tectonic and structural evolution of gough volcano a volcanological model abstract morphostructural stratigraphic and tectonic data indicate that the evolution of gough volcano is similar to other oceanic intraplate volcanoes is older than 1 ma and is related to a transform fault at least six evolutionary stages can be distinguished within two major magmatostructural periods dominated by basaltic and trachytic magmas respectively the basaltic shield volcano is characterized by a curved elongated shape in plan and a rift zone with a high density of dykes combined with a radial intrusive system the latter is interpreted as being fed by a magma chamber some 4 km below the surface the activity of the volcano became more centralized at the end of the basaltic period and its slopes became steeper this corresponds to the development of a shallower and narrower central conduit in the edifice the basaltic period was terminated by formation of a shield caldera related to the 4 km deep magma chamber the term shield caldera is used for a collapse structure that is postmagmatic large in comparison with the diameter of the volcano and delimited by normal faults that do not show a closed circular pattern but rather a series of arcs in contrast summit calderas are defined as smaller circular shaped centrally situated synmagmatic features related to a central shallow column during the basaltic period landslides were generated on the flanks of the edifice as a result of slope stability factors which are not easy to determine at present and dynamic factors among which the intrusion of magma along a curved zone certainly played a major role the trachytic period is characterized by comparatively rare pyroclastic deposits and a large volume of thick flows extruded from domes these extrusions as well as plugs formed from vertical cylindrical columns of magma rising from shallow individual magma pockets fed by the main reservoir

deep magma body beneath the summit and rift zones of kilauea volcano hawaii a magnitude 7 2 earthquake in 1975 caused the south flank of kilauea volcano hawaii to move seaward in response to slippage along a deep fault since then a large part of the volcano s edifice has been adjusting to this perturbation the summit of kilauea extended at a rate of 0 26 meter per year until 1983 the south flank uplifted more than 0 5 meter and the axes of both the volcano s rift zones extended and subsided the summit continues to subside these ground surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones kilauea s magmatic system is therefore probably deeper and more extensive than previously thought the summit and both rift zones may be underlain by a thick near vertical dike like magma system at a depth of 3 to 9 kilometers

upper quaternary palaeoclimates of the mar chiquita area north pampa argentina abstract the mar chiquita shallow lake is the largest water body in argentina located in a quaternary tectonic depression 30 45 s and 62 30 w the southern margin of the depression is dominated by fluvial sediments transported by the rio segundo and aeolian deposits a 65 km wide alluvial fan is the most significant geological unit the sequence of climatic events in the area is i upper pleistocene dry period is4 development of a large sand sea ii complex upper pleistocene humid period is3 first phase of pedogenesis on the aeolian landforms and fluvial deposits marull sands general dissipation of the inherited relief carcarana fm and probable formation of the large alluvial fan lagunilla del plata fm second phase of pedogenesis in a flat landscape during this phase the mar chiquita lake acted as local base level iii late pleistocene dry period is2 lgm deposition of a loess mantle on the surface of the fan tezanos pinto fm iv a subhumid phase 16 000 yr bp redistribution of sand dunes lomita del indio fm and precipitation of pedogenic carbonates in the loess development of a fluvial terrace v younger dryas s l development of deflation hollows associated with lunettes vi hypsithermal humid period general pedogenesis rise of the lake level vii upper holocene dry period deposition of a loess sheet san guillermo fm formation of deflation hollows viii little ice age reduction of the lake surface area and formation of a dune field campo maare sands

comparison and cross checking of historical archaeological and geological evidence for the location and type of historical and sub historical eruptions of multiple vent oceanic island volcanoes

late quaternary paleosols stratigraphy and landscape evolution in the northern pampa argentina the field properties micromorphology grain size geochemistry and optically stimulated luminescence osl ages of two late quaternary sections have been used to reconstruct the sequence of pedosedimentary processes and to provide insights into landscape evolution in part of the northern pampa of argentina paleosols developed in paludal sediments adjacent to the parana river at baradero and in loess at lozada can both be correlated and linked to other sites thus enabling for the first time the tentative recognition and tracing of a diachronous soil stratigraphic unit that probably spans the equivalent of at least part of marine oxygen isotope stage ois 5 the paleosol at lozada was truncated and buried beneath fluvial sediments during the time span of ois 4 and 3 eolian gradually replaced paludal inputs at baradero over this period and there were also two clearly defined breaks in sedimentation and development of paleosols the period corresponding to ois 2 was marked by significant loess accumulation at both sites with accretion continuing into the mid holocene only at lozada the more developed nature of the surface soil at baradero probably reflects a combination of a moister climate and a longer soil forming interval

modelling of surface ground deformations in the phlegraean fields volcanic area italy a preliminary finite elements model of the ground deformations observed at phlegraean fields is proposed the model assumes an oblate spheroid magma chamber at the depth of 5 4 km with major semiaxis of 1 5 km and minor semiaxis of 0 75 kin the dimensions of the magma chamber have been evaluated by using a thermal model based on the assumptions that a progressively cooling huge magmatic body is responsible for the volcanic activity at phlegraean fields in the last 35 000 years surface deformations caused by an overpressure of 30 mpa in the magma chamber have been calculated constant and temperature dependent elastic parameters of the surrounding medium have been considered vertical displacements of the order of those presently observed at phlegraean fields can be obtained only with temperature dependent elastic properties of the medium

seismicity induced by gas production ii lithology correlated events induced stresses and deformation a 3d relocation technique permits precise locations of induced earthquakes geostatistical processing using the data of 87 boreholes provides the basis of a precise 3d structure with a dome geometry conventional laboratory mechanical tests performed on deep rock samples 1000 m to 5000 m define the rock properties at depths similar to those of the seismic events 1 ml 4 2 that range from 1 to 7 km

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

thermodynamics of water permeated unwelded pyroclasts 1 equilibrium properties abstract we report here the results of an investigation of thermodynamic equilibrium properties of systems constituted by phlegraean unwelded pyroclasts dry or saturated with water we have experimentally measured the porosity of samples of phlegraean rocks and determined the values of the heat capacity and of thermal expansion of dry and water perfused tuffs having different texture structures also the energetics of the process of adsorption of water on the large internal surface of these porous materials has been investigated the amount of heat exchanged during the reversible formation of an adsorbed layer has been determined in dependence of its thickness and as a function of temperature the coherent picture emerging from the ensemble of all these measurements is that of a direct connection between the processes of adsorption desorption and the stress of the porous rock in very unsaturated soils these processes may constitute a much more efficient mechanism of transformation of thermal energy into soil deformation compared with that of thermal expansion of the solid matrix

seismic source mechanism of degassing bursts at kilauea volcano hawaii results from waveform inversion in the 10 50 s band the current march 2008 to february 2009 summit eruptive activity at kilauea volcano is characterized by explosive degassing bursts accompanied by very long period vlp seismic signals we model the source mechanisms of vlp signals in the 10 50 s band using data recorded for 15 bursts with a 10 station broadband network deployed in the summit caldera to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous medium that takes topography into account the vlp signals associated with the bursts originate in a source region 1 km below the eastern perimeter of halemaumau pit crater the observed waveforms are well explained by the combination of a volumetric component and a vertical single force component for the volumetric component several source geometries are obtained which equally explain the observed waveforms these geometries include 1 a pipe dipping 64 to the northeast 2 two intersecting cracks including an east striking crack dike dipping 80 to the north intersecting a north striking crack another dike dipping 65 to the east 3 a pipe dipping 58 to the northeast intersecting a crack dipping 48 to the west southwest and 4 a pipe dipping 57 to the northeast intersecting a pipe dipping 58 to the west southwest using the dual crack model as reference the largest volume change obtained among the 15 bursts is 24 400 m3 and the maximum amplitude peak to peak of the force is 20 gn each burst is marked by a similar sequence of deflation and inflation trailed by decaying oscillations of the volumetric source the vertical force is initially upward synchronous with source deflation then downward synchronous with source reinflation followed by oscillations with polarity opposite to the volumetric oscillations this combination of force and volume change is attributed to pressure and momentum changes induced during a fluid dynamic source mechanism involving the ascent expansion and burst of a large slug of gas within the upper 150 m of the magma conduit as the slug expands upon approach to the surface and more liquid becomes wall supported by viscous shear forces the pressure below the slug decreases inducing conduit deflation and an upward force on the earth the final rapid slug expansion and burst stimulate vlp and lp oscillations of the conduit system which slowly decay due to viscous dissipation and elastic radiation consideration of the fluid dynamic arguments leads us to prefer the dual crack vlp source model as it is the only candidate model capable of producing plausible values of length scales and pressure changes the magnitudes of the vertical forces observed in the 15 bursts appear consistent with slug masses of 104 to 106 kg

