preferential flow in a sandy vadose zone 2 mechanism and implications abstract field experiments conducted at the hancock agricultural research station during the 1987 growing season showed that preferential flow paths were the dominant flow pattern in the central sand area of wisconsin csaw the observed preferential flow was different from other preferential flow patterns mentioned in the literature e g short circuiting flow and fingering flow this paper presents a detailed discussion of the mechanism of this preferential flow and its influence on groundwater contamination soil solution sampling and solute transport modeling four factors that will determine the occurrence of a funneled flow are a conductivity of the upper finer layer k b slope of the inclined layer sin c retention potential of the upper finer layer 2 r and d ponding potential g l

simulation of preferential flow in three dimensional heterogeneous conductivity fields with realistic internal architecture subsurface flow is primarily controlled by the distribution of hydrogeological properties spatially correlated random fields currently the primary means of describing heterogeneity in these properties underutilizes the existing knowledge of geological systems a new computer code the braided channel simulator bcs 3d is used to geometrically simulate the spatial heterogeneity of hydrogeological properties using representations of surface topography to estimate the three dimensional arrangement of subsurface units four methods of assigning conductivity were used to generate conductivity fields as a basis for saturated flow simulation variograms measured for each of the conductivity fields give no indication of underlying discrete structure however particle tracking simulations showed that flow occurred along paths of preferentially high hydraulic conductivity results indicate that in systems where the contrast in conductivity is sufficiently great the location and magnitude of flow is constrained by discrete internal structure additionally geometrical simulation techniques such as bcs 3d can be used to produce property fields that embody these discrete geological structures

distribution of groundwater seepage to large surface water bodies the effect of hydraulic heterogeneities abstract at 26 sites on the upper great lakes and their connecting channels where groundwater seepage measurements have been made seepages decrease continually offshore at only seven 26 instead 17 63 of the sites have offshore seepages which substantially exceed those at some locations closer to shore the distributions fall into two consistent patterns one where a nearshore decrease in seepage with increasing distance is succeeded offshore by an increase and a second where nearshore seepages are relatively constant and then increase farther offshore the patterns have been observed in two independent studies using two totally different seepage meter designs and emplacement methods and are attributed to hydrogeologic heterogeneities beneath the surface water body detailed marine geophysical measurements at seven sites on green bay show that the anomalously high offshore seepages there are associated with local thinning of the relatively low hydraulic conductivity glacial sediments separating the bay from the underlying aquifer a fractured dolomite at these locations heterogeneity in sediment thickness is a stronger factor in causing seepage anomalies than is heterogeneity of either sediment or bedrock hydraulic conductivity insufficient information exists to confirm a parallel cause effect relation at the other sites but evidence points in that direction similar seepage anomalies have been observed at other smaller lakes by other researchers but never with this frequency it is argued that the cause of the difference is the size of the great lakes seepage occurs and measurements have been made over much greater offshore distances than in smaller lakes and the likelihood that heterogeneities will occur within the zone of measurement is thus also much greater

spatial distribution and budget for submarine groundwater discharge in eckernforde bay western baltic sea submarine groundwater discharge sgd from subseafloor aquifers through muddy sediments was studied in eckernforde bay western baltic sea the fluid discharge was clearly traced by 222 rn enrichment in the water column and by the chloride profiles in pore water at several sites a considerable decrease in chloride to levels less than 10 of bottom water concentrations was observed within the upper few centimeters of sediment studies at 196 sites revealed that 22 of the seafloor of the bay area was affected by freshwater admixture and active fluid venting a maximal discharge rate of 9lm 22 d 21 was computed by modeling pore water profiles based on pore water data the freshwater flow from subseafloor aquifers to eckernforde bay was estimated to range from 4 3 10 6 to 57 3 10 6 m 3 yr 21 therefore 0 3 4 1 of the water volume of the bay is replaced each year owing to negligible surface runoff by rivers sgd is a significant pathway within the hydrological cycle of this coastal zone high resolution bathymetric data and side scan sonar surveys of pockmarks depressions up to 300 m long were obtained by using an autonomous underwater vehicle steep edges with depths increasing by more than 2 m within 8 10 m in lateral directions equivalent to slopes with an angle of as much as 118 were observed the formation of pockmarks within muddy sediments is suggested to be caused by the interaction between sediment fluidization and bottom currents fluid discharge from glacial coastal sediments covered by mud deposits is probably a widespread but easily overlooked pathway affecting the cycle of methane and dissolved constituents to coastal waters of the baltic sea

the co diagenesis of sulfur and iron in acid lake sediments of southwestern quebec reduced inorganic sulfur species constitute the major fraction of total sulfur in the recent sediments of eight acid lakes of southwestern quebec nearly all of the anthropogenically derived excess s present in the sediments has accumulated as reduced inorganic forms showing that organic s formation plays a very minor role in long term anthropogenic s retention in these lakes these results appear different from most other published studies on s fixation in acid lake sediments respectively 74 and 76 of the variance in total s and reduced inorganic s burden in the recent sediments can be explained by their fe content alone indicating that the reduced s is associated with iron and that the capacity of the sediments to retain s may be limited by available fe supply when indexes of organic c supply winter o2 deficit and sediment c are included with fe in a multiple regression analysis respectively 97 and 98 of the variance in total s and reduced inorganic s accumulation can be explained the origin of the pronounced subsurface fe maximum observed in most cores is attributed to the reduction and recent burial as iron sulfides of a surficial diagenetic fe oh 3 reserve in some sediments this fe iii reserve presently appears to be nearly or completely exhausted and the lakes may have lost their capacity to generate permanent alkalinity via so2 4 reduction the present rate of alkalinity production due to so2 4 reduction and fixation of reduced s in the sediments of one lake were estimated from several 210pb dated s profiles and averaged to 163 eq m 2 d 1 this value is comparable to those reported for other acid lakes

