natural magnetic disturbance fields not precursors preceding the loma prieta earthquake 1 available records of the magnetic indices dst and ap together with standard observatory recordings of 1 min field levels were examined for the period preceding the earthquake of october 1989 centered near loma prieta california the magnetic records showed that the fraser smith et al 1990 report claiming the existence of a 100 s ultralow frequency geomagnetic field precursor signal at corralitos california foretelling a nearby earthquake is not valid my study shows that the stanford ulf signal was not local but rather widespread throughout the western united states and therefore expected to be due to a coincidental geomagnetic solar terrestrial disturbance field

frequency spectral properties of an ulf electromagnetic signal around the 21 july 1995 m 5 7 yong deng china earthquake abstract the frequency temporal analysis of the electromagnetic field recorded from 30 may 1995 to 24 august 1995 at a site about a hundred kilometer north of the epicenter of the 21 july 1995 yong deng earthquake china has shown a clear systematic variation on an electric dipole in the ultra low frequency range from 0 01 to 0 0005 hz a three fold decrease of the frequency of the maximal energy concentration was observed on 30 may 1995 from 0 005 to 0 0010 hz few hours at the time of the earthquake this decrease was nearly monotonic with superimposed small scale step like fluctuations and continued after the yong deng earthquake for about two weeks when the minimum of 0 001 hz was observed just before its abrupt disappearance the ulf signal is observed on one of the four electric dipoles the instrumentation and the data acquisition system do not generate this signal the signal could be generated by an electrokinetic effect depending on stress field changes in the local environment of one or two probes the results need further understanding and interpretation

late ediacaran magnetostratigraphy of baltica evidence for magnetic field hyperactivity abstract long term changes in characteristics of the geomagnetic field may signal evolutionary changes within the earth s interior among these long term variations the magnetic field reversal rate is probably the best known and most frequently used parameter to evaluate concomitant changes in the earth s core although the reversal rate is well known for the last 150 ma and reasonably constrained back to 300 ma knowledge of the early paleozoic and earlier times is limited hence the haunting question is whether the reversal pattern for the last 300 myr is a good representation of the field behavior over a much longer interval a paleomagnetic study of upper ediacaran sediments from the zigan fm baltica in the western south urals revealed a high temperature dual polarity component that is of primary origin levashova et al 2013 in this paper we present the results of a magnetostratigraphic study from the same sections that can be summed up as follows 1 30 magnetozones are found in the ca 110 meters thick composite section of the zigan fm 2 a similar reversal pattern was reported from upper ediacaran sediments from the white sea coast north russia and sw siberia but has never been found in clastic rocks of any other age 3 the reversal pattern in three remote ediacaran sections could not result from remagnetization or extremely slow sedimentation 4 the reversal rate in the late ediacaran exceeded 20 reversals per million years 5 the field appears to behave in a bipolar fashion during the period of hyperactivity

proving the age of a paleomagnetic pole the case of the ntonya ring structure malawi geological application of paleomagnetic data generally relies on equating radiometric or biostratigraphic age with that of the characteristic remanence yet the standard of proof of paleomagnetic age is often unsatisfactory and is extremely difficult to achieve where contact tests or conglomerate tests are unavailable in this study of the ntonya igneous ring complex the thermoremanent trm origin of one component of natural remanent magnetization nrm is confirmed by paleointensity determination and its carrier is identified mineralogically and the age of this trm is estimated by extrapolation from 40ar 39ar mineral ages the characteristic remanence in the ntonya ring structure which was determined by briden 1968 as d 311 i 43 95 1 9 pole 28 n 15 w is shown to be a trm in single domain pseudo single domain magnetite acquired in a field of approximately half the present geomagnetic field strength the 40ar 39ar mineral ages biotites 471 5 7 ma hornblendes 510 7 ma and the high precision of the paleomagnetic directions combine in a model of steady cooling 4 6 m y 1 that leads us to the conclusion that the thermoremanence was acquired over approximately 13 m y 522 13 m y ago in passing it is shown that the isothermal irm component that dominates the remanence is carried by multidomain magnetite the study shows how remanence age may be determined with precision in the absence of geological constraints it makes the ntonya pole a key point in the african and gondwanan apparent polar wander path correlating with middle cambrian glacial deposits in the sahara at about 80 s paleolatitude