estimation of evapotranspiration losses in the vadose zone using stable isotopes and chloride mass balance method this study used stable isotope and chloride data of porewater to evaluate water fluxes through the vadose zone and thereby estimate evapotranspiration water losses in parts of the nabogo catchment of the white volta basin in ghana the overall objective was to develop a framework so that the recharge regime can be properly conceptualized for numerical hydrological modeling unsaturated zone material was sampled at regular intervals of 50 cm to a maximum depth of 300 cm in four different locations in the study area rainwater groundwater and surface water were simultaneously sampled and analyzed for their 18o and 2h characteristics porewater extracted from the unsaturated zone material was analyzed for the 18o and 2h and chloride content and profiles were created to gauge the isotopic evolution of precipitation and estimate evaporative losses at each interval of the sampling the chloride mass balance technique was used to estimate the fraction of infiltrating water remaining at each interval of the sampling transpiration losses through the entire profile were then estimated this study finds that the vertical infiltration of water through the vadose zone is dominated by piston flow and a mixture of piston and preferential flows in the shallow subsurface 0 0 3 0 m evaporative losses estimated from stable isotope data fall in the range of 29 3 52 4 322 3 576 4 mm year of the annual precipitation with an average of 40 or 440 mm year estimated vadose zone recharge at the maximum depth of sampling ranges between 11 1 and 185 mm year with an average of 32 9 mm year representing 1 1 18 5 and 3 29 of the annual precipitation respectively estimated transpiration losses within this interval range between 29 1 290 mm year and 69 5 695 mm year with an average of 54 7 547 mm year of the annual precipitation transpiration losses appear to increase down the profile and apparently account for a significant percentage of water losses in the vadose zone a significant proportion of the original precipitation is lost within the upper 300 cm 3 m of the vadose zone the water table fluctuations method was independently used to estimate saturated zone groundwater recharge and indicates that recharge rates range between 64 65 and 151 2 mm year with an average of 102 5 mm year which respectively represent 5 9 13 7 and 9 3 of the average annual precipitation in the area the apparently higher estimates from the water table fluctuations method may arise from uncertainties in the specific yield values used for the vadose zone material

precursors to the kalapana m 7 2 earthquake the kalapana hawaii earthquake of november 1975 had a rupture length of 40 to 50 km and was located on the south flank of the active volcano kilauea the source mechanism was dip slip normal faulting on a plane dipping 20 degrees to the se with the greatest principal stress oriented in that direction and accumulated by volcanic intrusions into kilauea s rifts the source area of the 1975 earthquake was subject to intensive geological and geophysical research for many years before this earthquake because of its proximity to the volcano we studied the distribution of epicenters for small earthquakes from 1962 to 1975 seven seismographs located within 3 km of the aftershock area had been in operation for 3 to 10 years before the mainshock and geodetic triangulations and trilaterations in the source area had been carried out repeatedly since 1914 we found that precursory changes occurred throughout most of the rupture area but in two distinctly different patterns in the larger outer anomalous area the seismicity rate was decreased by 50 during the 3 8 years before the mainshock in addition several geodetic lines indicated anomalous strain release during this time within two inner areas the seismicity remained high then increased shortly before the mainshock in one of the inner areas a p wave travel time delay of 0 2 s could be detected which began about 3 5 years before the mainshock within the other inner anomalous area geodetic strain was accumulating until the first half of 1975 when 3 5 10 4 strain 35 bars was released aseismically by contrast the outer anomalous volume was experiencing strain softening from 1970 1971 on we interpret these observations as indicating that strain softening by fault creep in the outer anomalous area transferred stress into two major asperities locked portions of the fault a velocity decrease and foreshocks were observed in one asperity and high stress accumulation in the other implying that dilatancy of the crust probably occurred our model is qualitatively supported by the independent evidence of strong motion records which show that the kalapana earthquake was a complex multiple rupture we conclude that the kalapana earthquake was preceded by a preparatory process which lasted 3 8 0 3 years and which had dimensions of 45 10 km covering approximately the aftershock area

a fluid filled fracture as possible mechanism of ground deformation at phlegraean fields italy two uplift episodes have recently been recorded at phlegraean fields a volcanic region near naples south central italy the first episode occurred in 1970 and lasted up to 1972 the second has begun at the end of 1982 and is still in progress an attempt to model the ground deformations which occurred during the 1970 1972 event is made in this paper the source has been assumed to be a two dimensional fluid filled fracture similar to a sill a good fit with experimental data has been obtained for a short 1 2 km long shallow 3 km deep source and a driving pressure ranging from 60 to 210 bars rigidity values have been fixed at 3 5 4 0 1010 c g s with poisson ratio equal to 0 3 this solution which differs from previous approaches bymogi 1958 andwalsh anddecker 1971 is non unique but the present results are in good agreement with observed horizontal and vertical displacements notwithstanding the oversimplification made in assuming a homogeneous elastic semi infinite medium the predicted stress field seems to be in agreement with the fault plane solutions and the pattern of epicenters determined for the uplift seismic swarm episode that is still in progress

tectonics of marion and prince edward volcanoes indian ocean result of regional control and edifice dynamics abstract a structural analysis of marion and prince edward islands shows two kinds of tectonic control 1 1 regional tectonics the parallelism between a common structural trend on these two islands characterized by a n20 e and e w association the morphology of the underlying submarine plateau the structure of the sea floor and the fact that both islands display the same rhythm of activity all suggest that these volcanoes all resulted from the reactivation of oceanic lithosphere paleostructures 2 2 edifice tectonics the marion cone is better suited for a study of edifice dynamics than prince edward volcano of which about 80 has subsided below sea level marion is composed of a main volcanic center and a rift zone on which a second volcanic center developed it is proposed that the weight of the edifice and the geometry of the feeding and intrusive system emanating from small relatively deep magma chambers are responsible for the peculiar dynamic properties of the marion edifice the latter are the absence of a caldera a low rate of activity and numerous flank landslides a three fold classification of the stability of volcanoes based on structural patterns is proposed

paleoenvironmental reconstruction of quaternary valley fill successions in summit paleosurfaces of southern sierras pampeanas cordoba province argentina abstract climatic and environmental changes were inferred from the study of late quaternary sequences that represent paleo valleys filling in the summit pampas at the center south of the sierra de comechingones cordoba province argentina a representative sedimentological section p1 was described and sampled and sediments age 14 c granulometric characteristics and organic matter content were determined in the analyzed succession four main stratigraphic units were recognized and interpreted the stratigraphic and pedological characteristics diatom levels presence geomorphological features and altitude conditions of the study area allow us to conclude that 1 valley fill deposits are holocene from 8310 110 yr bp to present days and composed exclusively of loessic loessoid material from surrounding areas 2 the dominant transport mechanism could have been laminar and or hyperconcentrated flows mainly associated with slope evolution processes sheet flow and high density flows 3 isolated swamps with important biological activity were the dominated environments in to the valleys these environments suggest an alternating pedogenic cycles were the most important was the middle late holocene indicating a landscape stabilization tendency 4330 130 yr bp 4 temperate wet climatic conditions and high seasonality characterized middle early holocene hypsithermal period more arid conditions dominated late holocene from 1500 to 1000 bp to the present temperate wet climatic conditions occurred and this period was interrupted by the little ice age 5 in the mountains both in wet and dry periods the rainfalls were probably higher as well as the temperature must be lower than the surrounding plain especially in winters perhaps reaching periglacial conditions during more arid periods

