to recover fracture characteristics the importance of the effect for secular earth strain measurements is discussed in the light of the ubiquitous nature of both water table fluctuations and fractures in the shallow crust

wind driven lateral circulation in a stratified estuary and its effects on the along channel flow 1 in the stratified rotating estuary of chesapeake bay the ekman transport drives a counterclockwise lateral circulation under down estuary winds and a clockwise lateral circulation under up estuary winds looking into estuary the clockwise circulation is about twice as strong as the counterclockwise circulation analysis of the streamwise vorticity equation reveals a balance among three terms titling of the planetary vorticity by vertical shear in the along channel current baroclinic forcing due to sloping isopycnals at cross channel sections and turbulent diffusion the baroclinic forcing is highly asymmetric between the down and up estuary winds while the counter clockwise lateral circulation tilts isopycnals vertically and creates lateral barolinic pressure gradient to oppose the ekman transport under the down estuary wind the clockwise circulation initially flattens the isopycnals and the baroclinic forcing reinforces the ekman transport under the up estuary wind the coriolis acceleration associated with the lateral flows is of the first order importance in the along channel momentum balance it has a sign opposite to the stress divergence in the surface layer and the pressure gradient in the bottom layer thereby reducing the shear in the along channel current compared with the non rotating system the shear reduction is about 30 40 two summary diagrams are constructed to show how the averaged streamwise vorticity and along channel current shear vary with the wedderburn w and kelvin ke numbers

estimating the hydrologic induced signal in geodetic measurements with predictive filtering methods the high precision achieved with continuous geodetic instruments makes it necessary to take ambient factors into account among these one of the most disturbing is the hydrologic agent after giving a characterization of the induced signals in the specific case of subsurface tilt and extensometric measurements the techniques of predictive filtering are shown to solve the problem of modeling the induced signals the results obtained here may be applied also to other continuous geodetic and gravity measurements

collection and three dimensional modeling of gps and tilt data at merapi volcano java we study here the deformations associated with the november 1996 to march 1997 eruption period at mount merapi central java one of the most active volcanoes in indonesia this activity period includes a vertical explosion on january 17 and an increase of the lava dome volume by about 3 106 m3 two global positioning system gps campaigns have been carried out on a six benchmark network at the beginning and at the end of the period relative displacements with respect to the reference point show an average subsidence of 6 5 cm a multicomponent tilt station installed on the southeast flank 3 km from the summit recorded a tilt of 11 1 0 7 rad in the tangential direction and 0 9 0 4 rad in the radial direction these data are interpreted using a three dimensional 3 d elastic model based on the mixed boundary element method and a near neighbor monte carlo inversion interpretation of tilt data requires an accurate mesh for discretizing the 3 d topography the final result supports a horizontal elliptic magma source located 8 5 0 4 km below the summit and 2 0 4 km to the east of it in particular the data cannot be consistent with the location of a magma chamber determined from seismic activity analysis i e 2 km below the summit the computed depth depends strongly on the source shape and cannot be constrained properly because of the small amount of data the computed deflation of 11 2 106 m3 is about 3 times larger than the observed increase in the lava dome volume this difference is attributed to rock avalanches and pyroclastic flows on the flanks of the volcano

the oceanic response of the turkish straits system to an extreme drop in atmospheric pressure moorings across all four entry exit sections of the dardanelles strait and the bosphorus strait simultaneously measured the response of the turkish straits system to the passage of a severe cyclonic storm that included an atmospheric pressure drop of more than 30 mbar in less than 48 h the bottom pressure response at the aegean sea side of the dardanelles strait was consistent with an inverted barometer response but the response at the other sections did not follow an inverted barometer leading to a large bottom pressure gradient through the turkish straits system upper layer flow toward the aegean sea was reversed by the storm and flow toward the black sea was greatly enhanced bottom pressure across the sea of marmara peaked 6 h after the passage of the storm s minimum pressure the response on the dardanelles side was a combination of sea elevation and pycnocline depth rise and the response on the bosphorus side was an even greater sea elevation rise and a drop in pycnocline depth the peak in bottom pressure in the sea of marmara was followed by another reverse in the flow through the dardanelles strait as flow was then directed away from the sea of marmara in both straits a simple conceptual model without wind is able to explain fluctuations in bottom pressure in the sea of marmara to a 0 89 0 96 level of correlation this stresses the importance of atmospheric pressure dynamics in driving the mass flux of the turkish strait system for extreme storms

turbulent mixing induced by nonlinear internal waves in mono lake california describing the spatial and temporal occurrence of turbulent mixing and the mechanisms of turbulence production are fundamental problems in physical limnology and oceanography here we present results from mono lake california that illustrate pronounced steepening of the pycnocline upon cessation of strong wind forcing and the enhanced turbulence resulting from this nonlinearity three events occurred with wind speed of 10 m s21 upwind the upper pycnocline upwelled but on relaxation of the wind it downwelled 6 10 m and compressed the similarity of wave amplitude during compression to mixed layer depth and lake numbers 4 were indicative of significant nonlinearity energy in the internal wave field increased by two orders of magnitude but 50 of the energy was lost within 24 h the largest energy losses occurred at low frequencies rather than via an energy flux from low to moderate and high frequencies eddy diffusivities computed over 6 d intervals using the heat budget method averaged 1026 m2 s21 in the energized pycnocline but were five to 10 times higher during the initial upwelling and downwelling periods microstructure casts taken 1 2 d after the first event revealed that the percentage of the pycnocline that was turbulent varied with bottom slope being 80 turbulent where bottom slopes were up to 10 6 0 where bottom slopes were 3 and less than 7 where bottom slopes were 0 1 the threshold for turbulent transport was exceeded only 10 of the time and only where bottom slopes were highest

monitoring deformation from hydrologic processes in a karst aquifer using long baseline tiltmeters 1 the aim of this study is to bring new information on water storage dynamics in karst systems from tiltmeter measurements newly developed long base hydrostatic tiltmeters are installed at two sites on the larzac plateau france in a karst aquifer of 100 km2 recharge area each site is located within a karst cave where two tilt directions are monitored significant reversible tilt deformation reaching amplitudes of 10 6 to 10 5 rad was observed at both sites following heavy precipitation elastic parameters were determined with an experiment in which a tiltmeter site was loaded by up to 25 t of weight at strategic locations at the ground surface mechanisms responsible for the observed tilt were then examined by means of finite element modeling deformation induced by water pressure changes in fractures is our preferred interpretation as the most plausible mechanism within this scope we used the tiltmeter responses to extract time constants using lumped parameter modeling time constants are interpreted to be associated with the filling and emptying of fractures nearby the tiltmeters these instruments therefore appear as useful tools to study the local dynamics of water infiltration in karst systems