resistivity imaging reveals complex pattern of saltwater intrusion along monterey coast abstract electrical resistivity tomography data were acquired along 40 km of the monterey bay coast in central california these data resulted in electrical resistivity images to depths of approximately 280 m b s l which were used to understand the distribution of freshwater and saltwater in the subsurface and factors controlling this distribution the resulting resistivity sections were interpreted in conjunction with existing data sets including well logs seismic reflection data geologic reports hydrologic reports and land use maps from the region interpretation of these data shows a complex pattern of saltwater intrusion resulting from geology pumping and recharge the resistivity profiles were used to identify geological flow conduits and barriers such as palaeo channels and faults localized saltwater intrusion from individual pumping wells infiltration zones of surface fresh and brackish water and regions showing improvements in water quality due to management actions the use of ert data for characterizing the subsurface in this region has led to an understanding of the spatial distribution of freshwater and saltwater at a level of detail unattainable with the previously deployed traditional well based salinity mapping and monitoring techniques alone significant spatial variability in the extent and geometry of intrusion observed in the acquired data highlights the importance of adopting continuous subsurface characterization methods such as this one

pahoehoe and aa in hawaii volumetric flow rate controls the lava structure the historical records of kilauea and mauna loa volcanoes reveal that the rough surfaced variety of basalt lava called aa forms when lava flows at a high volumetric rate 5 10 m3 s and the smooth surfaced variety called pahoehoe forms at a low volumetric rate 5 10 m3 s this relationship is well illustrated by the 1983 1990 and 1969 1974 eruptions of kilauea and the recent eruptions of mauna loa it is also illustrated by the eruptions that produced the remarkable paired flows of mauna loa in which aa formed during an initial short period of high discharge rate associated with high fountaining and was followed by the eruption of pahoehoe over a sustained period at a low discharge rate with little or no fountaining the finest examples of paired lava flows are those of 1859 and 1880 1881 we attribute aa formation to rapid and concentrated flow in open channels there rapid heat loss causes an increase in viscosity to a threshold value that varies depending on the actual flow velocity at which when surface crust is torn by differential flow the underlying lava is unable to move sufficiently fast to heal the tear we attribute pahoehoe formation to the flowage of lava at a low volumetric rate commonly in tubes that minimize heat loss flow units of pahoehoe are small usually 1 m thick move slowly develop a chilled skin and become virtually static before the viscosity has risen to the threshold value we infer that the high discharge rate eruptions that generate aa flows result from the rapid emptying of major or subsidiary magma chambers rapid near surface vesiculation of gas rich magma leads to eruptions with high discharge rates high lava fountains and fast moving channelized flows we also infer that long periods of sustained flow at a low discharge rate which favor pahoehoe result from the development of a free and unimpeded pathway from the deep plumbing system of the volcano and the separation of gases from the magma before eruption achievement of this condition requires one or more episodes of rapid magma excursion through the rift zone to establish a stable magma pathway

uplift and extension at the gulf of suez indications of induced mantle convection reconstruction of tectonic movements since the initiation of the gulf of suez rift indicates that there has been 25 27 km of extension the uplift bordering rift indicates that lithosphere heating greatly exceeds that producible by uniform lithosphere extension i propose that small scale convection induced by the rifting augments the heating introduced by extensional rifting and produces the broad uplifts flanking the rift

geologic influence on groundwater salinity drives large seawater circulation through the continental shelf observations of offshore freshened groundwater and saline groundwater discharge along continental shelves have important implications for water resources ecosystem function and the composition of the ocean but they cannot be explained by basic theory we show that these independent observations are linked and result from processes that drive variable density groundwater flow through the spatial heterogeneity that is ubiquitous in geologic formations we use lithologic data to develop geostatistical models that mimic the architecture of coastal aquifers simulation of groundwater flow and salt transport through these random realizations shows that heterogeneity produces spatially complex subsurface salinity distributions that extend tens of kilometers offshore even at steady state the associated density gradients drive high saline groundwater circulation rates that cannot be predicted by equivalent homogeneous models results suggest that these phenomena may be common along continental shelves potentially altering estimates of ocean chemical budgets and impacting coastal water management for future generations

aerial infrared imaging reveals large nutrient rich groundwater inputs to the ocean 1 regional high resolution 0 1 c 0 5 m low altitude thermal infrared imagery tir reveals the exact input locations and fine scale mixing structure of massive cool groundwaters that discharge into the coastal zone as both diffuse flows and as 30 large point sourced nutrient rich plumes along the dry western half of the large volcanic island of hawaii these inputs are the sole source of new nutrient delivery to coastal waters in this oligotrophic setting water column profiling and nutrient sampling show that the plumes are cold buoyant nutrient rich brackish mixtures of groundwater and seawater by way of example we illustrate in detail one of the larger plumes which discharges ca 12 000 m3 d 1 ca 8 600 m3 d 1 freshwater rates comparable in volume to high flux groundwater outputs in better known tropical karst terrains we further show how nutrient mixing trends may be integrated into tir sea surface temperatures to produce surface water nutrient maps of regional extent