first ediacaran fauna found in western africa and evidence for an early cambrian glaciation ediacara type body fossils are reported here for the first time from the west african craton in algeria this assemblage comprises medusoids comparable to medusinites sp and nimbia a trace fossil and a new genus of body fossil with uncertain affinity the fossils are in sandstones of the neoproterozoic cover separated by a major unconformity from the overlying tillite considered until now to be late neoproterozoic most ediacaran fauna radiated after the varanger ice age and tillites associated in ahaggar with molasse of the pan african belt are overlain by carbonates that were deposited during deglaciation and that locally contain early cambrian shelly fossils therefore we interpret the glaciogenic diamictite as early cambrian in age

magnetic and electric fields associated with changes in high pore pressure in fault zones application to the loma prieta ulf emissions we determined the electric and magnetic fields generated during failure of faults containing sealed compartments with pore pressures ranging from hydrostatic to lithostatic levels exhumed fault studies and strain measurement data limit the possible size of these compartments to less than 1 km in extent rupture of seals between compartments produces rapid pore pressure changes and fluid flow and may create fractures that propagate away from the high pressure compartment along the fault face nonuniform fluid flow results from pressure decrease in the fracture from crack generated dilatancy partial blockage by silica deposition and clearing as pressure increases a direct consequence of this unsteady fluid flow may be associated transient magnetic signals caused by electrokinetic piezomagnetic and magnetohydrodynamic effects models of these processes for fault geometries with 1 km high pressure compartments show that electrokinetic effects are several orders of magnitude larger than the other mechanisms the electrokinetic signals produced by this unsteady flow are comparable in magnitude and frequency to the magnetic signals observed prior to the ml 7 1 loma prieta earthquake of october 18 1989 provided fracture lengths are less than 200 m

detection of ultra low frequency emissions connected with the spitak earthquake and its aftershock activity based on geomagnetic pulsations data at dusheti and vardzia observatories abstract ulf electromagnetic emissions from the spitak armenia earthquake site have been detected observations were carried out at the dusheti and vardzia georgia observatories at distances 120 200 km from the epicentre in a frequency range 0 005 1 hz it is shown that the emission appears several hours before the main shock and some of the powerful aftershocks and is not connected with geomagnetic pulsations of magnetospheric sources

macrofossil and tree ring evidence for a long term forest succession and mid holocene hemlock decline abstract paludified dune fields in southern quebec provided a unique opportunity to analyze a mid holocene forest succession ranging from xero mesophilous forests to treed peatlands which registered the hemlock decline a major biostratigraphic event in eastern north america our fossil tree chronology established from 66 radiocarbon dates of tree stems indicates that white pine and hemlock were present at the study site about 6000 5700 yr b p hemlock reached a maximum 4900 4800 yr b p and then declined between 4600 and 3800 yr b p the species recovered around 3700 yr b p and then decreased when white pine and eastern latch dominated the site after 3000 yr b p and between 2600 and 2200 yr b p respectively tree ring signatures of fossil hemlocks suggest the continuous influence of biotic factors possibly insect defoliators throughout the record as shown by recurrent suppressed growth pattern microscopic examination of the hemlock fossil stems disclosed no evidence of fungal disease the hemlock decline was probably caused by regional posthypsithermal climatic changes toward moister conditions

are all runoff processes the same copyright 2013 john wiley sons ltd introduction research on runoff processes to date has focused on the differences between the main divisions of runoff partitioning indeed our major advancements in runoff theory have come with new differentiations of different forms of overland flow and subsurface stormflow these studies of how runoff processes are different have resulted in our current summaries of runoff regimes conceptually e g the variable source area vsa concept and codified in our models e g topmodel and its derivatives such summaries are captured in iconic figures in textbooks that we teach new generations of hydrologists the most popular of which is shown in figure 1 from dunne 1983 and reproduced more recently in wagener et al 2007 and mirus and loague 2013 although such process differentiation was useful as new dominant forms of runoff were discovered in different climates with different soils slope morphologies and vegetation cover continued differentiation does not appear helpful for improved understanding of runoff dynamics and streamflow generation we seem to have exhausted the main list of runoff classes infiltration excess overland flow saturation excess overland flow and subsurface stormflow some decades ago with perhaps the last wave of minor updates to these processes coming in the 1980s and early 1990s in response to isotope tracing demonstration of the importance of stored water and clarification of differences between hydrologic and hydraulic time scales see reviews by bonell 1993 1998 and in bachmair and weiler 2011 in the spirit of sivapalan 2009 i wonder if it is more useful now to change our organizing question from how are runoff processes different to how are runoff processes similar in many ways i am simply building upon and restating what others have said in recent useful statements on the importance of boundary conditions and flux closures beven 2006 the need for new theory e g troch et al 2008 and new ways of considering runoff systems spence 2010 asking if all runoff processes are the same conceptually is a possible new way to come at runoff process research to aid improved process measurement understanding and prediction through new flexible model structural approaches similar to fenicia et al 2011 across diverse regions it opens up new research questions such as what can we learn about subsurface stormflow from overland flow and vice versa can we recognize things on the surface where boundary conditions are visible that may help guide new theory for the subsurface where such boundary controls are hidden here i present a simple analogical reasoning that shows how all runoff processes are similar this comes following the viewing of many dozens of hillslopes and catchment sites across the world for 25 years especially although i do note that pioneering work in the 1990s in deglaciated landscapes particularly in canada has shown new behaviours outside of these three classes largely linked to groundwater and wetland processes see branfireun and roulet 1998 peters et al 1995 and others