short time scale correlation between slow slip and tremor in cascadia 1 we use borehole strain and seismic data to show that slow slip and tremor in central cascadia are correlated on a range of time scales shorter than 1 day the recorded strain rate is our proxy for the slow slip moment rate and the seismic amplitude is our proxy for the tremor amplitude we find that on average the strain rate is higher when the seismic amplitude is larger this correlation persists on time scales between 15 min and 16 h and it can be seen in each of the five slow slip events between 2007 and 2011 our results imply that the slow slip moment rate varies by a large amount even at these short time scales for instance we observe a factor of 2 variation on time scales shorter than 4 h this apparently aperiodic variation is larger than the previously observed variation in moment rate resulting from tidal forcing it is a lower bound on the actual moment rate variation as we detect only changes in slow slip that are correlated with tremor amplitude

displacement of surface monuments horizontal motion measurements of tectonic deformation depend on both accurate instrumentation and adequate coupling of the apparatus to the earth s crust existing techniques capable of resolving the signals of interest strain rates of 10 n yr are mainly observatory based the limitation in the baselength of these instruments 1 km results in a requirement that the reference monuments be exceptionally stable 10 tzm yr however records from pition flat observatory california show that the actual horizontal displacements for massive near surface monuments eraplaced in competent weathered granite are of the order of 50 tzm yr the low noise level of the strain measurements at this site indicates that this magnitude of monument displacement is abnormally small until high accuracy geodetic techniques are developed sophisticated monuments or monument monitoring devices will be necessary to record faithfully continuous crustal deformation

topographically controlled circulation and mixing in a lake it is well known that the wind driven circulation in a wide lake may be controlled by its topography wind stress acting on the smaller mass of the water column in the shallows results in downwind flow there and return flow in the deeper water in lakes with large areas of shallow water this circulation may cause rapid mixing in weakly stratified conditions in more strongly stratified conditions topographically induced horizontal wind driven circulation may influence the vertical stratification of the lake lough mask is about 10 km long and has a maximum width of about 8 km the lake may be divided into shallow eastern and deeper western portions with mean depths of 10 and 35 m respectively in late autumn water at depth in the deep part of the lake moves upwind at speeds of up to 50 cm s 1 in response to axial winds of up to 15 m s 1 at the same location a weaker upwind flow is observed in the near surface water this return flow is topographically driven temperature differences between near surface and near bottom meters were small 20 m surface mixed layer and a cooler layer at depth whose temperature fluctuates in response to wind stress along the axis of the lake modelling results supported by drogue measurements indicate that the return flow associated with axial winds in these summer conditions is confined to the surface mixed layer if this layer is thin shear between the surface layer and the underlying water can be sufficient to cause mixing and a thickening of the surface layer until the richardson number is 1 thus the vertical temperature structure of the deep part of the lake can be influenced by flows driven by the lake topography in the shallow part of the lake there is evidence of thermally driven motion in periods of calm weather in summer

continuous measurements of crustal deformation for the 1992 landers earthquake sequence abstract we describe and attempt to interpret continuous measurements of strains and tilts made at pinon flat observatory pfo before during and after the landers and joshua tree earthquake sequences these data show substantial transient deformation following the landers mainshock with a total amplitude of several percent of the co seismic deformation and a decay time of at least several days comparing data from the many types of instruments at pfo allows us to infer possible sources for this deformation the immediate postseismic transient was nearly the same size on three long base strainmeters suggesting either broadscale deformation or local motion near one part of the observatory the latter can largely be ruled out by the similarity of many other measurements in the area covered by these strainmeters and the observations by others of significant postseismic displacements nearer the source possible mechanisms for broad scale deformation include postseismic fault slip time dependent creep in near surface rocks and elastic or thermal responses to water table changes the first two agree best with the observations from pfo but if postseismic fault slip is the source it must have been distributed differently than the co seismic slip and may have included faults other than those that ruptured seismically if one of the other mechanisms is the main source the pfo data imply that the postseismic slip must have been very much smaller than the seismic slip perhaps 2 or less no significant preseismic deformation was observed at a level of 2 10 3 of the co seismic deformation for the days to minutes before the earthquake

observations of the lateral structure of wind driven flow in a coastal plain estuary abstract wind stress is one of the main drivers of estuarine circulation the lateral structure of wind induced flows in estuaries has been described mainly with analytical and numerical models the aim of this study is to investigate with observations the lateral structure of wind induced flow in a coastal plain estuary the james river virginia such structure was explored with the first empirical orthogonal function eof1 mode derived from month long moored adcps deployed at two cross sections in the estuary mode 1 explained 53 of the variance and was attributed to wind forcing its lateral structure eigenvectors consisted of upwind flow centered in the channel at middle depth downwind flow over the shoals and a vertically sheared bidirectional flow over the channel slope wavelet coherence analysis showed that along estuary wind was highly coherent with mode 1 coherence squared 0 9 especially at the period band between 4 and 6 days the along estuary wind stress and the temporal variation of mode 1 showed an anti phase coherence with the wind stress leading mode 1 persistently in addition an analytical solution showed a lateral structure similar to the eigenvectors obtained with eof1 the conclusion is that the lateral structure described by eof1 was induced by wind stress and was consistent with analytical and numerical model results these results are among the handful available that confirm the theoretical structure of wind driven flows over laterally varying bathymetry