the influence of connected heterogeneity on groundwater flow and salinity distributions in coastal volcanic aquifers abstract geological heterogeneity is a key factor affecting rates and patterns of groundwater flow and the evolution of salinity distributions in coastal aquifers the hydrogeologic systems of volcanic aquifers are characterized by lava flows that can form connected geologic structures in the subsurface surface based geostatistical techniques were adopted to generate geologically realistic statistically equivalent model realizations of a hydrogeologic system based on that of the big island of hawaii conduit models the density dependent groundwater flow and solute transport code seawat was used to perform 3d simulations to investigate subsurface flow and salt transport through these random realizations statistically equivalent geological systems generated with sequential indicator simulation sis and equivalent homogeneous systems were also simulated for comparison simulation results show that conduit realizations tend to have more complex salinity distributions with larger mixing zones for which the center of mass is farther offshore compared to homogeneous and sis realizations the zone of groundwater discharge is also farther offshore than for homogeneous and sis models with higher point fluxes of both fresh and saline water and greater spatial variability this highlights the importance of the geometry of geologic features in coastal groundwater flow and solute transport processes in highly heterogeneous aquifers it also points to the importance of preferential flow with implications for both coastal groundwater resource management and solute fluxes to the ocean

incipient spreading center in the gulf of elat northern red sea abstract the gulf of elat located at the northern red sea is a rift that forms the southern section of the dead sea rift system a recent high resolution seismic reflection survey showed that lenticular grabens and axial anticlines are the predominant structures at the rift floor structural relationships suggest that after the lenticular graben was formed at the rift floor it was filled with sediments axial uplift along the rift caused the widening of the graben and the development of axial anticlines and at a later stage a new graben started to develop between the flank of the anticline and the boundary fault of the rift the data indicate that the tectonic regime affecting the southern dead sea rift is one of uplift and extension acting simultaneously it is presumed that upwelling of magma in the upper mantle extending northwards from the red sea is the cause for these uplift and extensional phenomena and that the gulf of elat is an incipient spreading center

recent sulfur enrichment in the sediments of little rock lake wisconsin multiple sediment cores collected from little rock lake wisconsin prior to experimental acidification show that total sulfur accumulation rates increased during the past century with most of the increase occurring in the nonacid volatile inorganic and organic fractions the increased sulfur accumulation is a result of diagenetic processes within the sediments rather than changes in seston deposition rates or terrestrial inputs this enrichment has occurred because atmospheric sulfate deposition rates have increased over the past century resulting in increased lake water sulfate concentrations which has in turn increased the diffusional flux to the sediments and increased the extent of diagenetic immobilization individual cores had markedly different sulfur accumulation rates demonstrating the importance of collecting multiple cores to determine lakewide sediment accumulation processes that retain sulfate are of considerable interest in the context of lake acidification because they are important in regulating the alkalinity of many soft water present address u s epa environmental research laboratory 200 sw 35th st corvallis oregon 97333 acknowledgments we thank linda shane for contributing to the pollen analysis peter appleby for the gamma spectroscopy analysis and susan christie for editorial assistance the use of the university of wisconsin s trout lake field station is appreciated carol kelly richard holdren and noel urban reviewed an earlier draft of this paper and made numerous suggestions this work was supported through a cooperative agreement between the u s epa and the university of minnesota cr 8 11540 01 lakes see brezonik et al 1987 the magnitude of net sulfate retention as a fraction of input increases with increasing water residence time baker et al 1986 sulfate retention processes can be the dominant source of acid neutralizing capacity anc in seepage lakes with long residence times in the upper midwest and in florida baker et al 1991 sulfate retention can occur by sedimentation by reduction in anoxic hypolimnia or through reactions within the sediment in particular dissimilatory reduction in surficial sediments at sites with oxic overlying water has been recognized as a major sulfate sink kelly and rudd 1984 rudd et al 1986 baker et al 1985 the relative importance of these processes and the extent to which increasing sulfate loadings have resulted in increased mass retention have

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

submarine lava tubes and channels high resolution side looking sonar surveys of the east pacific rise and seamounts in the eastern pacific have revealed the common presence of lava tubes and channels in seafloor volcanic terrains tube and channel systems commonly issue from small volcanic cones or domes are continuous for distances of 1 3 km and are considered to be important in distributing lavas around seafloor extrusive sites and creating characteristic morphology eruption rate and volume are probably the most important controlling factors in determining whether tubes or channels will form volatile content and state slope angle and preeruption surface morphology are secondary factors that influence the ease with which a tube or channel may form and its direction and shape seafloor tubes and channels may also have a profound influence on the structure and evolution of the upper oceanic crust tubes and channels are likely to form intracrustal horizontal pathways for circulating hydrothermal fluids flow differentiation processes acting within tubes and channels may affect the chemical composition of lavas and could be partially responsible for the chemical diversity of rocks along accretionary boundaries seafloor tubes and channels that are either partially water filled or contain volcaniclastics which are then buried within the volcanic pile can lower the compressional velocity and seismic response of the upper oceanic crustal layer along spreading axes

