volcano monitoring by microgravity and energy budget analysis microgravity monitoring of active volcanoes can provide evidence of sub surface mass and or density changes that precede eruptions if in addition precursory increases in thermal emissions are observed an integrated mechanistic model for volcanic activity may be developed with the potential for forecasting eruptions crater lake volcanoes provide an interesting target for such studies since thermal output can be monitored simply through lake water calotimetry here we summarize 10 years of gravity and thermal data from poas volcano costa rica mass energy balance calculations demonstrate that in the steady state the large thermal inertia of the crater lake acts as a buffer to short term changes in the energy input from the cooling magma feeder pipe since february 1986 it is postulated that there has been gradual emplacement of a shallow magma intrusion associated with vesiculation and gas loss to the surface this follows from unambiguous gravity increases constrained by elevation control that are coincident in time with a period of long term increased energy input to the crater lake progressive reduction of the lake volume by evaporation seepage culminated in an april 1989 ash eruption providing a good documented record of combined gravity and thermodynamic precursors to volcanic activity

upwelling and cyclonic regimes of the near surface circulation in the santa barbara channel the observed near surface circulation in the santa barbara channel indicates in particular two patterns a dominant cyclonic circulation mode and a less frequent upwelling flow mode to explain the dynamics that may govern these two flow regimes momentum balance from a hindcast model of currents in the channel forced by observed hourly winds and hydrographic data was calculated the along channel balance was found to be between wind which was eastward i e equatorward sea level tilt which was westward i e poleward and coriolis which was westward if the wind was 1 intense west and east of the channel and was eastward if the wind was 2 weaker in the east wind condition 1 produced southward cross channel flow in the midchannel connected by eastward currents upstream downstream along the northern southern coast of the channel while wind condition 2 produced northward cross channel flow connected by cyclonic recirculation in the west and westward inflow in the east it is suggested that the former corresponds to the dynamical balance that may occur in the upwelling flow mode while the latter corresponds to the cyclonic circulation mode

magma chamber below poas volcano costa rica direct field evidence for links between volcanic rocks and contemporaneous subvolcanic intrusions are difficult to establish such links might however be inferred by making physical measurements on a youthful active volcano poas is a small composite volcano elevation 2700 m diameter 20 km which has evolved to its present form by a sequence of caldera and crater forming episodes possibly during the last 5 10 4 y there has been a high level of historic activity from the active crater which is 1 km in diameter and 300 m deep and which contains a hot lake lavas and dominant pyroclastic rocks exposed in the active crater calc alkaline basaltic andesites and andesites poas volcano is therefore typical of those in island arcs and young continental margins gravity measurements show that the volcano has a regional negative bouguer anomaly of amplitudes 100 200 gu upon which is superimposed a closed positive anomaly in the active crater area about 2 km in diameter and with a maximum amplitude of 100 gu this is thought to indicate a 1 km radius cylinder of solid rock of basaltic andesite or andesite composition with a shallow upper surface and extending to a depth of several kilometers the concept of a large shallow magma chamber with a diameter similar to that of the volcano appears not to be appropriate for this volcano

objective maps of near surface flow states near point conception california abstract objective streamfunction and velocity potential maps of three commonly observed flow states near point conception california are derived from moored current meter and drifter observations the states are defined using current meter data drifter data are sorted by flow state and averaged within spatial bins to resolve their spatial structures spatial correlations of drifter data show the along shelf and cross shelf decorrelation distances are approximately 45 and 25 km respectively this information is used to make the objective streamfunction and velocity potential maps the total velocity is represented as the sum of the rotational nondivergent streamfunction component and the irrotational divergent velocity potential component the velocity derived from the streamfunction is much stronger than that derived from the velocity potential the streamfunction is sufficiently well resolved to make meaningful vorticity maps the velocity potential indicates a source term in the western santa bar