effects of winds on stratification and circulation in a partially mixed estuary 1 numerical experiments are conducted to investigate how axial winds affect stratification and circulation in the partially mixed estuary of chesapeake bay in the absence of rotational effects stratification in the estuary decreases following both down estuary and up estuary winds but stratification experiences larger reduction and takes longer to recover under up estuary winds in the presence of rotational effects wind driven lateral circulations cause the lateral straining of density field and weaken the shear in the along channel flows under the down estuary winds a counterclockwise lateral circulation steepens isopycnals in the cross channel sections while the coriolis force acting on it decelerates the downwind current in the surface layer and the upwind directed current in the bottom layer under the up estuary winds a clockwise lateral circulation flattens isopycnals in the cross channel sections and reduces the shear between the surface and bottom currents hence in the presence of rotational effects the lateral straining offsets the effects of longitudinal straining such that the asymmetry in stratification reduction is significantly reduced between the down estuary and up estuary winds regime diagrams based on wedderburn w and kelvin ke numbers are constructed to summarize the net effects of winds on estuarine stratification during both wind perturbation and postwind adjustment periods

tectonic vs shallow origin of geodetically inferred ground movements an ne ardenne belgium case in order to get a better insight into the temporal pattern of height change variations in a moderately seismic intraplate area a 1 km long section has been weekly leveled from april 21 1997 to january 12 1998 in ne ardenne belgium as this section is located very close to a small reservoir of 25u10 6 m 3 it also allowed the influence of lake level variations on the nearby ground motion to be studied the measured height difference variations show a maximum amplitude of 3 45 mm with weekly values not exceeding 1 mm a two dimensional 2d finite element modeling confirms that waterload variations in the lake are the primary cause of movement of the section inducing maximum ground subsidence of about 2 cm and seasonal tilting of 3 4 wrads within a range of 2 3 km we also show that a fault passively alters the spatial distribution of the waterload dependent movements the removal of this component from the observed ground motion leaves oscillating residual displacements characterized by an amplitude of 1 1 5 mm and a period of about 2 months we demonstrate that these displacements are independent of rainfall and probably of groundwater fluctuation too although most of the residual motions take place on the fault straddled by the leveling section no credible mechanism can be found to ascribe these motions to a tectonic process fl 2000 elsevier science b v all rights reserved

differential cooling drives large scale convective circulation in lake tanganyika field data scaling analysis and three dimensional numerical experiments demonstrate that the dominant large scale circulation pattern during the southeast trade winds in lake tanganyika east africa is a downwind flow in the metalimnion with a returning southward upwind flow in the upper region of the epilimnion this is in the opposite direction to all prior literature available on the lake which has assumed that the southeast trade winds must drive a northward surface flow due to momentum induced by the wind the gradient in wind speed and humidity along the length of the lake and the resulting gradient in heat exchange with the atmosphere result in warm water accumulating at the northern end of the lake the north basin of lake tanganyika thus acts as a heat sink while the south basin is a net source of heat to the atmosphere the resulting variation in buoyancy flux is strong enough to drive a convective flow in the upper layer in the opposite direction to the wind a large scale convective circulation results in an annual exchange of 6 2 1012 m3 of water and an annual net transport of heat averaging 0 2 terawatt from the northern to the southern region of the lake currents in the upper 100 m layer with a mean flow of 0 2 sverdrup and flow speed of 0 08 m s 1 can be described by the superposition of a parallel convective flow with the internal seiche motion

internal hydraulic jumps in a long narrow lake high resolution three dimensional numerical modeling and field observations were used to describe the nonlinear response of cayuga lake to surface wind forcing the degeneration of the basin scale internal wave field was characterized according to the composite froude number g2 wedderburn number wn and lake number ln which are measures of hydraulic control and bulk and integral wind disturbance force to the baroclinic restoring force respectively the typical cayuga lake response was a nonlinear surge when 1 1 in a lake the occurrence of the hydraulic jump was correctly predicted using scaling parameters it was also shown that topographically induced internal hydraulic jumps form when the nonlinear surges interact with a sill contraction topographic feature in contrast to published literature the observed high frequency nonlinear internal waves were preferentially associated with internal jumps as opposed to steepened internal surges computed vertical diffusivities showed mixing was enhanced by two orders of magnitude within both the surges and hydraulic jumps as they propagated through the basin and interacted with topography our results can be generalized to other lakes and fjords with similar long narrow geometry and topographically separate side basins

differential mixing in a stratified fluid we present an experimental and theoretical study of the effects of localized mixing on a stratified fluid contained in a reservoir in the experiments mixing is accomplished by means of a vertically oscillating horizontal grid located near the water surface at one end of the reservoir once the grid is set in motion a mixed layer forms immediately beneath it as this layer deepens a horizontal pressure gradient builds up which drives an outflow of mixed fluid into the unmixed interior of the reservoir this outflow slows and eventually brings to a halt mixed layer deepening under the grid at this equilibrium depth the vertical velocity of the entrainment interface induced by the outflow exactly equals the velocity at which the entrainment interface would move downwards because of mixing this equilibrium state persists until the outflow intrusion is blocked by the far wall of the reservoir at which time deepening resumes under the grid asymptotically the fluid reaches a state in which mixed layer deepening is independent of position

tilt and strain deformation induced by hydrologically active natural fractures application to the tiltmeters installed in sainte croix aux mines observatory france we investigate the deformation induced by water pressure variations in hydrologically active natural fractures and recorded by tiltmeters and strainmeters the deformation associated with a single fracture is derived using finite element modelling fem a range in fracture geometries is explored first to highlight the sensitivity of each geometrical parameter to the deformation and secondly to allow transfer to observation sites water level variations in the fracture are then derived from a hydrological model driven by observed rainfall and calibrated on fracture water flow measurements the modelling results are explicitly applied to constrain the local hydrological contribution to observations with the 100 m long hydrostatic tiltmeter installed at sainte croix aux mines france our study shows that well founded physical modelling of local hydrological effect allows a substantial correction of records in observatories

energy partitioning and horizontal dispersion in a stratified rotating lake abstract the response of a stratified rotating basin to the release of a linearly tilted interface is derived this case is compared with a uniformly forced basin in the two limits when the duration of the forcing is much greater than the period of the dominant internal waves and when it is much smaller energy partitioning is studied as a function of the burger number s relative importance of stratification versus rotation showing the dominance of a geostrophic component over the wave field for low s trajectories are integrated numerically revealing the stokes drift of the waves to be always cyclonic transport properties are classified in terms of s and the wedderburn number w relative importance of the disturbance versus stratification the geostrophic flow is the main source of advection but only the waves allow particles to break the barrier to transport between the two geostrophic gyres ultimately leading to stretching and folding for low values of w advection can become chaotic conserva