sediment biogeochemistry of iron and sulfur in an acidic lake abstract the biogeochemical cycling of fe and s in the sediments of acidic big moose lake adirondack park ny u s a was investigated sediment cores and porewater samples were collected along a depth transect from the hypolimnion 24 m water depth metalimnion 17 m and epilimion 8 12 m four vertically distinguishable zones in the sediment environment were observed at each site 1 1 no3 disappearance near the sediment water interface 2 2 accumulation of solid phase fe in the top 5 cm 3 3 coincident accumulation of chromium reducible sulfur crs disappearance of so4 and minima in c s and 34s at or slightly below maxima in oxide bound fe and 4 4 homogenous background concentrations in s and fe below 30 and 10 cm respectively iron and sulfur accumulations in the upper 10 cm occurred at the same depths in cores of different ages indicating that diagenetic rather than depositional processes played a dominant role in determining near surface fe and s profiles although sediment accumulation rates varied along the transect the four zones were located at similar depths in the sediment column at all sites diagenetic processes play a major role in the development of these features in big moose lake the extent of fe enrichment was considerably greater in the metalimnetic and epilimnetic sediments in contrast concentrations of fe were lower in hypolimnetic sediments which appeared to be losing fe to the water column at all sites increases in total s from a background concentration of 60 80 mol g 1 of dry mass occurred in sediments dated approximately 1850 more recent increases to 560 mol sg 1 occurred asynchronously in the cores indicating an important role of sulfate reduction in adding s to sediments however organic sulfur accumulation accounted for 22 56 of the recent increase in sediment s concentrations of iron and organic carbon were high in lake sediments and probably do not limit s storage in this lake

hydrogeochemical and isotopic evidence of groundwater salinization in a coastal aquifer a case study in jeju volcanic island korea abstract in order to identify the origin of saline groundwater in the eastern part of jeju volcanic island korea a hydrogeochemical and isotopic study has been carried out for 18 observation wells located in east and southeast coastal regions the total dissolved solid contents of groundwaters are highly variable 77 21 782 mg l oxygen hydrogen sulfur and strontium isotopic data clearly show that the saline water results from mixing of groundwater with seawater strontium isotopic compositions and br cl and i cl ratios strongly suggest that the source of salinity is modern seawater intrusion hydrogeochemical characteristics based on bivariate diagrams of major and minor ions show that changes in the chemical composition of groundwater are mainly controlled by the salinization process followed by cation exchange reactions the highly permeable aquifers at the east coastal region are characterized by low hydraulic gradient and discharge rate and high hydraulic conductivity as compared with other regions these properties enhance the salinization of groundwater observed in the study area based on the cl br and 18 o data seawater was determined to have intruded inland some 2 5 km from the coastline considering the poor correlation of sampling depth and cl concentrations observed the position of seawater freshwater interface is not uniformly distributed in the study area due to heterogeneities of the basaltic aquifers

science society and the coastal groundwater squeeze coastal zones encompass the complex interface between land and sea understanding how water and solutes move within and across this interface is essential for managing resources for society the increasingly dense human occupation of coastal zones disrupts natural groundwater flow patterns and degrades freshwater resources by both overuse and pollution this pressure results in a coastal groundwater squeeze where the thin veneers of potable freshwater are threatened by contaminant sources at the land surface and saline groundwater at depth scientific advances in the field of coastal hydrogeology have enabled responsible management of water resources and protection of important ecosystems to address the problems of the future we must continue to make scientific advances and groundwater hydrology needs to be firmly embedded in integrated coastal zone management this will require interdisciplinary scientific collaboration open communication between scientists and the public and strong partnerships with policymakers

comments on the development of rifts and transform faults during continental breakup examples from the gulf of aden and northern red sea abstract a number of basins are observed to extend inland from the coasts on both sides of the gulf of aden the basins are orientated at approximately right angles to the spreading direction and intersect the coasts at the meeting of sheared and rifted continental margins they appear to be grabens one wall of which is continuous with the half graben of the neighbouring rifted margin it is suggested that these were once parts of a number of discrete rifts arranged en echelon along a zone of lithospheric weakness during the early opening of the gulf of aden which became redundant when transform faults formed the proposed development of rifts and transform faults is similar to that of a spreading centre transform fault spreading centre pattern developed in the freezing wax model of oldenburg and brune 1975 the gulf of suez at the northern end of the red sea is interpreted in a similar way since it has a number of features in common with the basins in the continents adjacent to the gulf of aden

utilizing multichannel electrical resistivity methods to examine the dynamics of the fresh water seawater interface in two hawaiian groundwater systems 1 multichannel electrical resistivity er measurements were conducted at two contrasting coastal sites in hawaii to obtain new information on the spatial scales and dynamics of the fresh water seawater interface and rates of coastal groundwater exchange at kiholo bay located on the dry kona side of the big island and at a site in maunalua bay oahu there is an evidence for abundant submarine groundwater discharge sgd however the hydrologic and geologic controls on coastal groundwater discharge are likely to be different at these two sites while at kiholo bay sgd is predominantly through lava tubes at the maunalua bay site exchange occurs mostly through nearshore submarine springs in order to calculate sgd fluxes it is important to understand the spatial and temporal scales of coastal groundwater exchange from er time series data subsurface salinity distributions were calculated using site specific formation factors a salinity mass balance box model was then used to calculate rates of point source i e spatially discreet and total fresh water discharge from these data mean sgd rates were calculated for kiholo bay 9 200 m3 d and for the maunalua bay site 5 900 m3 d while such results are on the same order of magnitude to geochemical tracer derived sgd rates the er sgd rates provide enhanced details of coastal groundwater exchange that can enable a more cohesive whole watershed perspective