flow around a coastal bend a model of the santa barbara channel eddy a steady equatorward wind stress is applied over a two layer ocean infinitely deep lower layer west of an otherwise straight meridional coast with a right angle bend initial t 10 days response consists of an equatorward current kelvin wave that triggers a cyclone around the bend through viscous production and advection of vorticity a process akin to eddy shedding in flows without rotation the response at large times is governed by a kelvin wave forced by the equatorward weakening of the assumed positive wind stress curl which produces a poleward current near the coast application to the santa barbara channel cyclone is discussed and the cyclone formation process is further demonstrated with a three dimensional model with topography and stratification

the circulation and water masses in the gulf of the farallones abstract six adcp and ctd ship surveys of the continental shelf and slope in the vicinity of the gulf of the farallones ca were conducted in 1990 1992 adcp data provide much more detail on the structure of the currents over the slope and shelf in the gulf and reveal a persistent largely barotropic poleward flow with a complex mesoscale flow field superimposed the directly measured currents are not well represented by the geostrophic velocity fields derived from hydrographic casts important upper ocean circulation features include a slope countercurrent scc variable shelf circulation and submesoscale eddy like features the scc was present in all seasons and is believed due to a strong year round positive wind stress curl enhanced by point reyes its flow was poleward throughout the upper 300 m and often surface intensified poleward transport in the upper 400 m was 1 3 sv much greater than previous geostrophic estimates for the california current system constrained to a 500 dbar reference level the shelf circulation was much more variable than the scc and generally exhibited a pattern consistent with classic ekman dynamics responding to synoptic wind forcing submesoscale vortices or eddies often dominated the general flow field these eddies are thought to be generated by the frictional torque associated with current topography interactions their centers typically have a distinct water type associated with either the scc or the southward flowing california current higher spiciness anomalies representing a higher percentage of pacific equatorial water pew were typically found in the core of the scc or within anticyclonic eddies lower bland spiciness anomalies characteristic of a higher percentage of pacific subarctic water psaw were associated with cyclonic eddies while these circulation features were largely barotropic the flow also adjusted baroclinically to changes in the density field as different water types were advected by the general flow field or by mesoscale instabilities in the large scale boundary currents as they interacted with topography despite a seasonal cycle in regional wind and ocean temperature time series there is no obvious seasonal pattern in the circulation most of the temporal variability in the current appears to be due to synoptic and interannual variations in atmospheric forcing because of the very dynamic three dimensional nature of the regional circulation the gulf of the farallones is likely to be a center for active mixing and exchange between the coastal and california current waters relative to most us west coast locales

a mechanism for enhanced upwelling off central chile eddy advection 1 a regional numerical model is developed for the mid chile shelf and ocean circulation 30 s to 43 s the model is forced with mean summertime wind stress and transports from a global model over the first 10 days deep 250 300 m peru undercurrent puc water is upwelled to depths of 170 270 m after this time upwelling by the steady winds is largely shut down and a 55 km diameter cyclonic eddy is found to grow in deep water off punta lavapie the mechanism for eddy growth is identified to be baroclinic instability of an initial offshore meander of the equatorward chile coastal current ccc over a period of more than 100 days the onshore arm of the deep water eddy upwells puc water to depths of 150 m toward the shelf a shallow headland eddy then sweeps this puc water to depths of less than 50 m and into the gulf of arauco the net upwelling of 200 m is the largest found for the region observational evidence is cited for the existence of the deep water cyclonic eddy over a period of 4 months a spatially intermittent puc is also found to lie below the ccc in agreement with observational studies the model also predicts the existence of an offshore branch of the ccc that is directed to the northwest

modeling studies of the coastal circulation off northern california statistics and patterns of wintertime flow we conduct modeling studies of the coastal circulation off northern california in the vicinity of the eel river 40 6 n the site of the 1995 2000 strata formation on margins strataform marine geology observational program using a series of nested hydrostatic primitive equation models to aid in the understanding of the shelf flow field that receives and transports sediments during the winter floods the basic objectives of our numerical studies are to model the continental shelf and slope flow and to understand the dominant dynamical processes we simulate the shelf and slope flow surrounding cape mendocino during 100 days in winter 1996 1997 using a 3 km resolution model embedded in a 9 km resolution regional model of the north pacific ocean the naval research laboratory s pacific west coast pwc model the validity of the model simulations is assessed by comparison with current measurements from a strataform shelf tripod outfitted with an acoustic doppler current profiler and with satellite altimetry good agreement is found between the amplitude and time variability of the 3 km resolution modeled and observed alongshore currents on the shelf the 3 km resolution model outperforms the 9 km resolution pwc model using statistical maps of flow variables strong alongshore variability in wintertime flow is documented the role of the forcing supplied by wind and river runoff in establishing this flow asymmetry between regions north and south of cape mendocino is examined using empirical orthogonal functions the evolution of a robust anticyclonic eddy over the shelf and slope adjacent to cape mendocino is described the eddy forms when strong poleward winds weaken and reverse direction during winter storms the important role of alongshore pressure gradients in the shelf circulation is documented