intrusion and deformation at campi flegrei southern italy sills dikes and regional extension 1 the campi flegrei volcanic district in southern italy has been uplifted since 1968 by a net maximum of 3 m during the intervals 1968 1972 and 1982 1984 the uplift represents a permanent deformation against a background rate of subsidence of about 17 mm a 1 previous models have reproduced the observed vertical deformation but not the full pattern of horizontal movements the 1982 1983 deformation is here reanalyzed in terms of a penny shaped sill on its own with a tabular surface protrusion or in an extensional stress field it can be explained best by the intrusion of a sill of 0 03 0 04 km3 at a depth of 2 75 km in a crust that is being stretched ese wnw at a strain rate of about 5 6 10 5 a 1 the sill s volume is similar to the common volumes of campi flegrei s eruptions since the neapolitan yellow tuff nyt caldera was formed 15 6 ka ago this similarity and the permanent nature of the uplift favor magmatic intrusion as the primary source of unrest sill formation may thus reflect the spreading of magma at a level of neutral buoyancy or along lateral discontinuities in the crust the southern part of the caldera has been shielded from post nyt eruptions despite some 33 m of permanent uplift since roman times precursors to eruptions may thus be related not to caldera wide uplift but to the preceding conditions that determine whether magma ascends beneath the southern part of the caldera favoring sill intrusion or elsewhere favoring an eruption

viscoelastic displacement and gravity changes due to point magmatic intrusions in a gravitational layered solid earth summary we present a method for the computation of time dependent geodetic and geophysical signatures deformation potential and gravity changes due to magmatic intrusions in a layered viscoelastic gravitational medium this work is an extension of a deformation model previously developed to compute effects due to volcanic loading in an elastic gravitational layered media the model assumes a planar earth geometry useful for near field problems and consists of welded elastic and viscoelastic layers overlying a viscoelastic half space every layer can either be considered elastic or viscoelastic the intrusion treated as a point source can be located at any depth in any of the layers or in the half space several examples of theoretical computations for different media are also presented we have found that in line with previous results obtained by other authors introducing viscoelastic properties in all or part of the medium can extend the effects displacements gravity changes etc considerably and therefore lower pressure increases are required to model given observed effects the viscoelastic effects seem to depend mainly on the rheological properties of the layer zone where the intrusion is located rather than on the rheology of the whole medium we apply our model to the 1982 1984 uplift episode at campi flegrei modelling simultaneously the observed vertical displacement and gravity changes the results clearly show that for a correct interpretation of observed effects it is necessary to include the gravitational field in the anelastic theoretical models this factor can change the value and pattern of time dependent deformation as well as the gravity changes explaining cases of displacement without noticeable gravity changes or vice versa cases with uplift and incremental gravity values and other cases the combination of displacement and gravity changes is found to be especially effective in constraining the possible characteristics of the magmatic intrusion as well as the rheology of the medium surrounding it

backscattering and geophysical features of volcanic ridges offshore santa rosalia baja california sur gulf of california mexico abstract volcanic ridges formed by series of volcanic edifices are identified in the central part of the gulf of california between isla tortuga and la reforma caldera santa rosalia region isla tortuga is part of the 40 km long tortuga volcanic ridge tvr that trends almost perpendicular to the spreading center of the guaymas basin the rosalia volcanic ridge rvr older than tvr is characterized by volcanic structures oriented towards 310 following a fracture zone extension and the peninsular slope it is interpreted that most of the aligned submarine volcanic edifices are developed on continental crust while isla tortuga lies on oceanic like crust of the guaymas basin from a complete bouguer anomaly map it is observed that the alignments of gravity highs trending 310 and 290 support the volcanic and subvolcanic origin of the bathymetric highs volcanic curvilinear structures lava flows and mounds were identified from backscattering images around isla tortuga and over a 400 m high virgenes high where the tvr and the rvr intersect a refraction wide angle seismic profile crossing perpendicular to the virgenes high together with gravity and magnetic data indicate the presence of shallow intrusive bodies presumably of basaltic or andesitic composition it is inferred that most volcanic edifices along the ridges have similar internal structures we suggest that the growth of different segments of the ridges have a volcano tectonic origin the older rvr lies along the extension of a fracture zone and it probably is associated with pliocene ne sw extension

the pedosedimentary evolution and chronology of tortugas a late quaternary type site of the northern pampa argentina new micromorphological magnetic susceptibility geochemical and geochronological data have been collected from tortugas a key late quaternary type site of the northern pampa argentina thus enabling the detailed reconstruction of the pedogenic and sedimentary history of this loess paleosol sequence paleosols developed in the ceres formation and the overlying lower member of the tezanos pinto formation retain evidence for leaching bioturbation and particularly clay translocation processes being dominant both paleosols are truncated evidence for water sorting and sediment reworking as well as continued bioturbation and redistribution of carbonates suggests that intervening depositional phases were complex the previously recorded hypsithermal soil developed in the upper member of the tezanos pinto formation has similar characteristics to the buried paleosols yet does not appear to have been truncated at this site and is only covered by a thin layer of sediment san guillermo formation this latter unit has been pedogenically welded onto the hypsithermal soil thus creating the present day surface soil complex a series of optically stimulated luminescence dates from throughout the sequence provide a stratigraphically consistent chronological framework ca 1 150 ka for the pedosedimentary reconstruction yet conflict with the previously reported thermoluminescence based chronology for the site and region ca 1 90 ka

numerical modeling of groundwater resource management options in the east oweinat area sw egypt southwest egypt is an arid area with no surface water and limited resources of useable groundwater in the well known nubian sandstone aquifer system these groundwater reserves have been heavily exploited since the 1960s which has led to substantial decline in the potentiometric surface of the aquifer a calibrated regional numerical model with refined grids on the pumping centers has been used to investigate the hydrodynamic impacts of different groundwater management options on the potentiometry of the aquifers the results indicate that there is a real danger of either dewatering the shallow aquifer in some areas e g kharga oasis or increasing the water depth to uneconomic lifting depth they also indicate that although the planned extraction rates in dakhla farafra and bahariya oases are feasible for at least the coming 100 years the present rate for kharga oasis and the planned rate for the east oweinat area have to be reduced substantially

channel fill and sheet flood facies sequences in the ephemeral terminal river gash kassala sudan abstract detailed facies analysis of the river gash fluvial sediments on two dimensional profiles across and along the main channel has revealed a number of facies and two distinct types of sequences channel fill and sheet flood sequences it seems that each sequence type is produced by specific depositional event and both sequences represent two end members for suite of mixed sequences the facies and sequences show rapid lateral variability and they merge and interfinger with each other they also show partial to complete modification due to subsequent floods and stage variation it seems that the thick sediments of the river gash in the kassala area were produced in two phases first by braided channel aggradation and lateral migration second by both channelized and unchannelized sheet flood deposition deposits of these two phases contribute to the sediments of the present day gash fluvial basin in the kassala area the gash sediments show some similarities and differences to those of ephemeral and low sinuosity braided streams the predominance of sheet flood deposits is consistent with the ephemeral flashy high flow regime in the river gash the non conformity of the river gash depositional style with the braided model of fluvial deposition may be due to this semi arid terminal flashy character which has control on the depositional processes and patterns

groundwater flow modeling and particle tracking for chemical transport in the southern voltaian aquifers groundwater is the major source of water supply for most uses in the rural settlements in ghana a groundwater flow model was calibrated for some aquifers of the southern voltaian sedimentary system under steady state conditions the objective was to determine estimates of the hydraulic conductivities of the different hydrostratigraphic units of the southern voltaian and the distribution of recharge from precipitation data on the stable isotopes of oxygen and hydrogen from the study area suggest that groundwater recharge in the area is from rainfall the calibrated steady state model suggests that aquifer hydraulic conductivities in the study area range from 1 19 to 6 3 m day hydrostratigraphic unit specific hydraulic conductivities are discussed the calibrated recharge ranges from 3 81e 05 m day to 6 0e 04 m day which represents 0 9 6 of the precipitation in the form of rainfall six distinct flowpaths have been defined using particle tracking the particle tracking simulation suggests travel times in the range of 380 to 5 199 years from recharge areas to discharge areas along the flowpaths identified a contaminant dropped at the recharge areas in the central sections of the model area would travel at these rates along the flowpaths assuming that advection is the dominant transport process inverse geochemical modeling indicates the dissolution of albite k feldspars and anorthite respectively along flowpaths i and iv the inverse modeling along flowpaths i and iv suggest the dissolution of albite k feldspar and anorthite respectively at 1 085e 06 3 16e 08 and 3 168e 07 mmol year