sulfur during early diagenesis in sphagnum peat insights from δ34s ratio profiles in 21pb dated peat cores pb chronologies and depth profiles of stable s isotope ratios 834s and concentrations of organic and inorganic s fractions were determined in peat cores from nine sites in the u s and the czech republic results indicate that depth profiles in s concentrations s accumulation and 634s ratios in peat deposits are affected not only by historical patterns in atmospheric s deposition but also by ongoing depth dependent changes in s reduction oxidation and s immobilization mineralization processes within a peat deposit these processes impart a certain degree of mobility to s in peat bringing into question the validity of reconstructing historical records of s accumulation using dated peat profiles over long term diagenesis isotopically light s may be continually released from deep peat this release may result in redistribution of s and s isotopes in peat and suggests that short term patterns in s accumulation may not persist over much longer time scales

sulfur storage and alkalinity generation in new england lake sediments we measured rates of burial and forms of reduced s in lake sediments to evaluate the importance of so z reduction to the alkalinity budget of several new england lakes the contribution of dissimilatory sod2 reduction to alkalinity generation in these lakes was estimated conservatively to range from 1 to 75 meq m 2 yr l the contribution of both assimilatory and dissimilatory sod2reduction ranged from 10 to 159 meq m 2 yr l for lakes with water residence times on the order of years sod2 reduction can be important in controlling lake water alkalinity we found substantial quantities of inorganic reduced s in sediments of nearly all of the lakes that we studied the majority was present as pyrite in most lakes concentrations of inorganic reduced s were higher in sediments deposited in the last 85 yr when compared to older sediments in contrast the ratio of c to organic s showed no consistent trend with depth in most lakes it appears that in these lakes most of the sulfide produced from s0 2 reduction is stored primarily as inorganic forms rather than as c bonded s in lakes with highly organic sediments and low fe concentrations we found that a considerable portion of the sedimentary fe was present as ferrous sulfides if these lakes were typical alkalinity generation bv reduced s storage in lakes with organic rich sediments in the northeastern u s ilready may be limited by fe availability

constraints on the partitioning of kīlauea s lavas between surface and tube flows estimated from infrared satellite data sulfur dioxide emission rates and field observations this paper describes how observations of sulfur dioxide so2 degassing rates obtained in situ thermal emission rates obtained from infrared satellite data and semiquantitative flow field observations can be used to elucidate the partitioning of lava between the surface and tube systems at k lauea volcano hawai i over a decadal timescale for most of our study period 2000 to 2009 we found that the infrared spectral radiance measured by moderate resolution imaging spectroradiometer from the flow field under clear sky conditions is controlled by the lava effusion rate and the amount of flow accommodated by the subsurface tube system at k lauea the degree of tubing is estimated qualitatively using field observations and we show that the satellite data and in situ gas data can be used to estimate the percentage of lava on the surface relative to the total amount erupted this empirical relationship works to describe many cases in the past decade at k lauea but breaks down when there is a lack of concurrent clear sky radiance and so2 data or when magma is being stored and degassed prior to eruption our observations provide a simple way to estimate the partitioning of k lauea s total lava supply between surface and tube fed flows using a long term dataset this is important because the transition between periods when lava is distributed primarily by surface flows to periods where tubes dominate has been suggested to indicate significant changes in the character of decadal scale eruptions at k lauea heliker et al bull volcanol 59 381 393 1998 in addition it is during those times when surface flows predominate that the flow field does most of its lateral expansion and the hazards associated with the lava effusion become more pronounced

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

the role of paleochannels in groundwater seawater exchange relict fluvial channels that are infilled with high permeability sediments act as preferred pathways for groundwater flow and solute transport in coastal regions such paleochannels can provide a hydraulic connection between freshwater aquifers and the sea facilitating saltwater intrusion landward or freshwater discharge offshore although paleochannels have been implicated in several instances of saltwater intrusion there has been little direct study of these channels to confirm their role in this work simulation modeling of a general multi layered coastal plain aquifer setting indicates that when a paleochannel breaches a confining unit offshore submarine groundwater discharge of intermediate salinity occurs this discharge is largely concentrated along the margins of the channel conversely seawater inflow occurs along the channel axis resulting in higher salinity in the middle of the channel relative to the flanks chirp seismic and electromagnetic data collected offshore wrightsville beach nc usa confirm these simulation results and indicate fresher porewater along channel flanks and slightly higher porewater salinity along the channel axis hence paleochannels contribute to the spatial variability in submarine groundwater discharge by serving as conduits of focused fluid exchange simulations also reveal that the freshwater saltwater transition zone is closer to land below paleochannels than in locations with a continuous confining unit this indicates that such channels are likely to be significant modes of saltwater intrusion into confined aquifers when excess freshwater extraction occurs on land