circulation in the point conception santa barbara channel region during spring and early summer 1983 fifteen current moorings were deployed around the periphery of santa barbara channel and over the continental shelf to the west off point conception data from these moorings have been used to describe the regional circulation and to address problems of wind forcing and the spatial coherency scales for current fluctuations the mean circulation in santa barbara channel was dominated by a westward jet which occupied the northwestern portion of the channel current and temperature fluctuations were generally well correlated among all locations around the channel and time lags suggested cyclonic propagation of events around the channel the time fluctuations were dominated by a relatively few low frequency events it was impossible to determine exactly either the driving mechanisms for these events or their relationships to regional flow the flow regime was considerably different off point conception than in the channel locally wind driven upwelling was observed in both the mean and fluctuating flows and the time scales of current variability i e spectral shapes mimicked those of the local winds a dramatic change in the regime off point conception occurred in late may before the transition currents and sea levels had been well correlated in time with both local and remote winds after late may the relation to fluctuating winds was less clear and the alongshore structure of sea level variability had changed radically

transient eddy formation around headlands eddies with length scales of 1 10 km are commonly observed in coastal waters and play an important role in the dispersion of water borne materials the generation and evolution of these eddies by oscillatory tidal flow around coastal headlands is investigated with analytical and numerical models using shallow water depth averaged vorticity dynamics eddies are shown to form when flow separation occurs near the tip of the headland causing intense vorticity generated along the headland to be injected into the interior an analytic boundary layer model demonstrates that flow separation occurs when the pressure gradient along the boundary switches from favoring accelerating to adverse decelerating and its occurrence depends principally on three parameters the aspect ratio b a where b and a are characteristic width and length scales of the headland h cda where h is the water depth cd is the depth averaged drag coefficient and uo a where uo and are the magnitude and frequency of the far field tidal flow simulations with a depth averaged numerical model show a wide range of responses to changes in these parameters including cases where no separation occurs cases where only one eddy exists at a given time and cases where bottom friction is weak enough that eddies produced during successive tidal cycles coexist interacting strongly with each other these simulations also demonstrate that in unsteady flow a strong start up vortex forms after the flow separates leading to a much more intense patch of vorticity and stronger recirculation than found in steady flow

effects of small scale wind on coastal upwelling with application to point conception a three dimensional limited area ocean general circulation model is used to study the response of the coastal ocean to small scale wind forcing the model considers an idealized forcing of a semi infinite upwelling favorable wind with a large positive wind curl at one end such a wind pattern is commonly found in the vicinity of capes and points where the synoptic scale wind is disturbed by coastal mountain ranges the model study includes both process and hindcast studies the process study considers the upwelling spinup and relaxation driven by a positive wind curl it also examines the model sensitivity to wind patterns and an external pressure force the model results show that a strong poleward alongshore pressure gradient is set up by a positive wind curl this pressure force drives an inshore poleward current into the upwelling region during active wind forcing and it causes a surge of warm water into the upwelling zone during wind relaxation the hindcast study is applied to the 1983 organization of persistent upwelling structures opus observations near point conception off central california the simulation uses an idealized geometry but with observed winds during opus a sudden reversal of the surface equatorward currents occurred in the midst of a steady upwelling favorable wind this unexpected coastal flow feature was faithfully reproduced in the model simulation