hydrologic effects on water level changes associated with episodic fault creep near parkfield california as part of the parkfield california earthquake prediction experiment water level is monitored in a well 460 m from the main trace of the san andreas fault on middle mountain in the preparation zone of the anticipated parkfield earthquake the well configuration allows water level to be monitored in two fluid reservoirs at depths of 85 and 250 m below land surface during 1987 water level changes were recorded during 12 of the 18 episodes of accelerated fault creep detected by a creep meter spanning the fault trace 750 m northwest of the well the creep related water level changes in the shallow reservoir have durations of less than 1 day whereas in the deeper reservoir the changes persist for as long as 2 months these data suggest that the transient nature of the water level changes in the shallow interval is due to vertical flow to the water table and is not evidence that creep events propagate past the well phase leads of earth tidal constituents in the water level data from the shallow interval relative to the same constituents in the local volume strain tide support the interpretation of significant flow to the water table at periods of 1 day or less the form of the water level changes in the deep interval is affected by horizontal flow to the well bore this effect can be removed from the water level records using a theoretical response curve constrained by the phases of earth tidal constituents in the deep interval relative to the local volume strain tide for the events where the signal in the shallow interval has been large enough to measure the sizes of the simultaneous water level changes in the two reservoirs are consistent with the same amounts of volume strain occurring at both depths

the baseflow and storm flow hydrology of a precambrian shield headwater peatland a hydrological investigation was conducted in a small headwater peatland located in the experimental lakes area north western ontario canada to determine the subsurface and surface flow paths within the peatland and between the peatland and an adjacent forested upland during baseflow and storm flow conditions distinct zones of groundwater recharge and discharge were observed within the peatland these zones are similar to those found in much larger flow systems even though the peatland was only influenced by local groundwater flow groundwater emerging in seeps and flowing beneath the peatland sustained the surface wetness of the peatland and maintained a constant baseflow the response of the peatland stream to summer rain events was controlled by peatland water table position when the basin was dry and antecedent moisture storage on the uplands when the basin was wet the magnitude and timing of peak runoa during wet conditions were controlled by the degree of hydrological connectivity between the surrounding upland terrain and the peatland 1998 john wiley sons ltd hydrol process vol 12 57 72 1998

the hydrological function of upland swamps in eastern australia the role of geomorphic condition in regulating water storage and discharge abstract temperate highland peat swamps on sandstone thpss are a type of wetland found in low order streams on the plateaus of eastern australia they are sediment and organic matter accumulation zones which combined with a climate of high rainfall and low evaporation function as water storage systems changes to the geomorphic structure of these systems via incision and channelisation can have profound impacts on their hydrological function the aim of this study was to develop an understanding of how changes to the geomorphic structure of these systems alter their hydrological function measured as changes and variability in swamp water table levels and discharge we monitored the water table levels and discharges of three intact and three channelised thpss in the blue mountains between march 2015 and june 2016 we found that water levels in intact swamps were largely stable over the monitoring period water levels rose only in high rainfall events returned quickly to antecedent levels after rain and drawdown during dry periods was not significant in contrast the water table levels in channelised thpss were highly variable water levels rose quickly after almost all rainfall events and declined significantly during dry periods discharge also showed marked differences with the channelised thpss discharging 13 times more water than intact swamps even during dry periods channelised thpss also had flashier storm hydrographs than intact swamps these results have profound implications for the capacity of these swamps to act as water storage reservoirs in the headwaters of catchments and for their ability to maintain base flow to downstream catchments during dry times changes to geomorphic structure and hydrological function also have important implications for a range of other swamp functions such as carbon storage emission and exports contaminant sorption downstream water quality and biodiversity as well as the overall fate of these swamps under a changing climate