saltwater intrusion in the unconfined coastal aquifer of ravenna italy a numerical model summary the ravenna pine forests represent an historical landmark in the po river plain they have great environmental historical and tourist value the san vitale pine forest is located 10 km north of the town it is surrounded by an urban area the city industrial infrastructure and the waterworks of the agricultural drainage system most land in this area is below mean sea level as a result no natural freshwater hydraulic gradient contrasts the density gradient of saltwater in the last century many events land subsidence land reclamation and drainage urban and industrial development and gas and deep groundwater extractions coastal dune destruction led to the intrusion of large volumes of brackish and saline groundwater today the freshwater in this coastal aquifer consists of low salinity water lenses floating on the saltwater wedge this study is aimed at understanding how past and present human activities have affected the saltwater intrusion process in the phreatic aquifer and how the predicted future sea level rise will affect the salinisation process we used a numerical model to quantify these effects on the density dependent groundwater flow hydraulic head and salinity distribution seepage and salt load fluxes to the surface water system the simulations show that over the last century artificial subsidence and heavy drainage started the salinisation process in the study area and a relative sea level rise will accelerate the increase in salt load in the coming decades affecting the entire aquifer climatic conditions in the area result in limited precipitations throughout the year and preclude efficient aquifer recharge especially in spring and summer when saltwater seepage is extensive the lack of a continuous coastal dune system favors salt wedge intrusion

large submarine groundwater discharge sgd from a volcanic island 1 we measured seepage rates of coastal groundwater from a volcanic island standing in the south sea of korea the seepage rates measured along the sandy coast were in the range 50 300 m yr which are much higher than those reported from typical continental coast the 18o tracer in potential seeping waters signifies that they are mixtures of basal groundwater and pristine seawaters on the eastern coast of jeju almost all groundwater discharge is attributed to recirculating seawater while fresh groundwater contributes about 20 of the total submarine groundwater discharge sgd on the western coast of jeju thus sgd appears to be important for the management of water resources in western jeju the measured radionuclides 228ra 226ra and 222rn and nutrients in the groundwater suggest that the discharge of both fresh and recirculated seawater will have a significant influence on the budget of coastal nutrients and other chemical constituents in this region

effect of volcanic dykes on coastal groundwater flow and saltwater intrusion a field scale multiphysics approach and parameter evaluation volcanic dykes are common discrete heterogeneities in aquifers however there is a lack of field examples of and methodologies for comprehensive in situ characterization of their properties with respect to groundwater flow and solute transport we have applied an integrated multi physics approach to quantify the effect of dolerite dykes on saltwater intrusion in a coastal sandstone aquifer the approach involved ground geophysical imaging passive magnetics and electrical resistivity tomography well hydraulic testing and tidal propagation analysis which provided constraints on the geometry of the dyke network the subsurface saltwater distribution and the sandstone hydrodynamic properties and connectivity a three dimensional variable density groundwater model coupled with a resistivity model was further calibrated using groundwater and geophysical observations a good agreement of model simulations with tide induced head fluctuations geophysically derived pore water salinities and measured apparent resistivities was obtained when dykes hydraulic conductivity storativity and effective porosity are respectively about three one and one orders of magnitude lower than the host aquifer the presence of the dykes results in barrier like alterations of groundwater flow and saltwater intrusion preferential flowpaths occur parallel to observed dyke orientations freshwater inflows from upland recharge areas concentrate on the land facing side of the dykes and saltwater penetration is higher on their sea facing side this has major implications for managing groundwater resources in dyke intruded aquifers including in coastal and island regions but also provides wider insights on preferential pathways of groundwater flow and transport in highly heterogeneous aquifer systems this article is protected by copyright all rights reserved

heterogeneity induced mixing and reaction hot spots facilitate karst propagation in coastal aquifers the data provided in the included folders are results directly taken from simulations originating from comsol multiphysics all data are provided as text files each text file includes coordinate data and the raw values for the variable of interest presented in the manuscript and supporting information the files provided are separated into folders for homogeneous equivalent cases and heterogeneous cases for each of these folders the data is further subdivided by the variance of the hydraulic conductivity field finally the data is organiyed according to the output variable of interest

on the stability of triple junctions and its relation to episodicity in spreading a convenient representation of triple junctions that involve only ridges r and transform faults f is proposed this representation combines in a simple way information from geographic and velocity spaces the velocity triangle provides the budget of lithospheric surface change which directly results from interactions of the three plates a discussion of the relative positions of the triple junction with respect to the velocity triangle demonstrates that in general there are several triple junction configurations that are compatible with a given triangle this discussion stresses the importance of oblique and asymmetric spreading pairs of triple junction configurations that are of particular interest are rrr rrf and rrr ffr when the triple junction lies outside of the triangle at least one of the ridges will shorten leading to yet another type of potentially unstable configuration the present configurations of the bouvet galapagos and indian ocean triple junctions are reviewed a method is proposed to reconstruct past configurations of the indian ocean junction at the time of anomalies 23 and 28 the main parameters that influence triple junction evolution are the lengths of transform faults the availability of magma and related connectivity of magma chambers and the also related spreading velocities this study confirms an earlier suggestion that activity at constructive plate boundaries occurs in two preferred modes the effusive and tectonic modes corresponding here to rrr and to rrf rff configurations respectively these modes apparently alternate in episodes of typically 1 ma duration the significance of this time constant and consequences for lithospheric mechanics are briefly discussed