modeling the three dimensional structure of macroscopic magma transport systems application to kilauea volcano hawaii we report the results of modeling the three dimensional internal structure of kilauea s magmatic passageways the approach uses a clear plexiglass model containing equally spaced levels upon which well located seismic hypocenters are plotted application of constraining geologic and geophysical criteria to this distributed volume of earthquakes permits the interpretation of seismic structures produced by fracturing in response to locally high fluid pressures four magma transport and storage structures have been identified within and beneath kilauea 1 primary conduit the conduit transporting magma into kilauea s summit storage reservoir rises from the model base 14 6 km to the 6 5 km depth level it is a zone of intense fracturing and inferred intrusion whose horizontal sections are elliptical in planform over its height the average major axis of the component horizontal sections is 3 3 km with an average minor axis of 1 7 km this yields an aspect ratio of 0 52 at the 14 6 km level the strike of the major axis is n67 e during passage from the upper mantle through the oceanic crust this axis rotates in a right handed sense until the strike is n41 w at the 6 5 km level 2 magma chamber complex floor the interval from 6 5 to 5 7 km immediately over the primary conduit is aseismic this suggests differentially high fluid to rock ratios and relatively weak pathways for further vertical transport into higher levels of the storage complex as well as lateral leakage eastward into the mauna ulu staging area for later vertical ascent beneath the upper east rift zone seismicity within the immediately subjacent rocks that form the top of the primary conduit at 6 5 km suggests that this inferred magma rich horizon forms the effective floor of the summit storage complex 3 magma chamber crown intense seismicity over the 1 1 1 9 km depth interval defines an elliptical region in plan view the top of this region has a broad apex with an average major axis of 1 5 km and an average minor axis of 1 1 km producing an aspect ratio of 0 73 this region coincides with the epicentral position of summit vertical displacement maxima during inflationary deformation and is interpreted as a region of intense diking crowning the summit storage complex 4 upper east rift zone pipe from a depth of 5 7 km a cylindrical region of seismicity rises beneath the upper east rift zone to the 1 9 km level where it merges with the subhorizontal upper east rift zone duct this pipe like zone has a mean diameter of 1 4 km and a vertical axis that pierces the surface of the volcano at the intersection of the koae fracture system and the upper east rift zone we suggest this pipe forms a principal connection between the base of the summit storage reservoir and near surface storage compartments and ducts in the upper east rift zone in this role the pipe is suggested to have contributed heavily to mauna ulu s magma supply during 1969 1974 the model of magma transport and storage thus constructed provides a context in which other types of data e g ground deformation and electrical conductivity may be interpreted as well as a means of refining petrological inferences based on lava chemistry

magma reservoirs and neutral buoyancy zones on venus implications for the formation and evolution of volcanic landforms we examine the production of magma reservoirs and neutral buoyancy zones nbzs on venus and the implications of their development for the formation and evolution of volcanic landforms the high atmospheric pressure on venus reduces volatile exsolution and generally serves to inhibit the formation of nbzs and shallow magma reservoirs for a range of common terrestrial magma volatile contents magma ascending and erupting near or below mean planetary radius mpr should not stall at shallow magma reservoirs such eruptions would be characterized by relatively high total volumes and effusion rates for the same range of volatile contents at 2 km above mpr about half of the cases result in direct ascent of magma to the surface and half in the production of neutral buoyancy zones in general neutral buoyancy zones and shallow magma reservoirs begin to appear as gas content increases and are nominally shallower on venus than on earth for a fixed volatile content nbzs become deeper with increasing elevation over the range of elevations treated here 1 km to 4 4 km depths differ by a factor of 2 4 these analyses reveal several factors that may help to account for the low height of volcanoes on venus larger primary reservoirs cause the wide dispersal of conduits building edifices models of the position of the shallow nbz reservoir during edifice growth show that for earth the magma chamber center remains at a constant depth below the growing edifice summit thus keeping pace with the increasing elevation while on venus the chamber center becomes deeper relative to the summit of the growing edifice because of the major change in atmospheric pressure as a function of altitude therefore neutral buoyancy zones and magma reservoirs on venus will remain in the prevolcano substrate longer and in many cases may not emerge into the edifice at all the lower rate of vertical migration implies that magma reservoirs would tend to stabilize undergo greater lateral growth and become larger on venus than earth the proportion of the available magma going into production of the edifice relative to that intruded into the substrate is smaller on venus than earth large reservoirs would encourage multiple and more widely dispersed source vents and large volumes for individual eruptions in large reservoirs positively buoyant materials are likely to be produced from differentiation substrate remelting and volatile exsolution nonbuoyant materials exsolving volatiles in a shallow reservoir will need higher gas bubble concentrations to produce eruptions than on earth and when this gas enriched melt emerges at the surface it is more likely to retain its bubbles than to undergo explosive disruption due to the high surface atmospheric pressure therefore there is the potential for the production of a range of erupted lavas that have very high gas bubble concentrations leading to anomalous more viscous rheological properties inhibition of disruption of volatile rich magma for both basaltic and more evolved compositions can lead to the production of 1 more bubble rich vesicular flows characterized by higher viscosity and greater thicknesses the venus equivalent of effusions that would have lost much of their volatiles in the fire fountaining process on earth 2 high volume high discharge rate extremely gas rich basaltic effusions that increase viscosity considerably upon surface extrusion and produce domes whose volumes are considerably higher than their dense rock equivalent and 3 more evolved compositions that are gas rich but do not undergo disruption upon effusion and produce domes and flows of high viscosity the venus equivalent of terrestrial ignimbrites on the basis of these analyses we predict that intrusions and dike emplacement should be common particularly around both shallow and deep magma reservoirs and the tops of dikes should be manifested as radial fractures there should be a range of diameters of circular features associated with the presence of both shallow nbz related and deep plumerelated magma reservoirs large volume lava outpourings should be favored at lower elevations and shallow reservoirs and edifices should be more common at intermediate elevations at the highest elevations magma reservoirs are predicted to be large and relatively deep with low associated edifices direct ascent of magma where neutral buoyancy zones are unlikely low elevations and the propensity for relatively larger magma reservoirs on venus when they do form are both factors which will tend to favor high volume eruptions independent of variations in magma temperature or chemistry individual volcanic features should be interpreted in terms of regional geologic setting and the dynamics of elevation changes commonly associated with various scales of mantle processes and magma emplacement in order to assess global crustal growth processes on venus

late pleistocene to recent climate change in cordoba province argentina geomorphological evidence abstract repeated episodes of climate change affected the cordoba plains during the late pleistocene and holocene many of the geomorphologic features of cordoba province were developed in response to climatic oscillations and their development can be correlated to changes in precipitation and hydrologic regimes alternating periods marked by dry climate and high evapotranspiration rates were interspersed with more humid intervals and can be correlated using stratigraphic and geomorphic evidence at the regional level the initial phase of the late pleistocene was characterized by significant loess deposition and the formation of large alluvial fans these sediments and landforms are representative of a dry climate the transition to the late pleistocene was marked by the initiation of a humid climate regime giving rise to enhanced fluvial activity and sedimentation expansion and integration of drainage networks and development of paludal areas and successions pedogenesis occurred in the interbasin areas involving precipitation of silica and sesquioxides during latest pleistocene early holocene time coinciding in part with the last glacial maximum a dry and cool climate resulted in widespread aeolian sand and loess deposition the early to mid holocene was characterized by humid subtropical conditions which became established throughout the region accompanied by pedogenic development of profiles with prominent bt horizons and further modification of drainage networks during the mid to late holocene these warm and humid conditions were replaced by a semiarid climate resulting in widespread aeolian deposition wind action formed deflation hollows and dune fields in several areas the climate reverted to subhumid and temperate conditions during the latter part of the late holocene and small areas of wetlands developed the little ice age was marked by climatic deterioration and the deposition of a thin layer of aeolian sediment the current climate of cordoba is subhumid and temperate

pedosedimentary development of part of a late quaternary loess palaeosol sequence in northwest argentina the field properties magnetic susceptibility particle size calcium carbonate content soil micromorphology and optical luminescence ages of the upper 6 1 m and lowermost 4 7 m of the 45 m loess palaeosol sequence at el lambedero in the tafi del valle region of tucuman province sierras pampeanas northwest argentina have been used to set up a partial stratigraphy and chronology as well as a basic pedosedimentary model of loess accumulation palaeosol development reworking and erosion for the site the minimum ages derived from the basal part of the section suggest that loess began to accumulate some time before 165 ka a thick and well developed pedocomplex in the upper profile is correlated with at least the latter part of marine isotope stage mis 5 whereas the overlying palaeosol may be attributable to pedogenic activity during mis 3 the absence of material younger than 33 ka close to the surface of this rounded spur landform is probably the result of either non deposition or erosional stripping in response to climatic change or episodic uplift in this seismically active region