the influence of hyporheic exchange on reach scale water budgets in a precambrian shield catchment quebec canada the influence of hyporheic exchange on water and solute budgets of streams is widely identified as important yet there is a notable absence of research identifying its role in precambrian shield headwater streams this research addressed this shortcoming by quantifying the proportions of solute mass loss net and gross water gains and losses for selected reaches over a single summer recession period six conservative tracer injections were performed on nine reaches of a 2 94 km2 catchment in gatineau park quebec canada from july to november 2011 high solute exchange occurred for all reaches despite most showing positive net discharge solute losses in stream reaches typically exceeded 10 and substantial gross water losses and gains indicate a high degree of bi directional water exchange along stream reaches both solute loss and the fraction of channel water involved in hyporheic exchange increased throughout the summer in response to a decrease in discharge and increase in the time of contact results support the assertion that reductions in groundwater contributions to streamflow throughout the summer baseflow period allow for greater exchange of water through hyporheic flowpaths which constitute the majority of gross channel losses and gains spatial inter reach variability in mass loss has been previously ascribed to watershed control on exchange potential in this catchment net discharge and gross hydrologic gains were inversely related to the average flowpath gradients within the valley bottom and local hillslope contributing areas copyright 2013 john wiley sons ltd

the metamorphic history of the damara orogen based on k ar data of detrital white micas from the nama group namibia abstract detrital white micas from molasse sediments of the nama group were dated by the k ar method the kuibis subgroup and the underlying pre damara sinclair sequence contain detrital muscovite with ages of 1100 1000 ma and thus cannot be derived from the damara orogen but prove to have originated from a basement probably affected by the kibaran orogeny muscovite size fractions of 250 100 m from the upper nama group upper schwarzrand and fish river subgroups yielded k ar ages 670 570 ma because these sediments are regarded as molasse series of the damara orogen these k ar ages can be interpreted as cooling ages of a first early tectono thermal event in the damara orogen a later damaran metamorphic overprint which peaked at about 530 ma is not documented in the detrital content of the nama group at the present level of erosion because detrital micas with k ar ages over 600 ma have been found up to the uppermost fish river subgroup it can be concluded that at least two tectono metamorphic events followed by uplift and erosion have taken place during the development of the damara orogen thermal alterations of the nama sediments were detected by means of illite crystallinity and k ar dating of clay size fractions these data as well as the almost exclusive occurrence of the 2m mica polytype in these size fractions point to a diagenetic to very low grade metamorphic alteration of the area investigated at about 530 500 ma and younger the deposition of the upper nama group is younger than the 570 ma detrital white micas but occurred before the 530 500 ma thermal alteration of the nama deposits the deposition of the lower nama group probably took place between 635 and 570 ma

palaeomagnetism of neoproterozoic glacial rocks of the huabei shield the north china block in gondwana abstract a palaeomagnetic study is reported of reddened facies fengtai formation of neoproterozoic glacial rocks which underlie early cambrian rocks with disconformity in the huabei north china sino korean block the diamictite preferred age 620 600 ma carries a dual polarity remanence residing in hematite of the red matrix the mean direction derived from 62 samples is d i 205 9 32 4 95 3 9 yielding a pole position at 233 e 62 n tests on the matrix deformed beneath dropstones suggest that remanence was fixed before full compaction although clasts near the base of the formation are largely overprinted overlying early cambrian sediments of the houjiashan and yutaishan formations have a similar remanence also of dual polarity d i 205 5 32 1 95 3 9 32 samples the magnetisation in the diamictite is therefore interpreted to have been acquired during loading by the ice sheet and or the overlying cambrian succession red shales from the liulaobei formation 890 840 ma near the base of the neoproterozoic succession in the huabei block yield a contrasting remanence of d i 59 4 75 3 95 7 1 19 samples equivalent to a pole position at 150 e 43 n pole positions from this study accord with lower middle cambrian poles from the australian and south china blocks with north china sited adjacent to northeastern australia in accordance with recent biogeographic and palaeogeographic models although the palaeolatitude derived from the fengtai diamictite 17 is cambrian in age and probably later than the glaciation the correlation with australia implies that glaciation in north china took place in low palaeolatitudes 20 and reinforces the view that late neoproterozoic glaciation at least at this perimeter of gondwana occurred at low latitudes neoproterozoic cambrian poles from north china south china and australia fail to conform to the popular rodinia reconstruction with the latter blocks adjacent to western north america and also fail to support the view that gondwana formed by the fusion of widely separated eastern and western segments during pan african orogeny instead they accord to poles from africa and south america in a precursor of gondwana protogondwana the subsequent palaeozoic derivation of this supercontinent was probably achieved by intracontinental strike slip motion during pan african deformation following extinction of the afro arabian arc