preferential rifting of continents a source of displaced terranes lithospheric rifting while prevalent in the continents rarely occurs in oceanic regions to explain this preferential rifting of continents we compare the total strength of different lithospheres by integrating the limits of lithospheric stress with depth comparisons of total strength indicate that continental lithosphere is weaker than oceanic lithosphere by about a factor of 3 also a thickened crust can halve the total strength of normal continental lithosphere because the weakest area acts as a stress guide any rifting close to an ocean continent boundary would prefer a continental pathway this results in the formation of small continental fragments or microplates that once accreted back to a continent during subduction are seen as displaced terranes in addition the large crustal thicknesses associated with suture zones would ironically make such areas likely locations for future rifting episodes this results in the tendency described as the wilson cycle of new oceans to open along the suture where a former ocean had closed

geologic effects on groundwater salinity and discharge into an estuary summary submarine groundwater discharge sgd can be an important pathway for transport of nutrients and contaminants to estuaries a better understanding of the geologic and hydrologic controls on these fluxes is critical for their estimation and management we examined geologic features porewater salinity and sgd rates and patterns at an estuarine study site seismic data showed the existence of paleovalleys infilled with estuarine mud and peat that extend hundreds of meters offshore a low salinity groundwater plume beneath this low permeability fill was mapped with continuous resistivity profiling extensive direct sgd measurements with seepage meters n 551 showed fresh groundwater discharge patterns that correlated well with shallow porewater salinity and the hydrogeophysical framework small scale variability in fresh and saline discharge indicates influence of meter scale geologic heterogeneity while site scale discharge patterns are evidence of the influence of the paleovalley feature beneath the paleovalley fill fresh groundwater flows offshore and mixes with saltwater before discharging along paleovalley flanks on the adjacent drowned interfluve where low permeability fill is absent fresh groundwater discharge is focused at the shoreline shallow saltwater exchange was greatest across sandy sediments and where fresh sgd was low the geologic control of groundwater flowpaths and discharge salinity demonstrated in this work are likely to affect geochemical reactions and the chemical loads delivered by sgd to coastal surface waters because similar processes are likely to exist in other estuaries where drowned paleovalleys commonly cross modern shorelines the existence and implications of complex hydrogeology are important considerations for studies of groundwater fluxes and related management decisions

the tectonics of the timna region in southern israel and the evolution of the dead sea rift abstract the timna region is located in the western margin of the southern arava valley at a junction between two regional orthogonal fault systems the dead sea rift and the temed fault the dead sea rift trends n s and extends from the northern red sea to southern anatolia and the temed fault trends e w from the gulf of suez to the arava valley structural analysis of the timna region showed the effects of two tectonic phases that were active there since the miocene the first tectonic phase formed the dextral strike slip temed fault and two systems of secondary faults trending nw se and ne sw the second tectonic phase downfaulted the rift floor and uplifted the rift shoulders simultaneously forming a regional n s trending joint system along the rift shoulder subsequent sinistral strike slip faulting along the rift caused a drag on the eastern part of the timna region and the resulting 2 5 km northward displacement reactivated pre existing faults and formed several rifts and uplifted blocks a correlation of the structural data of the timna region with recently acquired geophysical structural and stratigraphic findings from various places along the dead sea rift indicates that the first tectonic phase in timna is the erythrean phase this phase formed systems of e w trending faults in the negev and northern sinai as well as nw se trending faults in saudi arabia jordan israel and egypt this tectonic phase was active in the miocene and is associated with the first evolutionary phase of the red sea spreading center during this phase the spreading center extended northwards towards the suez rift the second tectonic phase in timna is the levantine phase that formed the dead sea rift and its uplifted shoulders this phase has been active since the pleistocene and is associated with the second tectonic phase of the red sea spreading the structural and geophysical data suggest that the dead sea rift is an incipient spreading center extending from the red sea whereas the suez rift was not reactivated during this phase the change of trend of the northern red sea spreading center from nw se to n s deformed the east shoulder of the southern dead sea rift so that a limited sinistral strike slip displacement occurred recent seismic activity indicates that the evolution of the dead sea rift is presently active

modes of seawater intrusion during transgressions analytical methods and numerical experiments are used to study salinization of groundwater in response to sea level rise the system that is studied involves a saturated porous medium with an inclined upper surface the upper surface is progressively inundated during sea level rise to simulate transgression the landward migration of the shoreline four modes of seawater intrusion are distinguished 1 horizontal intrusion for slow transgression and a relatively high permeability substrate 2 vertical intrusion by seawater fingering for fast transgression and a sand silt substrate 3 vertical intrusion by diffusion for fast transgression and a low permeability clay substrate 4 vertical intrusion by combined diffusion and low salinity fingering for fast transgression and a clay layer at the seafloor overlying an aquifer these four modes are characterized by the development of very distinctive transition zones between the fresh and salt groundwater domains an analytical expression is derived for the critical transgression rate which separates horizontal mode 1 from dominantly vertical modes 2 4 intrusion for modes 3 and 4 salinization significantly lags behind sea level rise the results are consistent with observations of fossil fresh brackish groundwater beneath many continental shelves and shallow seas