sensitivity of coastal currents near point conception to forcing by three different winds ecmwf coamps and blended ssm i ecmwf buoy winds previous observational and modeling studies have indicated the importance of finescale winds in determining the circulation near point conception in the santa maria basin smb and the santa barbara channel sbc california there has not been a systematic attempt however to analyze and quantify the sensitivity of the near surface circulation to different wind data here a regional circulation model of the smb and sbc is driven using three wind datasets the european centre for medium range weather forecasts ecmwf 110 km 110 km horizontal grid the coupled ocean atmosphere mesoscale prediction system coamps 9 km 9 km horizontal grid and a blended wind product that combines special sensor microwave imager ssm i ecmwf and buoy and coastal wind data and that is referred to as seb a springtime period march may 1999 in which equatorward wind dominates and wind stress curls are strong is chosen for the study two groups of experiments are conducted with and without assimilating moored temperature observations the focus is on long time scales of greater than weeks and on mean currents comparisons between these experiments and between model and observation show that the circulation driven by the ecmwf wind is much weaker than that by the other two winds on the other hand the seb dataset shows locally intensified wind stress curls behind capes and coastal bends whereas these wind stress curls are weak in coamps it is found that these small scale variations in the wind field force alongshore inhomogeneous pressure gradients that in turn can significantly affect the near coast currents the result is that modeled currents forced by seb agree better with observations than do those produced by coamps empirical orthogonal function analyses were conducted on the near surface currents sea level wind and wind stress curl the mode 1 current 40 is unidirectional i e generally equatorward or poleward and correlates well with the mode 1 wind 90 the mode 2 current 20 is cyclonic in the sbc and poleward inshore and equatorward offshore in the smb it correlates well with mode 1 sea level 70 which suggests that mode 2 currents are driven by the pressure gradient it is significant that neither mode 2 current nor mode 1 sea level correlates well with mode 1 wind stress curl 70 rather they correlate well with the time integral of the mode 1 wind stress curl these conclusions support a previous theoretical idea that cyclonic circulation in the sbc and the inshore currents of the smb are both driven by alongshore pressure setup induced by the time integral of the wind stress curl rather than by the wind stress curl itself this idea of a pressure setup is consistent with the differences found between the currents driven by coamps and seb winds

a curious relationship between the winds and currents at the western entrance of the santa barbara channel 1 relationships between the surface winds and acoustic doppler current profiler adcp currents at 20 levels 25 to 329 m at the western entrance of the santa barbara channel sbc at national data buoy center ndbc buoy 46054 are evaluated for the 1 year period from 1 june 1996 through 31 may 1997 using a relatively new technique for correlating vectors gaps in the data were filled and the resulting time series examined to insure that the statistical properties of the edited data had not been significantly altered vertical current profiles averaged over the year indicate that the mean signal although well defined is smaller than the variability about the mean vertical profiles of current speed and direction suggest the possibility of at least a two layer system of circulation in the sbc with flow between 25 and 180 m being to the ssw and flow from 260 to 329 m being to the ene in agreement with previous results because of the existing dynamical balances the currents are oriented approximately sw ne and the direction of the vertical current shear i e the thermal wind is essentially constant with depth thus warmer waters lie to the north and west and colder waters essentially south of the buoy are consistent with observed cyclonic circulation at the western entrance of the channel vector correlations over the entire year indicate that the winds and currents are poorly correlated consistent with previous results however correlations between the winds and currents below180 m increase noticeably with increasing depth a result which was not anticipated the surface winds and near surface currents in the sbc have repeatedly shown a seasonal connection between january and april and often into may our results show the same pattern and further quantify the strength of this relationship contrary to previous results however we find a relationship between the winds and currents during this period that extends well below the near surface region down to at least 300 m vector correlations between the currents per se at different levels show quite different patterns over time suggesting the influence of independent in water sources of variability finally lagged vector correlations were calculated at four depths 21 41 121 and 313 m for two 3 month periods the first from october through december 1996 a period when a strong connection between the winds and currents was not expected and the second during the spring february through april 1997 when it was expected for the first case correlations increased after the first inertial period at 25 m and 41 m at 313 m an immediate response i e maximum response at zero lag was observed with maximum correlations decaying rapidly over the first inertial period during the spring an immediate response at all four depths similar to the response observed at 313 m during the first period was observed these results imply the importance of the inertial period as a relevant time scale satellite imagery reveals a major frontal zone often located in the vicinity of the buoy vertical sections of temperature and velocity along the axis of the sbc from the princeton ocean model suggest that upwelled waters flowing into the channel from the nw are subducted below the warmer waters that flow through the channel from the east at a location probably not far from the surface front seen from space these model results are consistent with the argument that the higher correlations below 180 m together with a rapid response to wind forcing occur because the deeper waters in the sbc have had recent contact with surface winds prior to their entry into the sbc i e good short term memory lower correlations at intermediate depths 25 180 m for waters flowing to the west may occur because they do not have direct contact with the surface wind due to the presence of a shallow 25 m surface layer and that their motion is partially guided by the channel itself and driven by advective forces outside the sbc