resistivity structure to a depth of 5 km beneath kilauea volcano hawaii from large loop source electromagnetic measurements 0 04 8 hz a deep resistivity study of kilauea volcano using the controlled source electromagnetic csem technique has revealed that the summit region i e the area bounded by the east rift zone the southwest rift zone and the koa e fault zone consists of subhorizontal layers having resistivities ranging from 2 ohm m to greater than several hundred ohm meters the vertical sequence of resistivities is consistent with an increase in temperature from 20 c at the surface to over 1000 c at a depth of about 5 km temperatures beneath the adjacent but inactive area of mauna loa probably do not exceed 300 c at a comparable depth a deep conductor which is indicated by data at five observation locations on kilauea may be magma the source for the csem study is a horizontal wire square approximately 2 km on a side through which a sinusoidal current of about 80 a peak to peak is driven at frequencies between 0 04 and 8 hz

recent ground movement and seismic activity in campi flegrei southern italy episodic growth of a resurgent dome leveling surveys in campi flegrei an active volcanic caldera in southern italy show that this caldera has undergone both subsidence and uplift of a few meters during the past 85 years a single source located at a depth of about 3 km beneath the center of the caldera can account for almost all elevation changes recorded in campi flegrei since the first leveling survey conducted in 1905 1907 this includes leveling surveys that span periods of subsidence such as between 1905 1907 and 1919 and between january 1985 and october 1986 and periods of rapid uplift between march 1970 and october 1971 and between january 1981 and december 1984 a possible geometry for the source of uplift and subsidence beneath campi flegrei is a rectangular horizontal sheet located at a depth of about 3 km and centered a few hundred meters east of the city of pozzuoli the horizontal dimensions of this sheet are about 1 5 km by 3 0 km the long axis is oriented n70 w this sheet lies adjacent to the most intense area of seismicity that occurred from mid 1983 to december 1984 during an uplift episode this sheet may represent the top of a magma body undergoing internal pressure changes possibly by intrusion of additional magma subsidence is caused by groundwater removal from the water saturated deposits that fill this caldera to a depth of a few kilometers a temporary increase in subsidence rate after an uplift episode is caused by increased rate of groundwater removal from newly fractured regions that lie immediately above the magma body the close proximity of this water saturated region and the magma body makes it impossible to separate the depth to these two sources from the results of leveling surveys two observations indicate that uplift has occurred in the center of campi flegrei for at least the past several thousand years first marine deposits in the center of campi flegrei were uplifted at least 40 m between 4000 and 8000 years ago second continuous seismic profiles of the undersea portion of campi flegrei have identified only one region where rocks are fractured and faulted adjacent to the uplifted marine deposits that surround the point of maximum uplift indicated by recent leveling surveys on the basis of these observations and the historical record of activity we suggest that campi flegrei caldera is in a stage of growing a resurgent dome the present diameter of the resurgent dome is about 4 km and the maximum amount of vertical uplift during the past 10 000 years has probably not exceeded 100 m the episodes of rapid uplift and shallow earthquake swarms during the past 20 years are probably related to the growth of this resurgent dome

influence of temperature on the distribution of stress and displacement in a volcano a numerical approach a previously published geological model and numerical finite element simulation of a basaltic vollano is extended by introducing temperature dependent elastic parameters the geological model is composed of a shield with a central volcanic cone resting on oceanic crust the magma system consists of a 3 km deep upper reservoir from which rises a central column the model of the temperature field inside the volcano is based on geological observations and comprises 1 a hot zone 200 300 m thick around the magma system where temperature drops rapidly by conduction and 2 a cooler zone where temperature gently decreases by convection of circulating fluids the temperature dependent parameters the young modulus e the poisson coefficient v and the coefficient of linear thermal expansion of which the first two show a non linear variation with temperature introduce heterogeneity in the medium three zones with different mechanical behaviour are distinguished in the volcanic edifice shearing and strong deformation processes are prominent next to the magma system in the less rigid hot confined zone radial cracks are likely to be initiated in the central part of the volcano where tiffness increases and finally concentric vertical or outward dipping fissures are associated with horizontal extension towards the surface with cold and stiff matenal and a low state of thermal stress the results are used to propose a revised model of the internal structure of basaltic oceanic intraplate volcanoes

origins of massive type sandstones in braided river systems abstract this study details largely ignored massive type predominantly structureless sandstones preserved within braided fluvial successions of carboniferous to triassic age architectural element analysis reveals that these sediments were deposited within sand dominated perennial systems of low braiding index cross stratified braid bar deposits are interbedded with and laterally equivalent to geometrically distinct largely structureless massive type sandbodies identified as two separate architectural elements channel like smc and sheet like sms sub divisions within these broad categories define six geometric units which are texturally distinct from each other and from the structured sediments of the same lithological unit since massive type sandstone elements have many features in common with the deposits of highly concentrated laminar sediment water flows they are interpreted in terms of similar depositional processes smc elements form elongate channel like features which trend both at high angles to and parallel with the palaeoflow of host fluvial channels the lower bounding surfaces of smc elements may be either erosive or non erosive and describe symmetrical cross sections with margins dipping 250 m parallel and transverse to the fluvial palaeoflow direction established from cross stratified sandstones of adjacent architectural elements the basal surface of sms elements may either be undulose where the sandbodies are termed smsu or erosional where they are termed smse internally smsu elements preserve parallel laminae marginal to basal scours diffuse sweeping laminae isolated cross sets and water escape structures the smsu sediments are compositionally identical to the structured sandstones with which they are associated and are interpreted as the result of deposition from highly concentrated stream flows developed through flooding and entrainment of sandy floodplain material along the basal surface of smse elements scours in excess of 4 5 m are preserved which are elongate both parallel and oblique to fluvial flow these are commonly lined with a mudclast breccia and or massive sandstone with crude laminae developed parallel with the margin in the upper portion of smse elements diffuse dune structures and sweeping laminae are preserved smse units are texturally and compositionally immature with respect to the cross stratified sandstones with which they are associated thus they are believed to be of first cycle origin and are interpreted as the deposits of highly concentrated flows possibly generated by glacial outburst floods or jokulhaups

the evolution of craters and calderas on young seamounts insights from sea marc i and sea beam sonar surveys of a small seamount group near the axis of the east pacific rise at 10 n a northwest trending group of seamounts located just west of the east pacific rise epr axis has been mapped using high resolution sea marc i side scan sonar and sea beam multibeam bathymetry these seamounts have 9 13 km basal diameters and the shapes of the volcanos change from conical domes near the epr axis to truncated cones and larger elliptical truncated cones farther away from the rise axis the detailed resolution of constructional volcanic features on these seamounts and the progressive development of summit depressions craters to large complex calderas and summit plateaus suggest to us a succession of evolutionary stages through which seamounts grow our evolutionary scheme for constructing these volcanos calls for the development of satellite extrusive centers around the base of a growing seamount which serve to drain off magmas and precipitate summit collapse the creation of a summit depression on a seamount will structurally constrain the style of eruptive volcanism to be principally along ring fractures which localize vents around the margin of a crater or caldera the concentration and channelization of volcanic eruptions around the top of the volcano lead to a progradation of the summit area and the establishment of a summit plateau the steep sides of a seamount reflect growth of the summit area out over the upper flanks of the volcano caused by continued eruption of lavas around the margin of the caldera the steep constructional slopes are sites for vigorous mass wasting that shapes and modifies flank terrain as a seamount evolves the crestal topography is the product of many volcanic cycles characterized by filling and subsequent draining of the caldera and expansion of caldera area through progressive collapse and migration of primary magmatic conduits the final phase of volcanism may be a calderafilling episode that builds a rough conical mount over the summit plateau