homogenization and effective parameters for the henry problem in heterogeneous formations 1 general upscaling of density dependent flow is investigated for the classical two dimensional henry problem of saltwater intrusion in coastal aquifers combined theoretical and numerical results are here presented effective flow and transport parameters for saline intrusions could be derived for statistically isotropic and anisotropic heterogeneous permeability fields by use of homogenization theory applying also to the preasymptotic regime our numerical results indicate that heterogeneities in permeability affect foremost the transient evolution of saltwater intrusion whereas the steady state saltwater distribution is less sensitive to spatially varying permeabilities and longitudinal dispersion for the isotropic media the effective permeability is found to correspond to the geometric mean as under conditions without fluid density contrast the extension of results to anisotropic media requires nontrivial corrections for the effective permeability which include the variance of log k and the directional correlation lengths the appropriate dispersion coefficients for the problem correspond to the local dispersion coefficients rather than macrodispersion coefficients these results are discussed in light of the specific flow configuration posed in the henry problem

steady state freshwater seawater mixing zone in stratified coastal aquifers summary the mixing zone between freshwater and intruding seawater which controls regional groundwater flow dynamics and reactive transport processes is the most important component in coastal aquifers laboratory experiments and numerical simulations were conducted to investigate the effects of aquifer stratification on the thickness of a steady state freshwater seawater mixing zone a series of experiments were implemented in a laboratory tank packed with three layers of coastal sands and manipulated by two flow cells for maintaining constant head boundary conditions packed aquifers included a homogenous aquifer a high hydraulic conductivity k low k high k stratified aquifer and a low k high k low k stratified aquifer both tank scale and field scale density dependent models were developed to simulate the laboratory experiments and to systematically investigate aquifer stratification effects on the thickness of a steady mixing zone with varying layer configurations results showed that when an aquifer layer with a low k overlies a layer with a relatively high k slanting upward flow of diluted saltwater and re circulated seawater flow are refracted at the interface between the two layers resulting in streamline separation and a broad mixing zone in the low k layer by contrast the mixing zone in a high k layer is slightly narrowed when it overlies a layer with a relatively low k because flow refraction squeezes the streamlines within the mixing zone the mixing zone profile in head controlled systems is a function of k contrast but independent of the magnitude of k our results demonstrated the significant impact of aquifer stratification on controlling groundwater flow and solute transport in coastal subsurface environments and would have significant implications for studying physical chemical and biological processes in coastal subsurface environments as aquifer stratification is naturally prevalent

quantification of point source groundwater discharges to the ocean from the shoreline of the big island hawaii aerial thermal infrared imaging has revealed that submarine groundwater discharge sgd along the western coast of the big island of hawaii is often focused as point source discharges that create buoyant groundwater plumes that mix into the coastal ocean we quantified the sgd fluxes associated with several plumes using natural geochemical tracers offshore transects of 222rn and 224ra show elevated activities and corresponding low salinities in the nearshore waters within the plumes indicating that these naturally occurring radionuclides can be useful tracers of groundwater inputs in this area using a series of simultaneous mass balance equations for water salt and radon we determined the groundwater fluxes of six plumes near kona hawaii the average sgd fluxes ranged from 1100 m3 d21 to 12 000 m3 d21 of total fresh saline sgd the fresh meteoric groundwater equivalents for the same flows modeled by adjusting the groundwater end member to reflect freshwater rather than brackish groundwater composition ranged from 630 m3 d21 to 8600 m3 d21 these fluxes are in general agreement with earlier results obtained by hydrological water budgets and physical oceanographic analyses of fresh sgd rates in this region

a diffuse plate boundary model for indian ocean tectonics it is suggested that motion along the virtually aseismic owen fracture zone is negligible so that arabia and india are contained within a single indo arabian plate divided from the australian plate by a diffuse boundary the boundary is a zone of concentrated seismicity and deformation commonly characterized as intraplate the rotation vector of australia relative to indo arabia is consistent with the seismologically observed 2 cm yr of left lateral strike slip along the ninetyeast ridge north south compression in the central indian ocean and the north south extension near chagos

tectonics of the westernmost gulf of aden and the gulf of tadjoura from submersible observations the gulf of tadjoura separating the danakil and somalia plates1 represents the western extension of the sheba ridge between arabia and somalia in the gulf of aden fig 1 it has been assumed that a simple plate tectonic scheme could be applied to the area with ne sw transform faults offsetting roughly east west zones of accretion represented by the major bathymetrie troughs1 8 fig 1c more recently this boundary has been interpreted as a westward propagating rift with its present day tip on land in the region of the asal lake9 10 here we present data from dives with the submersible cyana which show that there have been two episodes of extensional faulting an older inactive phase parallel to the general ene wsw direction of the gulf and a younger fault set along discontinuous zones striking 140 there is no surface evidence for any transform fault zone in the area covered and the incipient spreading segments whose geometry implies extension on 050 do not define a plate boundary the faulting observed is at odds with that predicted by orthodox plate tectonics

driving mechanisms for groundwater flow and salt transport in a subterranean estuary this paper presents field measurements and numerical simulations of groundwater dynamics in the intertidal zone of a sandy meso tidal beach the study focusing on vertical hydraulic gradients and pore water salinities reveals that tides and waves provide important forcing mechanisms for flow and salt transport in the nearshore aquifer such forcing interacting with the beach morphology enhances the exchange between the aquifer and ocean the spatial and temporal variations of vertical hydraulic gradients demonstrate the complexity and dynamic nature of the processes and the extent of mixing between fresh groundwater and seawater in a subterranean estuary these results provide evidence of a potentially important reaction zone in the nearshore aquifer driven by oceanic oscillations land derived contaminants may undergo important biogeochemical transformations in this zone prior to discharge