a nested grid ocean model with application to the simulation of meanders and eddies in the norwegian coastal current oceanic flow phenomena vary in such large ranges of time and spatial scales that even with the fastest and largest computer to date one cannot at reasonable costs compute large scale circulation and at the same time resolve mesoscale features like fronts and or eddies yet these features are dynamically important and their inclusion may determine how well we can model the mean flow including the deep ocean circulation a two way interactive nested grid primitive equation model is developed here for coastal ocean applications notable features of the model are 1 nesting can be specified on any subregion of a coarse grid large domain and there can be more than one nest if required 2 the nested region can be hot started from earlier calculation results of the coarse grid region that is the code automatically by a change of an input flag generates topography wind forcing climatology currents density and other prognostic variables in the nest and steps forward in time 3 a time splitting integration with small timesteps in the nest and large timesteps in the coarse grid domain is used and 4 nested variables are driven by coarse grid solutions around the nest s boundaries where a flow relaxation scheme may be used and at the same time drive the coarse grid evolution through its averaged action in the overlapped region to demonstrate its robustness the model is applied in a february march 1988 real time simulation of meanders and eddies in the norwegian coastal current initialized from a 585 days quasi equilibrium calculation the simulation includes meteorological forcings inflows outflows across the open boundaries inflow of the north atlantic warm water in particular tides coastal and baltic discharges and wintertime hydrography for depths 500 m from march 20 to 31 the development of a meander between the froya and the halten banks is simulated the timing and location of the meander agree well with observed hydrography

a forcing mechanism for the poleward flow off the southern california coast it is shown that when the wind distribution along a coast is anisotropic such that its cross shore scale is smaller than its alongshore scale the coastal sea level or the upper layer anomoly a of an ocean forced by both wind and wind curl is governed by a modified nondimensionalized kelvin wave equation a t a y k0 0 y t k1 y dtl where k0 and k1 are wind stress and wind stress curl at the coast respectively y is the alongshore distance and t is the time numerical experiments from a simple reduced gravity type with idealized forcing and coastline to a three dimensional primitive equation model with a realistic coastline bottom topography of the southern california bight and the santa barbara channel and observed wind stresses were carried out to show that the observed near coast near surface poleward flow in the region is primarily forced by the equatorward weakening of the wind curl k1 y 0 in the bight beta provides natural damping by weakening and widening the current through westward propagating rossby waves and causes the current to lead the coastal pressure field by 1 2 months which improves the agreement with observations of the phasing of the modeled currents but is otherwise not required in forcing the poleward flow