shallow miocene basaltic magma reservoirs in the bahia de los angeles basin baja california mexico the basement in the bahia de los angeles basin consists of paleozoic metamorphic rocks and cretaceous granitoids the neogene stratigraphy overlying the basement is formed from the base to the top by andesitic lava flows and plugs sandstone and conglomeratic horizons and miocene pyroclastic flow units and basaltic flows basaltic dikes also intrude the whole section to further define its structure a detailed gravimetric survey was conducted across the basin about 1 km north of the sierra las flores in spite of the rough and lineal topography along the foothills of the sierra la libertad we found no evidence for large scale faulting gravity data indicates that the basin has a maximum depth of 120 m in the valle las tinajas and averages 75 m along the gravimetric profile high density bodies below the northern part of the sierra las flores and valle las tinajas are interpreted to be part of basaltic dikes the intrusive body located north of the sierra las flores is 2 5 km wide and its top is about 500 m deep the lava flows of the top of the sierra las flores together with the distribution of basaltic activity north of this sierra suggests that this intrusive body continues for 20 km along a nnw trending strike between the sierras las flores and las animas a 0 5 km wide 300 m thick intrusive body is interpreted at a depth of about 100 m this dike could be part of the basaltic activity of the cerro las tinajas and the small mounds along the foothills of western sierra las animas the observed local normal faulting in the basin is inferred to be mostly associated with the emplacement of the shallow magma reservoirs below las flores and las tinajas

source parameters and three dimensional attenuation structure from the inversion of microearthquake pulse width data qp imaging and inferences on the thermal state of the campi flegrei caldera southern italy the three dimensional p wave attenuation structure of the campi flegrei caldera and the estimate of source parameters for 87 local microearthquakes is obtained by the nonlinear inversion of pulse width and rise time measurements by using the method described by zollo and de lorenzo this issue source radii represent the better resolved parameters with values ranging from 70 m to 230 m the dip and strike angles defining fault orientations are usually affected by larger uncertainties and are well constrained only for 11 events the dip fault is usually confined in the range 30 60 with an average uncertainty of 12 the fault strikes mainly range between 60 and 60 and seem to define preferential directions oriented radially from the symmetry axis of the ground deformation stress drop estimates indicate rather low values 0 01 1 mpa which suggest low strength properties of the incoherent and brittle materials filling the caldera primarily yellow tuffs the three dimensional qp images obtained from the inversion of p pulse durations show two significant low qp anomalies between 0 and 1 km of depth in the north eastern sector and at 2 3 km of depth in the central eastern sector of the caldera the high degree of spatial correlation of the low qp zone and low vs as inferred by aster and meyer 1988 at 0 1 km in depth and other geophysical and geochemical observations suggest that this anomaly can be related to the presence of densely fractured porous and fluid filled rocks in the ne sector of the caldera the deeper low qp anomaly is interpreted as being related to a dominant thermal effect we used the surface and deep borehole temperature measurements available in the area to obtain a local calibration curve to convert qp in temperature at campi flegrei the retrieved t qp map shows a high thermal deep disturbance 450 500 c at depths between 2 and 3 km in the eastern sector of the caldera where the most recent eruptive activity is concentrated the present day temperature field retrieved by qp images has been interpreted by using a three dimensional thermal conduction model assuming an extended heat source initial temperature of 800 c located underneath the attenuation anomalous region the results indicate that the qp inferred temperature field can be related to the heat conduction effect of one or more molten bodies whose top should be at about 4 km depth consistent with recent seismic estimates of the magma chamber top at campi flegrei ferrucci et al 1992 this study suggests that the present thermal state and rock rheology of the inner caldera could be controlled by the cooling of molten bodies that originally intruded at depths of 1 4 1 6 km during one or more recent time of 10 kyr eruptive events

historical climatic extremes as indicators for typical scenarios of holocene climatic periods in the pampean plain abstract the holocene has been marked by two different climatic periods in the pampas one 8 5 3 5 kyr b p characterized by temperatures and precipitation higher than today and the other 3 5 1 4 kyr b p semiarid generating parabolic dunes the humid period produced intense pedogenesis down to 40 lat s and a mobilization of iron oxides to 30 lat s which means tropical climate with temperatures above 20 c and precipitation higher than 2000 mm yr sand deflation and development of parabolic dunes occur under climates with 300 400 mm yr this contribution is based on geological and physical proxies typical weather scenarios of those climates are sporadically reproduced today during extremely humid or dry periods on that basis meteorological parameters of years beyond the thresholds of 2000 and 400 mm yr were processed dry periods were characterized by a large thermal amplitude frosts and stronger winds reproducing the continental anticyclonic circulation of the late holocene humid extremes were warmer than normal lower thermal amplitude with rains produced by local convection processes typical scenarios with precipitation above 2000 mm yr are 21 c mean temperature ca 1 c higher than the present record 27 c maximal annual temperatures 16 c minimal annual temperatures more than 1 c higher than the present as a consequence thermal amplitude was smaller than today virtually without frosts characteristic parameters of the late holocene were mean annual precipitation ca 350 mm yr 15 c mean temperature 22 c maximal annual temperatures 8 c minimal annual temperatures showing significative shifts in the dry season lower than normal monthly maximal and mean temperatures higher than today the result is a thermal amplitude larger than today probably higher quantity of frosts per year stronger winds and lower relative air humidity in comparison with the humid climate extreme complete the scenario

numerical simulation of unsaturated flow along preferential pathways implications for the use of mass balance calculations for isotope storm hydrograph separation an objective common to many watershed studies is to separate storm hydrographs into two components water that was present in the watershed prior to a storm event soil moisture and groundwater and water which fell on the watershed during the storm to use this approach a number of assumptions must be made including that the composition of water in the soil moisture and groundwater reservoirs are constant and known the objective of this paper is to show that in settings where flow and transport are dominated by preferential pathways for flow steady state mass balance calculations for quantitative hydrograph separation may be in error we present field data from a site where flow and transport are dominated by preferential pathways relict fractures in saprolite of sedimentary rocks which indicate that the 18o content of the water in the unsaturated and shallow saturated zones is not constant over the course of a storm event we use a numerical model to further explore the interactions between the fractures and surrounding matrix both the field data and modeling results indicate that the 18o of the previous storm event s has a strong influence on water in the fractures on the time scale of a storm event only the water in the matrix immediately surrounding the fracture mixes with water in the fracture while the bulk of the matrix is isolated from fracture flow the spatial and temporal heterogeneity of the 18o in the subsurface and the isolation of the most of the matrix water from flow in fractures make the measurement of a singular 18o value for subsurface reservoirs problematic and the assumption of a constant value doubtful since most near surface geologic materials have preferential flow paths we suggest that quantitative hydrograph separation using mass balance techniques is not possible in most situations future field and modeling investigations using the approach outlined here could be designed to explore the important temporal and spatial scales of variability in watersheds and lead to a more quantitative approach to storm hydrograph separation

climatic variations in the argentine plains during the last 18 000 years the last deglacial hemicycle was characterized by a general increase in temperature and precipitation in the region with a few significant departures from this general trend the present ne sw climatic gradient was maintained throughout the entire period except in the upper holocene the following sequence of events is apparent if the present climate is taken as a reference base 1 a 18 000 8500 yr b p arid and cool with aeolian sand ad loess deposition patagonian fauna climatic isolines temperature precipitation etc were located some 750 km northeast of their present positions 2 b 8500 3500 yr b p humid subtropical with brazilian fauna pedogenesis and fluvial dynamics climatic limits migrated about 800 900 km southwest of their former positions 3 c 3500 1000 yr b p dry subtropical aeolian dynamics the normal latitudinal climatic gradient was interrupted by the occurrence of an anticyclonic centre which stabilized the climate over an area of some 1 600 000 km2 4 d 1000 yr b p little ice age climate was similar to the present one over much of the plains but the northeastern extremity was warmer 5 e little ice age climatic deterioration in the southern belt was characterized by generalized aeolian activity and migration of isolines more than 150 km to the northeast in that area 6 f present climate 19th and 20th centuries subtropical humid in the east and dry in the west