katabatic wind driven exchange in fjords the general issue of katabatic wind driven exchange in fjords is considered using an idealized numerical model theory and observations two regimes are identified for fjords narrower than a viscous boundary layer width the exchange is limited by a balance between wind and friction in lateral boundary layers for the nonlinear viscous parameterization used here this boundary layer thickness depends on the properties of the fjord such as stratification and length as well as on the wind stress and numerical parameters such as grid spacing and an empirical constant for wider fjords typical of east greenland the balance is primarily between wind the along fjord pressure gradient and acceleration in general agreement with previous two layer nonrotating theories it is expected that o 10 of the surface layer will be flushed out of the fjord by a single wind event application of the idealized model to a typical katabatic wind event produces outflowing velocities that are in general agreement with observations in sermilik fjord the presence of a sill has only a minor influence on the exchange until the sill penetrates over most of the lower layer thickness in which cases the exchange is reduced it is concluded that the multiple katabatic wind events per winter that are experienced by the fjords along east greenland represent an important mechanism of exchange between the fjord and shelf with implications for the renewal of warm salty waters at depth and for the export of glacial freshwater in the upper layer

measurements and interpretations of tilt strain gauges in seismically active areas abstract an overview of different aspects of deformation measurements is given an introduction to the general theory of point crustal deformations with an application to the stress strain relations at the earth surface is made the instrumentation used in crustal deformation measurements is briefly explained emphasizing different constructions of tilt and strainmeters the problems connected with the housing of the instruments i e the cavity and topography effects and with the ambient noise factors as the hydrological and pressure effects are discussed the last part of the paper is concerned with the relation between deformation measurements and seismic events both from a theoretical and observational standpoint a number of examples are shown that report on pre co and post seismic and the secular term deformation in different areas of the world

comparing tiltmeters for crustal deformation measurement a preliminary report a collection of high precision tiltmeters is being operated at pinon flat observatory southern california both to compare instruments and to measure tectonic deformation we report on 1 2 years of data from four of these two michelson gale long fluid tiltmeters one long center pressure tiltmeter and a shallow borehole tiltmeter the three long base instruments are all located on the same baseline with a precise leveling line running between their end monuments at nontidal frequencies only the two michelson gale instruments show some coherence 3 for periods of 2 to 4 days while the center pressure instrument is correlated with air temperature at periods from a few days to a few weeks the most stable tilt record shows a secular rate of 0 28 rad a which may be real over much longer times leveling to specially stabilized benchmarks should confirm this comparing instruments has identified more and less successful measurement techniques it appears that low noise data will most probably be produced only by relatively complex and expensive instruments though even for these the operating costs over any reasonable lifetime will exceed the capital cost even the best existing sensors must be improved to measure continuous tectonic motions

numerical simulation of coastal upwelling and inerfacial instability of a rotaion and stratified fluid the evolution of the coastal upwelling and interfacial instability of a stratified and rotating fluid is studied numerically by using large eddy simulation upwelling is generated near the sidewall of a rotating annulus by the shear at the top the fluid initially consists of a stably stratified two layer structure with a narrow interface separating the two layers the large scale motion of the flow is simulated by solving the time dependent non hydrostatic incompressible navier stokes and scalar transport equations while the small scale motion is represented by a dynamic subgrid scale model the upwelling process contains both stable and unstable stratification the vertical structure of upwelling consists of a persistent primary front a trailing mixing zone on the shore side of the front and a temporary secondary front which leads a top inversion layer the longshore velocity profile has two maxima which occur at the edge of the sidewall boundary layer and at the density front the upwelled density front is unstable to azimuthal perturbations and baroclinic waves develop and grow to large amplitude pairs of cyclonic and anticyclonic waves appear at the front which form jet streams the secondary front is unstable to azimuthal perturbations its instability and the associated drop of the top inversion layer take the form of radial bands which subsequently break up into isolated patches and eventually sink the computed values of various upwelling time and length scales are compared to and are in good agreement with past experimental data

tilt measurements in western canada pairs of short baselength mercury level tiltmeters mounted on shallow piers coupled to sedimentary rocks have been used to monitor ground tilting at three inland locations in western canada noise levels have been estimated over large nyquist intervals to evaluate site conditions and for comparison with results observed in crystalline rocks at other locations the results show that tilt noise patterns are similar for different locations and that noise levels are higher for unconsolidated sediments tidal estimates for the principal lunar semidiurnal constituentm2 were obtained from the least noisy sections of the tilt series uncertainties in the estimated amplitudes for the record lengths considered range from 4 to 20 depending on location and azimuth comparison of the observedm2 tide with those predicted for an elastic earth loaded by two different ocean configurations schwiderski or parke shows better agreement with the schwiderski marine tidal model differences between observaton and theory suggest a strain induced perturbation source

chronology and evolution of caldera forming and post caldera magma systems at okataina volcano new zealand from zircon u th model age spectra u th disequilibrium model age data are presented for zircons from four young eruptive units from okataina volcano new zealand these data highlight contrasts in the time scales over which eruptible silicic magma bodies are generated and accumulated below a highly active rhyolite volcano prior to and following the 61 ka caldera forming rotoiti eruption 80 120 km 3 magma the rotoiti event was followed by 12 explosive eruptions of the mangaone subgroup between 45 and 30 ka a change in eruptive styles between 30 and 25 ka brackets the major oruanui eruption of taupo volcano 80 km away subsequently eight rhyolitic lava dominated and two basaltic explosive eruptions occurred between 25 ka and 1886 ce we present 238 u 230 th zircon model age data determined by secondary ion mass spectrometry sims and thermal ionization mass spectrometry tims from the rotoiti ngamotu unit b 45 ka mangaone unit i 33 ka and rotorua 15 4 ka eruptive units we couple these data with published and new compositional information to trace magma crystallization and storage patterns population density curves of sims model ages from zircons in the two pumice types biotite free and biotite bearing from the rotoiti eruption differ zircons from the former yield a model age peak coincident with eruption age whereas zircons from the latter show a peak at 70 90 ka and little variation in tims model age values from different crystal size fractions concentration weighted means of model ages from the two pumices however are the same within 1 sd error and their sr isotopic values overlap at 2 sd precision suggesting that they are genetically linked model age spectra for the ngamotu mangaone and rotorua pumices are complex indicating recycling of crystals from multiple older populations that largely pre date the 61 ka caldera forming eruption superimposed on the older age spectra are variably developed younger pre eruptive suites of ages reflecting varying amounts of crystallization prior to each eruption a lack of commonality in these younger peaks in the post caldera eruptive rocks along with compositional and isotopic differences between and sometimes within the eruptive units collectively precludes their origin from a single melt bearing mush system okataina contrasts with taupo where comparable age eruption deposits have simpler age spectra consistent with larger scale crystallization cycles and thermal events in the magma chambers there when compared with other caldera related silicic systems for which suitable data are available okataina differs in lacking a simple pre eruptive history prior to its caldera forming event and having a complex non coherent magmatic history of post caldera eruptions