water mass analysis and alongshore variation in upwelling intensity in the eastern great australian bight 1 a study of climatological and conductivity temperature depth ctd data for 2004 is made to provide a conceptual model of upwelling for the eastern region of the great australian bight in particular the data and other studies provide strong evidence that shelf break upwelling is confined to the southwest kangaroo island region and does not occur farther to the west off the eyre peninsula rather the upwelled water is likely to remain in a kangaroo island pool until subsequent upwelling events draw the water to the shallower and surface coastal regions of the eastern bight in this manner the surface upwelling apparent off the bonney coast kangaroo island and the eastern great australian bight gab can appear to be simultaneous moreover it appears likely that the water within the kangaroo island pool remains nutrient rich support for this model comes from ctd sections collected in 2004 that show that the upwelled signal cool 26 kg m 3 diminishes in width and intensity with increasing distance from kangaroo island the pattern of fluorescence is similar to that for temperature in the upwelled plume and indicates that the kangaroo island pool remains nutrient rich relatively low oxygen concentrations may indicate a previous bloom the warmest water is found near the shelf break along with very low values of fluorescence and relatively higher levels of oxygen suggesting nutrient limited growth of phytoplankton these data also support the notion that the upwelled nutrient rich water is supplied from the kangaroo island pool and not by shelf break upwelling in the eastern gab anomalously salty and fresh water is identified as resulting from evaporation in coastal bays and groundwater aquifer discharge

weathering mantles and their significance for geomorphological evolution of central and northern europe since the mesozoic abstract weathering mantles saprolites are very widespread in central western and northern europe where they form thick near surface residual deposits often in excess of 50 m they vary in the type of weathering the bedrock lithology involved the topographic setting and the age and stratigraphic context this review paper provides information about the distribution and major characteristics of weathering mantles from a number of key areas including the british isles the central european belt of mid mountains and uplands the scandinavian mountains and the fennoscandian shield it also examines the evidence for weathering etched origin of various landforms including boulders tors inselbergs basins and some regional landforms assemblages major types of regionally important weathering mantles include ferrallitic lateritic saprolites kaolinite rich saprolites sandy to grus mantles and various residuals left after partial dissolution of carbonate rocks although dating of weathering mantles is often circumstantial it appears sufficiently precise to argue for various ages of deep weathering mesozoic pre late cretaceous mantles are particularly widespread but there are also early tertiary and miocene saprolites widely present whilst most grus weathering is likely to be of miocene to pleistocene age individual upland areas have been subjected to multiple episodes of weathering whose legacy is the present day co existence of different weathering products continental and shallow marine deposits around the uplands particularly in the north sea and intra continental graben structures are often dominated by quartz and kaolinite pointing to deeply weathered land surfaces as the source areas and extending the record of weathering on the geological time scale they demonstrate that weathering mantles repeatedly formed and were subjected to erosion and new cycles of weathering were initiated we suggest that deep unroofing of basement structures in many parts of europe has been mainly accomplished by deep weathering and stripping of pre weathered rock the phenomenon of deep weathering has been very important for geomorphology etched landforms vary in size from small residual boulders up to regional characteristic landscapes etchsurfaces such as joint valley landscapes of southern sweden or undulating multi convex and multi concave landscapes of many uplands in central europe deep weathering has played a major part in the geomorphological evolution of europe since at least the late triassic and the concept involving long term etching and stripping provides an appropriate framework to describe and explain both erosional landscapes and sediment features

wind stress curl forcing of the coastal ocean near point conception california near point conception california the atmospheric flow separates from the coast and a large wind stress curl results direct spatial wind field observations from 20 aircraft overflights in the spring of 1983 suggest that ekman pumping of on average 4 m day21 contributes to the local dynamics during strong and persistent upwelling events the curl driven ekman pumping reaches up to 20 m day21 a single complex empirical orthogonal function explains more than 72 of the spatial and temporal wind stress variance it reveals large wind stress curl at the center of the western santa barbara channel entrance this dominant mode correlates strongly r 2 5 0 79 with the wind stress observed at a moored buoy the location of largest ekman pumping in the ocean indicated by this mode coincides with the location of a laterally sheared cyclonic flow cold upwelled waters enter the santa barbara channel along its southern perimeter while warm and thus buoyant waters from the southern california bight exit the channel along its northern perimeter buoy wind stress and lateral current shear at 30 m depth correlate significantly at periods of about 3 5 and 6 days with phase lags of about 0 5 and 2 days respectively hydrographic observations from 1983 do not however indicate effects of ekman pumping on the internal mass field as winds vary in speed and direction at daily timescales this contrasts with 1984 observations that do indicate strong doming of isopycnals over the center of the channel at its western entrance winds prior to and during hydrographic observations in the spring of 1984 were both stronger and more steady than they were in 1983 cyclonic shears reach 0 4 f at the entrance of the santa barbara channel near point conception here f is the planetary vorticity the thermal wind balance explains the lateral shear of the alongchannel surface flow rather well