magma reservoir subsidence mechanics theoretical summary and application to kilauea volcano hawaii an analytic model has been developed for the prediction of the three dimensional deformation field generated by the withdrawal of magma from a sill like storage compartment during an intrusion or eruption cycle the model is based on the work of berry and sales 1961 1962 and predicts the vertical displacement components over the areal plane model parameters are the depth of burial h the intrusion half width a the intrusion half length b the thickness of the magmatic interior at the moment of melt withdrawal tm and the planform aspect ratio a b the products of the model include areal deformation maps systematic variation in model parameters within the context of kilauea volcano hawaii have revealed that circular and elliptical deformation patterns result from the collapse of draining rectilinear intrusions at depth moreover the geometric parameters of a storage compartment may interact in complex ways to produce similar deformation patterns the model has been applied to kilauea volcano for three periods of pronounced summit subsidence 1 1921 1927 bracketing the steamblast eruptive phases of 1924 2 june 1972 to december 1972 and 3 december 1972 to may 1973 application of the model requires the simultaneous optimization of five predicted deformation features with respect to field measurements and the derivative deformation maps 1 the vertical displacement maxima 2 the vertical displacement gradients over the areal plane 3 the lateral extent of the deformation field 4 the aspect ratio of the subsidence pattern and 5 the strike of the major axis of the deformation field the constrained geometries and volumes of the inferred collapsed storage cavities for each period are 1 1921 1927 depth 3 km a 1500 m b 4500 m tm 20 m v 540 106 m3 2 june 1972 to december 1972 depth 3 3 km a 600 m b 2000 m tm 1 m v 4 8 106 m3 and 3 december 1972 to may 1973 depth 2 2 km a 500 m b 1612 m tm 1 m v 3 2 106 m3 for 2 and 3 calculated magmatic thicknesses tm happen to be in the range 3 48 0 15 m of measurements for sill like bodies in deeply dissected hawaiian shield volcanoes the fits obtained between calculated and observed deformation patterns allow quantification of the location overall dimensions orientation and volume of the discrete still molten interior of sill like compartments from which magma is tapped during eruption or intrusion

an increment of volcano collapse kinematics of the 1975 kalapana hawaii earthquake abstract earthquakes on kilauea volcano can be even more hazardous than volcanic eruptions the most recent large earthquake was the 1975 kalapana quake which generated a locally damaging tsunami over 8 m of horizontal surface displacement and 3 m of subsidence at the coast the seismic magnitude estimates for this earthquake range from ms 7 2 to mw 7 7 the complexity of the seismic data is matched by the complex surface deformation that was observed with a combination of leveling tilt and electronic distance measurements edm the geodetic data shows evidence of collapse of the caldera due to magma withdrawal localized subsidence over the rift zone normal faulting associated with shallow slumping along the hilina pali and displacement on the basal detachment fault we model the summit caldera rift zones and basal detachment fault as dislocations in an elastic half space to better quantify the sources of deformation related to this devastating event using inversion techniques that allow us to let the data constrain the geometry and magnitude of these sources we find 0 04 km3 of magma withdrawal at the summit between 3 5 m of opening along the rift zone and 7 1 m of slip along the basal detachment at 8 3 km depth models that allow for finer spatial resolution of slip on the detachment show that the largest slip occurred west of the seismically recorded earthquake hypocenter along the region of the fault below the coast and that the majority of the fault slip occurred south of the region of microseismicity our best fitting model has a geodetic moment of 4 1 1020 nm mw 7 7 which is consistent with tsunami models and recent analysis of long period seismic data the residual displacements of sites located in the hanging wall of the hilina pali slump system which were not used in the inversion of the other sources suggest that triggered shallow slumping contributed several meters of horizontal displacement to the coseismic displacement at these sites

modelling gravity variations consistent with ground deformation in the campi flegrei caldera italy abstract in recent years 1970 72 and 1982 84 two inflation episodes took place in the campi flegrei caldera italy characterized by significant ground uplift and gravity variations an elastic half space model with vertical density stratification is employed to compute the displacement field and the gravity variations produced by the deformation of buried layers following the inflation of a spherically symmetric deformation source contributions to gravity variations are produced by dilation contraction of the medium by the displacements of density interfaces the free surface and subsurface layers and of source boundaries and possibly by new mass input from remote distances into the source volume three cases were examined in detail in case i the magma chamber is identified as the deformation source and volume and pressure increase in the magma chamber is due to input of new magma from remote distances in case ii deformation is due to magma differentiation within the magma chamber deformation source with constant mass in case iii the geothermal system is identified as the deformation source and a pressure increase possibly driven by the exsolution of high temperature and high pressure volatiles in the magma chamber is assumed to play a dominant role from the comparison between measured and computed gravity residuals free air corrected gravity variations we can assess that in case i an inflation source with constant density would predict gravity residuals compatible with observations whereas an expansion at constant mass case ii would predict gravity residuals much lower than observed the resolving power of gravity data however prevents accurate assessment of the density of the emplaced material in case iii the pervasive density increase of the geothermal fluids induced by pressure increase is assumed to be the main source of gravity variations the average porosity value required for this model to match both the ground deformation and the gravity residuals is found to be 10 a value which is compatible with measured porosity values at campi flegrei in deep wells the subsidence phases following both inflation episodes and the gravity residuals during subsidence lead us to consider case iii as more plausible even if a suitable combination of cases i and iii cannot be discarded

dynamics of magma storage in the summit reservoir of kilauea volcano hawaii an eruption of kilauea volcano hawaii normally results in a decrease in the internal pressure of a summit magma reservoir as it partly drains the interior of the volcano responses to the decrease in pressure 1 by elastic expansion of remaining magma and gas 2 additional exsolution of gas dissolved in the magma and 3 by contraction of the volcanic edifice this process is modeled here using gravity geodetic and observational data for recent events at kilauea during magma removal the ratio of pressure change in the magma reservoir to the volume of associated summit subsidence ranges from less than 0 22 pa m3 to more than 0 43 pa m3 lower ratios occur during large subsidences because of a large effective volume of the reservoir small events may involve source volumes of only 2 km3 in contrast a volume of near 13 km3 is associated with larger events because the boundary between plastic and elastic behavior may migrate outward with increased time and strain the aggregate compressibility of kilauea s reservoir is significantly increased by volumetric changes of the co2 gas phase by bulk compression and solution with pressure this effect is more pronounced for relatively shallow sources because the bulk modulus of gas is proportional to pressure the average reservoir co2 weight fraction may be near 0 0005 to 0 0009 co2 appears to accumulate in the upper portion of the reservoir where the concentration reaches 0 0030 weight fraction gradual long term subsidences are different from the short term deflations associated with specific eruptions during long term subsidence no net change in mass or pressure occurs within the summit reservoir rifting of the summit area which may tend to shorten the reservoir as it widens or slow degassing and contraction of stored magma may cause long term subsidence

constraining permeabilities in a large scale groundwater system through model calibration abstract the range of field estimates of permeabilities in rocks of the atikokan research area ara canada has been reduced by calibrating a groundwater flow model of the ara the flow model was calibrated to the recharge component of the water balance and to measured freshwater heads in boreholes a good match between field and simulated recharge and between measured and simulated heads was obtained with two different permeability depth distributions that differed by up to two orders of magnitude in places solute transport simulation of the distributions of total dissolved solids tds chlorides cl and oxygen 18 18 o in groundwater in the area was performed to further refine the permeability estimates vertical average linear groundwater velocities from the calibrated flow model were used in one dimensional solute transport models of the system to generate depth concentration profiles of tds cl and 18 o recharge midline and discharge area models of both the fracture zones and the rock mass were employed the midline area is the narrow zone that separates the recharge downward flow area from the discharge upward flow area groundwater flow is essentially horizontal in the midline area envelopes formed by the simulated profiles that were created with the velocities of one simulation case more tightly enclosed the field data tds cl 18 o than those of another simulation case indicating that velocities of the former simulation case better represent the hydrodynamics of the real system the models demonstrate that the scatter of tds cl and 18 o field data for the ara is consistent with the groundwater flow model predictions and can be explained by the complexity arising from different hydraulic regimes recharge midline discharge and hydrogeologic environments fracture zones rock mass of the regional flow system solute transport simulation of hydrochemical constituents can aid in refining and constraining permeabilities in large scale groundwater systems