regional aridity in north america during the middle holocene increased aridity throughout the great plains and rocky mountain region during the middle holo cene has been documented from pollen records aeolian proxy variables in lake cores and active sand dune migration varve calibration provided by a continuously varved record of the holocene from a core from elk lake northwestern minnesota shows that the influx of aeolian clastic material increased beginning about 8 ka and ended about 3 8 ka with peak aeolian activity at about 6 ka if aeolian influx to elk lake corresponds in time to aeolian influx in other lakes and to maximum dune activity in minnesota dune fields then the varve calibration in elk lake provides precise time calibration of periods of peak aeolian activity in minnesota palaeowind studies from the minnesota dune fields show that the dominant wind direction when the dunes were active was from the northwest the same as the dominant wind direction in dune fields throughout the great plains and rocky mountains if the mid holocene aeolian act

morphology and origin of the fair oaks dunes in nw indiana usa abstract the fair oaks dunes fod of nw indiana usa is a large 4500 km 2 inland dune field associated with the late wisconsin deglaciation of the laurentide ice sheet meltwaters released by the michigan saginaw and huron erie lobes transported fluvioglacial sediment through the kankakee and tippecanoe valleys and their tributaries the texture and composition of the sand in the fod suggest a saginaw lobe origin of sediment with some huron erie lobe sediment sub mature sand with sub angular grains and a large feldspar content suggests relatively short distance of transport during two or possibly three dune building and dune reworking events we propose a model which explains the development of the dunes in three stages dune development began during the bolling allerod stage 1 15 13 ka interval during this stage anticyclonic easterly and north easterly winds deflated the sand from outwash deposits and built transverse and barchanoid dunes on the western sides of the tippecanoe valley and paleo channels further downwind on the western and southwestern windward margins of the fod loess was deposited during the early younger dryas stage 2 12 5 ka atmospheric circulation changed and westerly winds reworked the original dunes to create a great variety of parabolic dunes simple hemicyclic and lobate parabolic dunes developed in the western fod while further downwind in the eastern and the southern fod more elongated hairpin and windrift dunes developed on the upwind side of the dune field loess deposits remained stable and were not remobilized during the second stage dune development by the early holocene the fod dunes were stabilized until their minor remobilization during the middle holocene stage 3 minor disturbances caused by anthropogenic activities have occurred in last two centuries

paleo oceanographie isotopique des mers post glaciaires du quebec abstract the main hydrological characteristics of the post glacial seas of quebec the gold thwait champlain iberville tyrrell seas and the gulf of laflamme have been investigated by a determination of the isotopic composition 14 c 13 c 18 o of the fauna and sediments of their basins the carbonates are generally depleted in 18 o specially shallow water mollusks which show isotopic compositions as low as pdb 18 o 15 the depletion in heavy isotopes is mainly related to the influx of continental waters particularly glacial meltwater in such basins the isotope geochemistry differs from what is observed in open environments and therefore the standard isotopic paleotemperature technique may not be used directly new data on the isotopic composition of glacial lakes and melting water of the laurentide ice sheet compared with data from present arctic environments have enabled us to calibrate a linear 18 o salinity relationship and to evaluate salinity changes in time and space it is concluded that the present marginal basins of quebec do not show any large differences in either salinity or temperature from the post glacial basins more brackish water has characterized the surficial layers since deglaciation shoaling of the basins due to glacio isostatic rebound later induced local variations in the temperature and salinity the water becoming progressively warmer and more brackish in these basins the geochemistry of carbon is more complex the in situ biological production of co 2 caused large variations in the 13 c content of the carbonates independently of any direct continental influence the observed anomalies in 14 c activity of fossil mollusks are believed to be related to the old water effect and to local influx of dead carbon originating from dissolution by ice meltwater of surrounding carbonate bearing bedrock