subtidal hydrodynamics in a tropical lagoon a dimensionless numbers approach abstract observations in a tropical lagoon of the yucatan peninsula motivated a non dimensional number analysis to examine the relative influence of tidal stress density gradients and wind stress on subtidal hydrodynamics a two month observation period in chelem lagoon covered the transition from the dry to the wet season chelem lagoon is influenced by groundwater inputs and exhibits a main sub basin central sub basin a west sub basin and an east sub basin subtidal hydrodynamics were associated with horizontal density gradients that were modified seasonally by evaporation precipitation and groundwater discharge a tidal froude number fr 0 a wedderburn number w and a stress ratio s 0 were used to diagnose the relative importance of dominant subtidal driving forces the froude number fr 0 compares tidal forcing and baroclinic forcing through the ratio of tidal stress to longitudinal baroclinic pressure gradient the wedderburn number w relates wind stress to baroclinicity the stress ratio s 0 sizes tidal stress and wind stress s 0 is a new diagnostic tool for systems influenced by tides and winds and represents the main contribution of this research results show that spring tide subtidal flows in the tropical lagoon had log fr 0 0 and log s 0 0 i e driven mainly by tidal stresses advective accelerations neap tides showed log fr 0 0 and log s 0 0 i e flows driven by baroclinicity especially at the lagoon heads of the east and west sub basins however when the wind stress intensified over the lagoon the relative importance of baroclinicity decreased and the wind stress controlled the dynamics log w 0 each sub basin exhibited a different subtidal response according to the dimensionless numbers the response depended on the fortnightly tidal cycle the location and magnitude of groundwater input and the direction and magnitude of the wind stress

new insights on fractures deformation from tiltmeter data measured inside the fontaine de vaucluse karst system tilt fluctuations can potentially reflect the response of hydrosystems to important rainfall in this context long baseline tiltmeters have been installed in an underground tunnel penetrating the fontaine de vaucluse karst to study the medium deformation related to solicitations exerted by water infiltrating the hydrosystem the instruments monitor the tilt as well as its spatial variation northward tilts reaching a 1 rad amplitude are observed consecutively to rainfalls the tilt amplitude is highly correlated with the fontaine de vaucluse outlet flow fluctuations the measured tilt signal is also relatively homogeneous over a 150 m length different types of structure likely to produce such observations are tested in order to identify their location with respect to the tiltmeters their dimension as well as the amount of water level variation in the structure following rainfalls the infiltration of water modifies the pore pressure inducing a medium deformation the hypothesis of an homogeneous surface loading on the vaucluse plateau is first refuted since the related tilt is much lower than the one measured the water supplied by rainfalls has to accumulate in discontinuities in order to generate a higher tilt so the deformation related to a pressure exerted on a fracture filled by water is assessed a first study reveals the interest of the tilt homogeneity information that constrains strongly the fracture properties thus the fracture must be located at a distance more than a few hundreds metres from the tiltmeters in order to produce a tilt homogeneous in space if the fracture is initially dry it must also be filled on a height higher than 150 m consecutive to a rainfall in order to generate a tilt amplitude in the same magnitude as the one measured then we explore the influence of water level variations on the tilt produced by a fracture located at the interface between the saturated and unsaturated zones which are thereby permanently flooded since several parameters of that model satisfactorily explain the field observations we discuss how simultaneous geodetical observations could provide complementary information that would further constrain the geometry of the structure at the origin of the medium deformation

observed flow variability along the thalweg and on the coastal slopes of the gulf of finland baltic sea abstract bottom mounted adcp measurements from 10 installations collected between 2009 and 2014 and each lasting several months are analysed in order to distinguish between different flow regimes and to detect variability a along the thalweg of the elongated basin with different regimes in summer and in winter and b on the coastal slopes in the deep thalweg area the mean flow speed amounts to 6 13 cm s 1 whereas the maximum speeds appear in winter near the bottom of the basin and in summer within the halocline around 70 m depth the mean zonal flow component reveals a nearly depth uniform inflow during winter and a layered inflow outflow during summer in years where up estuary w to sw winds are stronger during the summer inflow dominates in upper layers and anti estuarine outflow dominates in deeper layers this causes the export of a salt wedge and the weakening of haline stratification infra low frequency zonal currents i e excluding topographic waves etc with periods of less than 10 days have a structure which is uniform with depth for 53 of the time in winter in summer a layered structure is present 65 of the time however during both periods the reversed estuarine flow inflow in upper layers and outflow in the bottom layer appears on average for 30 of the time the deep flow zonal component is well correlated with westward winds during summer r 0 84 and south westward winds during winter r 0 77 on the coastal slopes the speed of the currents are lower than in the thalweg region and they decay with depth in the vertical the flow exhibits a layered structure in both the winter and summer seasons

wind driven upwelling in opunohu bay moorea french polynesia abstract opunohu bay is a narrow straight 3 km long bay on the island of moorea french polynesia the bay is open to the ocean with a water depth of about 80 m at the mouth the sea floor slope reaches one third offshore field observations show that a wind blowing to offshore along the axis of the bay generates an outflow at the surface and an inflow below 20 m depth a localized upwelling results at the mouth of the bay which may also be detected in the phytoplankton population this situation is modelled numerically and the results suggest that the wind stress must be taken to be not only a function of the wind speed but also of the wind fetch