u s mid atlantic margin structure and early thermal evolution marine seismic experiments have revealed that the u s east coast rifted margin crustal structure is dominated by voluminous volcanics emplaced during continental breakup we present results from seismic data recorded onshore during the 1990 edge mid atlantic onshore offshore seismic experiment that extend the margin crustal profile westward 180 km across the coastal plain and place the offshore results into a broader tectonic context the onshore offshore crustal model defines the crustal thinning profile across the margin enabling calculation of total extension based on direct measurements of crustal thickness we find that the crust beneath the coastal plain is largely unextended has a uniform thickness of 35 km shows no evidence for magmatic additions of sufficient volume to affect seismic velocity and that the total half extension of the crust is 30 to 40 km less than previous estimates by a factor of 3 to 4 we also present results of depth migration of the offshore vertical incidence and wide angle seismic data that yield the most complete and accurate image to date of reflectivity across the u s east coast margin we use this image to analyze margin subsidence by exploiting the stratigraphy of the subaerially extruded basalts beneath the sediments we find that 1 margin subsidence is consistent with a petrogenetic model for initial seafloor spreading magmatism involving high average melting pressures 3 5 4 0 gpa and potential temperatures 1500 c for a present day thermal lid thickness of 225 km 2 it is difficult to explain margin subsidence with a present day lid thickness of much less than 150 km and 3 rapid subsidence following breakup suggests the initially hot mantle underlying the rifting margin cooled very quickly implying a limited and finite initial distribution of hot mantle rather than a continuous upwelling or a ubiquitously warm upper mantle

upper quaternary geology of the lower carcarana basin north pampa argentina abstract the geological evolution of the lower carcarana basin reflects a sequence of dry and humid climates from a geomorphological point of view the area belongs to the pampean eolian system the geomorphological units comprise several fluvial geoforms partially masked by a loess carpet on which eolian erosive forms developed the sedimentary record is not simple the typical profile begins with a predominantly eolian unit composed of silty sand and including two pedogenic levels carcarana fm the formation is the result of the reworking of a dune field in the pampean sand sea is4 it is upper pleistocene in age is 3 another somewhat different climatic deterioration followed related to the begining of the last glacial maximum is 2 which caused the deposition of a loessic mantle tezanos pinto fm subsequent evolution of the climate involved a shift to humid conditions during the hypsithermal period generating a well developed soil at the top of the formation an upper holocene eolian layer san guillermo fm covers the whole sequence at the river margins of the basin the late pleistocene lower holocene eolian deposits are replaced by a complex silty clayey sequence mainly paludal with a soil complex in the middle of the section lucio lopez fm

sill intrusion as a source mechanism of unrest at volcanic calderas the interpretation of dynamic processes that occur in volcanic calderas is not simple the ground deformations and the local seismicity which in other volcanic contexts are usually regarded as precursors to eruption in caldera environment in many cases are not followed by any eruption we formulate a general hypothesis that can explain these behaviors our hypothesis is that the intrusion of a sill can be responsible for the dynamics observed during unrest at calderas in order to investigate the reliability of this hypothesis we developed a dynamic model of sill intrusion in a shallow volcanic environment in our model the sill fed by a deeper magma reservoir intrudes below a horizontal elastic plate representing the overlying rocks and expands with axisymmetric geometry the model is based on the numerical solution of the equation for the elastic plate coupled with a navier stokes equation for simulating the dynamics of the sill intrusion we performed a number of simulations with the objective of showing the main features of the model in the experiments when the feeding process stops the vertical movement reverses its trend and the area of maximum uplift undergoes subsidence under certain conditions the subsidence can occur even during the intrusion of the sill the stress field produced by the intrusion is mainly concentrated in a circular zone that follows the sill intrusion front the features predicted by the model are consistent with many observations carried out on different calderas as reported in the scientific literature

structural and rheological constraints on source depth and overpressure estimates at the campi flegrei caldera italy ingv gruppo nazionale per la vulcanologia ministero dell istruzione universita e ricerca firb project

determination of shear and compressional wave velocity variations and hypocenter locations in a rapidly inflating caldera the campi flegrei during 1982 1985 the campi flegrei caldera underwent a large h 1 7 m rapid hmax 2 mm day 1 and localized radius 6 km uplift p and s arrival times from three component digital seismograms recorded during this period have been used to invert for hypocenter locations and for three dimensional shear and compressional velocity to 3 km first order residual based tomography shows a significant and well resolved high p s ratio anomaly for the volume encompassing the central caldera and the active solfatara crater three dimensional tomographic inversion resolves this central anomaly as a zone of depressed p and s with a high 2 1 p s ratio the three dimensional velocity model and hypocenter distribution are consistent with modeling the central caldera as a zone of nearly water saturated cracks presumably a result of recurrent inflation and deflation in a zone with a shallow water table although the presence of small shallow magma bodies is not precluded

conceptualization of the hydrogeological system of some sedimentary aquifers in savelugu nanton and surrounding areas northern ghana groundwater resources play a pivotal role in the rural water delivery system in ghana the hydrogeological system of middle voltaian terrain was simulated using available data on hydraulic heads and boundary conditions the objective was to characterize the general groundwater flow pattern and provide local estimates of the distribution of hydraulic conductivity and recharge fields the results suggest a predominant ne sw flow direction which ties in with the general regional structural trend and indicates that the hydrogeological conditions of the rocks are controlled by structural entities created in the wake of fracturing and or weathering of the rocks whose primary permeabilities are considerably reduced because of high compaction and low grade metamorphism calibrated hydraulic conductivities range between 1 90 and 10 81 m d the spatial distribution appears to reflect the intensity of fracturing and or weathering of the rock and the proportion of the clay fraction of the weathered zone vertical groundwater recharge has been estimated to range between 0 3 and 4 1 of the annual rainfall this recharge rate is quite low and reflects the imperviousness of the thick overburden because of high clay content in some places and high compaction in others despite this apparently low recharge rate groundwater resources potential in the area appear to be high and increased abstraction from existing abstraction wells by up to 50 does not appear to register significant effects on groundwater budgets at the simulated recharge rates this suggests that the well yields are much lower than the potential of the aquifer system the apparently low yields might be associated with poor well development and the choice of inappropriate well completion materials this study recommends a monitoring system to be developed for a much more regional groundwater flow simulation under transient conditions copyright 2012 john wiley sons ltd

results from new gps and gravity monitoring networks at fernandina and sierra negra volcanoes galapagos 2000 2002 gps and gravity networks were established on sierra negra and fernandina volcanoes in 2000 and remeasured in 2001 and 2002 after a decade in which the caldera inflated by over 2 5 m sierra negra s caldera began to subside between 2000 and 2002 at a rate of about 9 cm a neither inflation nor deflation was accompanied by eruption simple elastic modeling indicates that the deformation at sierra negra can be attributed to volumetric contraction of a 2 1 km deep sill beneath the caldera caused by either movement of magma out of the sill or loss of bubbles through degassing precise gravity measurements support but do not prove the former mechanism fernandina volcano is in a phase of slow refilling of the summit reservoir after the 1995 eruption causing lateral expansion of the caldera rim by about 3 cm a our estimate for the depth of the shallowest part of the fernandina magma chamber is 1 to 2 km neither volcano shows evidence of flank spreading

simulation of groundwater flow within observation boreholes for confined aquifers summary observation wells around a pumping well are the primary means of monitoring the change of hydraulic head in an aquifer pipe flow in open observation boreholes will affect the measurement of hydraulic head in the observation wells and alter the flow patterns around the wells but the influences of non darcian pipe flow in observation wells on the accuracy of hydraulic head measurements are not fully recognized this paper presents a coupled seepage pipe flow theory which integrates the aquifer and well as a continuous medium for assessing the influences the objective of this study is to examine the pipe flow effects in observation wells of varied diameters under several pumping scenarios including different penetration lengths of the pumping well a numerical model based on the galerkin finite element method and the finite difference method was developed for the study numerical simulations were conducted for a homogeneous and isotropic confined aquifer in which a pumping well penetrated a different thickness of the aquifer and a number of full penetrating observation wells were placed to obtain drawdowns the simulation results indicated that vertical pipe flow within the observation wells was significant and the flow was non linear the pipe flow resulted in a conduit effect that disturbed the distribution of the hydraulic head within the observation wells after comparing with the results of the hantush 1961 integral by using the case study which neglected the wellbore effect on the groundwater flow system the authors found that the hantush integral may be only conditionally applicable for estimating the drawdown within the observation wells when well diameter is greater than 0 20 m and radial distance is greater than the thickness of the aquifer our study suggests that use of hydraulic heads from observation wells for the evaluation of groundwater flow systems must be cautious before the pipe flow effect can be assumed to be negligible