chemical dilation and the dual porosity of humified bog peat abstract hydrochloric acid and calcium and sodium chloride salt solutions were passed through humified bog peat cores of 1 m length to determine values for the material properties governing solute transport hydraulic conductivity effective porosity and dispersivity chloride passed through the bulk peat cores about twice as fast as predicted from chloride breakthrough curves measured by selective ion probes inserted into the peat 30 cm downgradient from the source with continued experimentation chloride dispersion increased chloride also passed through the peat up to 12 times slower than predicted by conservative advection the retardation of the chloride fronts the faster bulk transport and the asymmetry of the breakthrough curves all indicate that humified bog peat is a dual porosity medium solutes both move preferentially through active macropore spaces and diffuse into dead pore space in the peat matrix neither the effective porosity nor the dispersivity of the peat could be precisely determined from the breakthrough curves because the hydraulic conductivity and discharge rates through the peat increased as much as five times when the chloride tracer solutions passed through the cores in initial experiments the shapes of the breakthrough curves were generally consistent with dispersivities of the order of centimeters similar to that observed for granular soils at the same length scale meters whereas they flattened considerably during later experiments suggesting dispersivities in the range of tens of centimeters we hypothesize that the interaction of the chloride tracer solutions with organic acid functional groups may cause macropores to dilate and micropores to close off

a pleistocene sand sea on the alaskan arctic coastal plain a ridge and thermokarst basin landscape that is strikingly portrayed in landsat winter imagery consists of large pleistocene dunes that have been modified by younger eolian activity and thermokarst processes this is the most extensive area of large stabilized dunes yet reported in the north american arctic the landscape is of particular interest because it has been proposed as a first order analog for martian fretted terrain recognition of the large dunes permits a new interpretation for linear and curvilinear trends visible in landsat summer imagery

postseismic rebound in fault step overs caused by pore fluid flow near field strain induced by large crustal earthquakes results in changes in pore fluid pressure that dissipate with time and produce surface deformation synthetic aperture radar sar interferometry revealed several centimeters of postseismic uplift in pull apart structures and subsidence in a compressive jog along the landers california 1992 earthquake surface rupture with a relaxation time of 270 45 days such a postseismic rebound may be explained by the transition of the poisson s ratio of the deformed volumes of rock from undrained to drained conditions as pore fluid flow allows pore pressure to return to hydrostatic equilibrium

origin of nama basin bitumen seeps petroleum derived from a permian lacustrine source rock traversing southwestern gondwana abstract biodegraded bitumens associated with quartz and calcite veins in the cambrian fish river subgroup sediments of the nama group of southern namibia have a geochemical signature diagnostic for organic matter that was deposited in a saline lacustrine palaeoenvironment in particular they contain abundant gammacerane carotane and 3 methylhopanes while 24 isopropyl cholestanes and dinosteroids are not detectable sealed tube hydrous pyrolysis of asphaltene and polar fractions yielded saturated hydrocarbons amenable to c isotopic analysis and these analyses show unusually low 13 c values these combined characteristics are also present in immature bitumens from the permian irati formation of brazil and a saline lacustrine facies of the whitehill formation in the karoo basin south africa we conclude that the bitumens originated from whitehill equivalent strata of the kalahari basin deposited in what was an extensive saline lacustrine basin in southwestern gondwana during the early permian in southern africa source rocks of the whitehill formation are generally immature for petroleum generation and it is therefore likely that the nama bitumens were expelled by contact metamorphism during emplacement of karoo dolerite sills and dykes in the jurassic

sequence stratigraphy and sedimentology of the neoproterozoic kuibis and schwarzrand subgroups nama group southwestern namibia abstract the kuibis and schwarzrand subgroups of the nama group form a succession of shallow marine and minor fluvial sedimentary rocks that is exposed over much of central and southern namibia ediacaran type body fossils and the stratigraphic carbon isotope variability indicate a vendian age for much of these strata the precambrian cambrian boundary is in the uppermost part of the schwarzrand subgroup radiometric dating of abundant volcanic ash beds which span much of the vendian and extend into the cambrian part of the section could make the nama group the best calibrated reference section for vendian chronostratigraphy here we describe the sedimentology and sequence stratigraphy of exposures of the kuibis and schwarzrand subgroups in southwestern namibia we place tighter environmental constraints on the paleontology and geochemistry and we identify seven depositional sequences the boundaries of the depositional sequences correspond to the more important disconformities in the kuibis and schwarzrand subgroups their identification is crucial for defining rates of organism evolution and isotopic differentiation

groundwater flow patterns in a large peatland abstract groundwater flow patterns and geochemistry were studied in the mer bleue bog near ottawa ontario canada groundwater flow patterns alternated between recharge i e head gradients producing flow from the surface of the peatland to the deeper peat and discharge i e head gradients indicating flow from the deeper peat towards the surface of the peatland during the summer of 1998 the patterns were controlled by changes in precipitation evapotranspiration and the differential head response of catotelm peat lower layer to changes in water table elevation above average rainfall in the spring created recharge patterns of groundwater flow in the peatland evapotranspiration exceeded precipitation for a three week period in mid summer decreasing head at the water table and reversing flow from recharge to discharge a sustained moisture deficit maintained a flow reversal for 32 days until a 46 mm rainfall raised the water table reversing the vertical hydraulic gradients and restoring recharge flow the mixing of meteoric water and deeper groundwater controls geochemical profiles diffusion modeling shows that the peatland is a long term recharge system however electrical conductivity and cation concentrations in peat pore waters increase up to 60 during a flow reversal and then decrease when recharge conditions are re established the redistribution of substrates from reversed flow is likely important to peatland biogeochemical function