mechanisms of pore pressure stress coupling which can adversely affect stress measurements conducted in deep tunnels rock stress measurements performed in boreholes drilled from a tunnel at a depth of 800 m indicate that the minimum stress has been reduced from pre excavation levels by drawdown in pore pressure the disturbance to the ambient stresses extends well beyond two tunnel diameters a model is developed to explain the inferred strong coupling between the pore pressure and minimum stress in the rock mass around the tunnel the model includes the effects of poro elasticity of the intact rock and the stiffness of the fractures for the field situation under study where the fractures are unusually complaint both poro elasticity and fracture compliance could be important contributors to the coupling changes in pore pressure are shown to produce reductions in minimum stress that are at least 50 of the drop in pore pressure and probably higher in more general situations the poro elastic component is likely to be the more significant of the two mechanisms and alone accounts for a coupling factor of 50 in this context the importance of fractures in crystalline conditions probably lies more in their promotion of penetrative drainage than their contribution to coupling coefficient the results highlight the importance of establishing the extent and distribution of pore pressure drawdown about galleries from which stress measurements are to be conducted

on the structure of transient upwelling events abstract nearshore transcends following the development of transient coastal upwelling characteristically show intermediate density fluid occupying the immediate nearshore band large cross shore particle excursions during the development of upwelling may be inferred from be fore and after transects and the movement of surface layers seaward intermediate density fluid shoreward through a distance of the order of kilometers and the bottom layers also shoreward by a 1esser amount some inevitable vertical mixing together with the large cross shore displacements results in efficient cross shore mass exchange the main dynamical features of similar events may be investigated by means of three layer models linear theory is conveniently discussed first the conclusions of which are easily generalized to multilayer models finite amplitude i e full upwelling is then considered using a potential vorticity conserving impulsive model the results show that the wind peels off the surface layer over w

axial wind effects on stratification and longitudinal salt transport in an idealized partially mixed estuary abstract a 3d hydrodynamic model regional ocean model system roms is used to investigate how axial wind influences stratification and to explore the associated longitudinal salt transport in partially mixed estuaries the model is configured to represent a straight estuarine channel connecting to a shelf sea the results confirm that wind straining of the along channel salinity gradient exerts an important control on stratification two governing parameters are identified the wedderburn number w defined as the ratio of wind stress to axial baroclinic pressure gradient force and the ratio of an entrainment depth to water depth hs h here w controls the effectiveness of wind straining which promotes increases decreases in stratification during down estuary up estuary wind the ratio hs h determines the portion of the water column affected by direct wind mixing while stratification is always reduced by up estuary wind stratification shows an increase then decrease transition when down estuar

a comparison of tiltmeters at tidal frequencies different techniques for measuring crustal deformation are now being tested at pinon flat geophysical observatory in southern california as a part of this comparison we have analyzed five months of data from four different tiltmeters three borehole instruments two 4 5 m and one 26 m deep and a long base 535 m instrument at the surface for periods from 1 hour to 10 days the signals from the deep borehole and long base instruments show comparable noise levels the shallow instruments are much noisier tidal analyses give results for the different sensors which agree to within the errors which are several percent

dynamics of wind driven circulation in a shallow lagoon with strong horizontal density gradient 1 albemarle pamlico sound aps is a shallow lagoonal estuary with weak stratification but strong horizontal density gradient idealized and realistic model simulations are conducted to examine the dynamics of wind driven circulation in aps two dimensionless parameters the ekman ek and wedderburn w numbers are found to be two key parameters in controlling the flow pattern and dynamics circulation in albemarle sound and northern pamlico sound is primarily driven by wind forcing and shows laterally sheared flows withek approaching 1 and wexceeding 1 analysis of the along channel momentum equation shows a balance among the wind stress barotropic pressure gradient due to sea level setup and bottom friction while the vertical vorticity is primarily determined by the balance between the wind stress curl and bottom stress curl in contrast circulation in southern pamlico sound is driven by both wind and gravitational forces and shows vertically sheared two layer flows with lowek and waround 1 both baroclinic and barotropic pressure gradients act against the wind stress to drive the two layer flows a regime diagram in the parameter space ofek and w is used to summarize variability of circulation pattern on the seasonal time scale northern pamlico sound is characterized by high ek and high w values and laterally sheared currents southern pamlico sound is usually characterized by low ek and low w values and vertically sheared flows but featuring laterally sheared flows during the fall when ek averages to over 0 5

a parametric study of the generation and degeneration of wind forced long internal waves in narrow lakes the generation and energy downscaling of wind forced long internal waves in strongly stratified small to medium sized narrow lakes are studied a two layer nonlinear model with forcing and damping is employed even though the wave field is fundamentally bidirectional in nature a domain folding technique is employed to simulate the leading order internal wave field in terms of a weakly nonlinear weakly dispersive model equation of korteweg devries type parametric effects of wind forcing and environmental conditions including variable topography and variable basin width are examined energy downscaling from basin scale waves to shorter scales are quantified by means of a time evolution of the wave energy spectra it is demonstrated that an internal wave resonance is possible when repetitive wind forcing events arise with a frequency near the linear seiche frequency an attempt is made to apply the model to describe the shoaling of long waves on sloping endwall boundaries modelling of the energy loss and energy reflection during a shoaling event is calibrated against laboratory experiments

recent crustal movements of tectonic or human originborehole tilt measurements aperiodic crustal tilt in an aseismic area nine months of tilt measurements at tidal sensitivity with an askania tiltmeter at a depth of 12m show aperiodic tilts with time scales of two days and upwards statistically significant correlations are found with meteorological variables and in particular with variations in the local groundwater table typically a variation in the tilt of 1 microradian is associated with a variation in the groundwater table of about 1 m the seasonal variation over the last two years in groundwater has a range of 3 m about a mean level approximately 2 5 m below the ground surface these variations have been continuously measured by a neyrpic tide gauge in a 50 m uncased borehole in addition to this seasonal variation are episodic events some in excess of 1m associated with heavy rainfall 2 3 cm these events have a rapid onset lasting 1 day followed by a decay lasting 10 days or more tilt events associated with similar groundwater variation could in a seismic region be easily mistaken for precursory tilt and this work emphasises the necessity of taking a complete account of meteorology in seismic zones where strain and tilt measurements are in progress further work is in progress with the askania tiltmeter which is now installed in an adjacent borehole at a depth of 30 m and a hughes tm 3 bubble tiltmeter installed at 12m with the aim of investigating mechanisms by which meteorology including groundwater level affects tilt most similar measurements of tilt e g in north america new zealand and germany using various techniques at different depths in different geological conditions indicate meteorological perturbations of the tilt signal and it is suggested that continuous monitoring of water table level will enable these perturbations to be better understood