poas volcano costa rica geology of the summit region and spatial and temporal variations among the most recent lavas prosser j t and carr m j 1987 po s volcano costa rica geology of the summit region and spatial and temporal variations among the most recent lavas in s n williams and m j carr editors richard e stoiber 75th birthday volume j volcanol geotherm res 33 131 146 the recent eruptive history of po s volcano is described here on the basis of field mapping of the summit area this period which may represent 10 to 20 000 years and less than 10 of the history of the volcano began with caldera formation subsequent events included composite cone construction faulting and flank subsidence flank fissure eruption and multiple crater collapses local and regional structures have controlled the locations of summit vents and flank cinder cones chemical compositions of lavas of known stratigraphic position demonstrate temporal magmatic variation at po s three similar felsic to mafic magmatic sequences occurred at the summit the first and second sequences were separated by flank and summit eruptions of a distinct magma batch enriched in tio and p205 the three felsic to mafic sequences appear to be cyclical and the repeated similar variations are interpreted as progressive tapping of zoned magma bodies developed repeatedly from a common parent by similar crystal fractionation processes the breaks between the three sequences correlate with shifts or major modifications of the eruptive center the chemical composition of the most recent lava erupted in 1954 indicates that the volcano is near the end of the present sequence the lavas are calc alkaline basalts and andesites that are similar to the mafic lavas that comprise the bulk of the central american volcanic front the samples can be divided into 3 spatial temporal geochemical groups a summit group that represents the most recent activity a tio2 rich group that erupted primarily on the south flank about 7500 yr b p and an al203 rich group that erupted primarily from vents north of the presently active main crater geochemical variations and projections into pseudoternary cmas diagrams suggest a moderate pressure for the summit group that is a magma chamber at intracrustal to subcrustal depths the al203 rich group define smaller primary phase volumes for olivine and plagioclase which suggests a deeper and or more water rich magma chamber the tio2rich group appears to be a batch of mixed magma with the summit group magma as one endmember and a less siliceous magma as the other

data assimilation model study of the santa barbara channel circulation the seasonal circulation in the santa barbara channel sbc consists of a cyclonic eddy in the western basin and a poleward current along the northern coast in this study the monthly mean circulation is simulated using a three dimensional primitive equation model with data assimilation included the data are derived from the santa barbara channel and santa maria basin coastal circulation study covering an 8 month period from january to august 1994 the 6 hourly moored temperature observations in the upper 100 m water column are continuously assimilated into the model using a local correction method although salinity and wind forcing are not explicitly included comparisons with the observations indicate that the model results generate realistic flow and temperature structures inside the sbc the assimilation model faithfully reproduces the cyclonic eddy but it fails to predict the currents at the exits of the channel the issue of the data need is addressed through a sensitivity study

subtidal energetics in the faroe shetland channel coarse grid model experiments this paper compares various forcings that contribute to the regional subtidal energetics of the ocean passageway northwest of scotland in the faroe shetland channel fsc where inflow of warm and saline north atlantic water mixes with outflow of cold and less saline nordic sea waters on the scales resolvable by the coarse grid sizes of x y 20 km and 20 vertical sigma layers changes in currents energetics caused by wind atlantic inflow doubled decreased horizontal mixing surface heat flux and open boundary density specifications were 28 43 40 16 and 5 respectively of the kinetic energy of a background quasi steady slope current the subtidal currents were not sensitive to the atmospheric pressure forcing and the surface relaxation to monthly climatology nor to the inclusion of additional apart from m2 tidal constituents k1 o1 and s2 wind induced motions resulted in transport fluctuations of about 1 5 sv in the fsc maximum in winter and minimum in summer and alongshore and cross shore current variances of 0 1 and 0 05 m s 1 respectively in fair agreement with observations spectral peaks at periods of 23 30 hours were found and were shown to correspond to resonant continental shelf waves in the channel