a relationship between dunes fire and climate recorded in the holocene deposits of quebec during the past 5 000 yr bp the tropics have experienced an increase in aridity and aeolian activity in both maritime and continental areas1 4 in contrast the onset and subsequent development of post hypsithermal climates in northern latitudes were primarily conducive to global cooling it is suggested here that aeolian activity in cold environments represents a direct response to this long term cooling trend that began after 6 000 5 000 yr bp at the end of the climatic optimum5 9 this study establishes the holocene chronology of sand dunes near the outer forest limit in northern quebec fig 1 i show here that fires initiate the aeolian activity and that the fire dune relationship is typical of cooling period on this basis a palaeoclimatic reconstruction since the climatic optimum is proposed

sakami moraine quebec a 500 km long moraine without climatic control the laurentide ice sheet in eastern canada disintegrated step by step as evidenced by several morainic complexes although commonly interpreted as reflecting climatic events it seems probable that the disintegration simply related to changes in the dynamics of the ice margin without climatic control from the example of the late glacial sakami moraine in quebec formed during the drainage of lake ojibway into the tyrrell sea the concept of a re equilibration moraine already briefly proposed is developed the construction of such a moraine implies a stabilization of the ice front when the glacier margin previously floating or calving in a lacustrine or marine basin is suddenly grounded because of topographic blocking or abrupt drop of water level due to drainage the glacial retreat then pauses until the equilibrium profile of the ice is restored and a morainic accumulation can form during the halt

anisotropy and depth related heterogeneity of hydraulic conductivity in a bog peat ii modelling the effects on groundwater flow anisotropy and heterogeneity of hydraulic conductivity k are seldom considered in models of mire hydrology we investigated the effect of anisotropy and heterogeneity on groundwater flow in bog peat using a steady state groundwater model in five model simulations four sets of k data were used the first set comprised measured k values from an anisotropic and heterogeneous bog peat these data were aggregated to produce the following simplified data sets an isotropic and heterogeneous distribution of k an isotropic and homogeneous distribution and an anisotropic and homogeneous distribution we demonstrate that where anisotropy and heterogeneity exist groundwater flow in bog peat is complex fine scale variations in k have the potential to influence patterns and rates of groundwater flow however for our data at least it is heterogeneity and not anisotropy that has the greater influence on producing complex patterns of groundwater flow we also demonstrate that patterns and rates of groundwater flow are simplified and reduced when measured k values are aggregated to create a more uniform distribution of k for example when measured k values are aggregated to produce isotropy and homogeneity the rate of modelled seepage is reduced by 28 we also show that when measured k values are used the presence of a drainage ditch can increase seepage through a modelled cross section our work has implications for the accurate interpretation of hydraulic head data obtained from peat soils and also the understanding of the effect of drainage ditches on patterns and rates of groundwater flow

holocene development of parabolic dunes in the central st lawrence lowland quebec abstract stabilized parabolic dunes in the central st lawrence lowland are oriented ne sw in the postulated direction of dune building winds coming from anticyclonic air circulation induced by the retreating laurentide ice sheet about 10 000 yr ago the eolian chronology reconstructed from several sections in mixed dune peatland environments indicates that postglacial plant colonization characterized by a fortuitous assemblage of arctic subarctic and boreal elements preceded dune formation during champlain sea regression around 10 000 yr b p confined peatlands and small forests were buried by eolian sands between 10 000 and 7500 yr b p under dry and temperate conditions this eolian episode lasted about 2500 14 c yr and ended when cyclonic air circulation similar to the present humid climatic regime was established following the breakup and disappearance of the laurentide ice sheet over hudson bay and peripheral areas dune stabilization through paludification of well drained eolian sands about 7500 yr b p suggests a major shift in climate toward wetter conditions that have been characteristic during most of the holocene in eastern north america minor eolian erosion induced by wildfire was recorded during late holocene time about 1250 yr b p anthropogenic perturbation logging and agriculture practice was also responsible for recent very local eolian activity