vertical movement and gravity change near the la grande 2 reservoir quebec leveling and precise gravity observations were made along a 50 km profile before and after the filling of the la grande 2 reservoir 53 7 n 77 w in 1979 anomalous relative vertical uplift of 4 cm and relative changes in gravity of 14 gal 140 nm s2 were observed along the profile the observed changes are anomalous with respect to theoretical results for loading of a layered elastic earth homogeneous isotropic porous elastic models with reasonable hydraulic properties are also unable to explain the observations in an effort to account for the discrepancies the accuracies of the leveling and the gravity data were investigated corrections were made to the leveling data for refraction errors rod calibrations magnetic effects and deflection of the vertical by the water mass although the corrections for systematic errors were significant the discrepancy with respect to homogeneous isotropic loading models remains the anomalous increase in gravity is thought to be the result of lateral transport of water in a high permeability formerly undersaturated zone hydraulically coupled to the reservoir the anomalous uplift is thought to be the result of elastic expansion of cracks and fractures of low aspect ratio in the high permeability zone or the result of an unexpectedly high rate of regional tilting in the lagrande 2 area

exchange between a freshwater embayment and a large lake through a long shallow channel we analyze the exchange between a weakly forced lacustrine embayment and a large lake through a long shallow channel exchange in the channel is the result of a multiple and subtle balance in which spatial thermal variations baroclinic forcing oscillations in the water level barotropic forcing bottom friction diffusion wind forcing and the effects of unsteadiness are all important temperature gradients across the channel result from differences in thermal inertia of the embayment and lake at seasonal time scales and differences in the wind driven internal dynamics of the lake and the embayment at diurnal to synoptic time scales these gradients are in general weak and barotropic forcing dominates the channel momentum balance however episodic upwelling in the lake can shift the balance in favor of baroclinic dominance a combination of scaling analysis of observational data and threedimensional simulations are used to demonstrate that bed stress vertical turbulent diffusion wind stress and unsteadiness effect exchange relative to the predictions of internal hydraulic theory the quasisteady inviscid theory that describes the motion resulting from a purely barotropic baroclinic force balance

undercurrent driven upwelling in the northwestern arafura sea a three dimensional process oriented model is applied to explore the circulation in the arafura sea during the southeasterly monsoon during this period widespread phytoplankton blooms develop in a large area 300 km 300 km in the northwestern arafura sea the model findings indicate that undercurrents are the principal source of nutrient rich banda sea slope water for the region it is demonstrated that these undercurrents operate to flush the northwestern arafura sea with banda sea slope water on a time scale of 1 3 months which is consistent with observational evidence the simulated undercurrents are the signature of the classical lee effect frequently observed in lakes that comes into play in the arafura sea given its bay like geometry shallow water depth 40 50 m and close vicinity to the equator it is also shown that density stratification and rotational effects have important influences on the pathway and intensity of the overturning circulation in the northwestern arafura sea which needs to be further explored in the future

slip rate and mode of the feldbiss normal fault roer valley graben after removal of groundwater effects abstract the feldbiss fault is the main active fault bounding to the southwest the roer valley graben of nw europe in order to investigate the reasons of the discrepancy between its short and long term slip rate estimates we have repeatedly surveyed a 2 3 km long line by levelling at sittard the netherlands from april 2001 to december 2004 simultaneously three superposed aquifers were monitored on both sides of the fault the across fault differential groundwater variations are shown to be responsible for a seasonal 0 87 mm m vertical motion of the fault mainly through the effect of pore pressure changes in confined aquifers after removal of this effect i get a residual trend of 0 60 0 11 mm yr for the relative motion of the hangingwall this trend was disturbed in the summer of 2002 by transient millimetre level up and down motions temporally associated with the small eschweiler earthquake that occurred on july 22 2002 on the feldbiss fault at a distance of 35 km from sittard i explain this as a creep event triggered by the passage of trapped seismic waves the subsisting discrepancy between the long term slip rate of 0 06 mm yr and short term rates of 1 5 mm yr from 1962 to 2001 and 0 6 mm yr from 2001 to 2004 is tentatively interpreted as resulting from the current occurrence of a decade long episode of aseismic slip involving a large part of the fault plane occasionally associated with minor seismicity this aseismic slip event could betray a thickening of the transitional region located below the upper crustal zone of stable sliding it causes a total fault slip of 5 10 cm in a few tens of years releasing smoothly all or a great part of the strain accumulated during the previous 1 2 ky of fault quiescence

mixed layer deepening in lakes after wind setup laboratory experiments on wind driven mixed layer deepening in a wind flume are described for the situation where the wind shear stress has become balanced by a streamwise pressure gradient so that the mean mixed layer velocity has vanished the results were obtained at two lengths of the flume and include visual observations entrainment rates density profiles velocity profiles and profiles of turbulence intensities an intermediate upwind wedge formed by accumulation of mixed water was observed in all experiments the entrainment law obtained agrees with kraus and turner s relationship and is almost independent of the length of the flume

generalizations of the wedderburn number parameterizing upwelling in stratified lakes the effect of lake geometry on wind induced upwelling in a two layer stratified lake with a variable bottom slope and generic planar shape is investigated 1 the traditional linearized classification parameter for upwelling the wedderburn number is extended to include finite amplitude effects in a rectangular basin this extension is important when the wedderburn number is 3 2 the wedderburn number is generalized to incorporate the influence of a bottom slope and a variable width basin for both the linear large wedderburn number and nonlinear small wedderburn number assumptions laboratory and numerical experiments of a two layer stratification were performed and used to validate these extensions 3 both extensions are combined to derive a methodology to estimate the interface displacement in real lakes where both geometry effects may act together and this methodology is used to discuss the response of the thermocline to the onset of wind in lake como and mundaring weir reservoir in most cases symmetry of the basin geometry along the fetch is the key characteristic that defines tilting of the interface for real lakes asymmetries in terms of bottom slopes induce shortening or stretching of the effective internal fetch while a larger excursion of the interface results in narrower upwind areas of the lake due to horizontal redistribution of displaced water volumes this paper gives the correct definition of the length scales to define the wedderburn number for any stratified basin

dynamic response of the fluid mud to a tropical storm fluidmud fm isauniquesedimentaryfeatureinhigh turbidityestuaries whereitcanmake a rapid contribution to morphodynamics insuf cient eld measurements and xed point monitoring lead to de cient understandings of the formation transport and breakdown of the fm under extreme weather conditions a eld survey was conducted in the changjiang estuary during the period of turbidity maximum just after typhoon haikui the measurements captured the formation of the fm beneath the suspended layers particularly around the lower reach of the north passage the thickness of the observed fm gradually decreased landward along the channel with the maximum value reaching 0 9 m the major features of the observed storm induced fm were simulated using the finite volume community ocean model the results indicated that the initial appearance of the fm was the result of a typhoon intensi ed salinity induced strati cation in the outlet region the subsequent landward propagation of the fm was driven by the combined effects of the fm induced mud surface pressure gradient force and saltwater intrusion near the bottom weak mixing during the subsequent neap tidal period sustained the fm as it rapidly extended into the middle region of the north passage this produced a large velocity shear at the interface of the fm and upper suspension layer increasing the entrainment from the fm to the upper suspensionlayer asaresultoftheincreasedtidalmixing thefmweakenedandthen nallybrokedownin the subsequent spring tidal period

field measurements of normal and shear fracture compliance abstract field estimates of the normal and shear compliance of water saturated fractures were obtained from a seismic experiment carried out on a wave cut platform of upper caithness flagstone on the north coast of scotland the rocks are cut by two orthogonal sets of vertical fractures vertical geophones were glued to the rock surface and seismic waves were generated by striking the surface with a sledge hammer first arrival traveltimes were obtained for source receiver distances up to 30 m differences of compressional velocity with direction across the platform were interpreted as resulting from the compliance of the fractures intersected by the transmitted waves the average normal compliance for fractures at this site is 4 0 10 12 1 0 10 12 m pa there is much less certainty about the precise value of shear compliance however the normal shear compliance ratio is determined to be 0 1

wind forced motions in stratified lakes and their effect on mixed layer shear the solution for the response of a rectangular n layered stratified lake to an arbitrarily varying in time wind stress is presented the case n 3 is considered in detail for a three layered lake the response is made up of the individual responses of one external and two internal modes when the upper layer is shallow relative to the other two layers the mixed layer shear is due almost entirely to the slower second mode response moreover the upper interface can tilt quite severely while the lower interface remains nearly flat calculations based on the three layer model are compared with measurements made in wellington reservoir western australia

response of a large stratified estuary to wind events observations simulations and theory for long island sound abstractthe response to wind events in the long island sound lis a large macrotidal estuary influenced by rotation and stratification is studied using long term ferry based current observations near the mouth unstratified and stratified numerical simulations forced with along estuary winds and analytic solutions based on linear barotropic theory the observed wind event velocity anomalies for down estuary winds have surface intensified downwind flows flanking a deeper central upwind flow response to up estuary wind events has a weaker magnitude and a broader and thicker downwind flow the downwind and upwind flows are more laterally aligned than vertically layered as determined by a newly defined dimensionless lateral alignment index simulation results and analytic solutions share the gross spatial patterns of the observed response though statistical measures indicate weak agreement along estuary variations in the simulation results and analytic solutions follow similar trends and are strongly

contemporary plate motion and crustal deformation the measurement of relative plate velocities during the past few years is a signal accomplishment in earth science leading to refinement of the precepts of steady motion of plate interiors and cyclic deformation along plate margins regrettably deformation premonitory to an earthquake has yet to be detected with confidence delineation of the spatial and temporal buildup of strain between earthquakes however has put limits on models of the earthquake cycle a diverse set of fault structures and crustal rheologic conditions can explain the pattern of surface strain accumulation and release along strike slip faults in contrast the geometry of thrusts and normal faults revealed by earthquake deformation has been found to differ markedly from expectations geodetic observations have proved vital to monitor the ascent of magma through the earth s crust and to predict volcanic eruptions at the earth s surface episodic vertical and horizontal deformation in southern california remains a subject of dispute if anything it is less certain than it once seemed

strainmeters and tiltmeters despite steady effort over the last century continuously recording tiltmeters and strainmeters have not yet been successful except for earth tide measurements this article reviews the techniques and instrument designs that have been developed in this field the continuous measurement of true tectonic motions which have rates of 10 14 s 1 requires extremely high instrument stability but more rapid motions tides and seismic waves apart are even smaller and not much more easily detectable much past effort has been spent improving the transducers used in these instruments which usually measure small displacements the commonest choices are optical the most accurate capacitive the most sensitive and inductive the most rugged nowadays building a transducer is the easiest part a much harder task equally important to a good design is attaching the instrument to the ground so that it can detect the signal wanted this part of the design includes choosing a location a large underground opening is thermally stable but distorting a surface installation is easy to build but noisy because of soil weathering and a borehole is inaccessible to weather but also to the operator all such installations and indeed the whole field of strain and tilt measurement of course rely on the assumption that the deformations of interest can be measured over baselengths of a few hundred meters or less this is true for tides and seismic waves but unproven for tectonic motions appropriate attachment techniques differ for each location and many mundane details such as cementing techniques for borehole instruments remain to be worked out the goal of measuring tectonic and tidal tilt has created many tiltmeter designs most are relatively small instruments that use some form of pendulum or bubble level a few use a liquid surface to measure tilts over a long baseline repeated experience has shown the latter type when well built to be superior to the former proving end monument motions to be a dominant source of noise the same appears to hold true for strainmeters the best results coming from long base laser instruments though strainmeters using rigid or flexible material length standards are useful for special purposes and borehole instruments show promise because achieving a good design has been so difficult it is important to select the goals an instrument must meet and be prepared to compromise on others the difficulty of validating results from this type of instrument makes comparison tests essential such tests as have been made so far show that good results cannot be gotten at low cost or without careful attention to details