the neoproterozoic of southwestern africa with emphasis on platform stratigraphy and paleontology abstract neoproterozoic sediments in southwestern africa occur in the pan african kaoko khomas gariep vanrhynsdorp and saldania belts they were deposited in response to rifting break up of a supercontinent formed at 1000 ma and subduction and collisions of the congo kalahari rio de la plata and malvinas plates these collisions led to the formation of a neoproterozoic cambrian supercontinent this paper deals with the geology of the platform successions of the kaoko khomas gariep and vanrhynsdorp belts deposition of the sediments occurring in these belts commenced 900 to 1000 ma ago and probably ended between 500 and 520 ma the sediments record wilson cycles that ended with the deposition of red beds palaeontological and carbon isotope studies on the damara sequence gariep complex nama group and vanrhynsdorp group make intra and inter basinal correlations possible prior to deposition of the nama group two or perhaps three glaciations took place over an extensive area in southwestern africa these being the kaigas chuos 725 700 ma numees 650 600 ma or 610 590 ma and possibly the varianto 745 725 ma glaciations the numees tillite is overlain by a stratigraphic unit containing pinkish dolomite during deposition of the nama group the minor vingerbreek 600 545 ma glaciation or cold water period occurred the major kaigas chuos and numees and minor vingerbreek glaciations correspond with low 13c isotope ratios and appear to have taken place at relatively low palaeolatitudes the riphean sediments were deposited predominantly during rifting and break up of a supercontinent during the late vendian to early cambrian deposition of the nama group in southern namibia and the penecontemporaneous vanrhynsdorp group in the republic of south africa took place in the nama foreland basin detrital micas indicate that deposition of the nama group took place between 635 and 530 ma the nama foreland basin which was connected to a major ocean to the south formed as a result of collisions between the congo kalahari and rio de la plata plates with the exception of the nama group little is known about the palaeontology of the neoproterozoic in southwestern africa the lower nama group is latest proterozoic in age it contains an ediacaran fauna a depauperate assemblage of organic walled microfossils and a relatively well diversified ichnofauna with brooksella diplocraterion and nereites which are atypical of vendian strata many trace fossils are exceptionally small the occurrence of the shelly fossil cloudina and probable calcified metaphytes in the lower nama group suggest that skeletalization in animals and metaphytes occurred almost simultaneously towards the end of the proterozoic the upper nama group is early cambrian in age as indicated by the occurrence of the trace fossil phycodes pedum the upper nama group dominated by red beds contains a low diversity ichnofauna with trace fossils of normal size bio and chemostratigraphy combined with sequence stratigraphy will probably establish how the prominent unconformities which occur in the neoproterozoic of southwestern africa are related to the periods of formation of the wonoka canyons in south australia

co seismic geoelectric potential changes observed in japan co seismic signals of geoelectric potential have been observed for several earthquakes eqs in japan it has been argued that if there are precursory changes stronger signals should be at the time of eq our results prove that co seismic signals do exist but they start with the arrival of seismic waves and not at the origin time of eqs their amplitude does not scale with the dipole length both facts indicate that the changes are local effects of passing seismic waves and not due to electric signals emitted from the seismic source observed changes contain two components oscillatory and offset decay ones the former is synchronized with seismic waves whereas the latter with a rise time of a few seconds and a decay time of 0 1 1 hour is suspected to be related to eq induced subsurface hydrological change in both cases the origin of electric potential variations may be electrokinetic

shallow groundwater surface water interactions in pond peatland complexes along a boreal plains topographic gradient shallow pond peatland complexes are important water resources and waterbird habitat on the boreal plains of canada and are potentially threatened by accelerated resource development we examined two shallow pond peatland complexes located in contrasting topographic positions within a clay rich till region one on a moraine and one on a lowland clay plain to evaluate the influence of landscape position on wetland groundwater surface water interactions hydrologic function and potential response to disturbance hydrometric and geochemical measurements indicated that precipitation and evaporation dominated the annual water balance of both ponds forested mineral uplands adjacent to the pond peatland complexes contributed no runoff inputs small recharge rates 5 mm year 1 from the ponds through low permeable clay to the underlying aquifer were measured at both topographic locations shallow groundwater fluxes to from the pond were controlled by water storage in and exchange with the adjacent riparian peatlands shallow groundwater fluxes may have contributed as much as 23 of inputs and outputs and influenced pond chemistry and permanence shallow groundwater exchange between the pond and adjacent peatlands varied seasonally and differed between the moraine and lowland complex groundwater flow reversals occurred around the entire perimeter of the moraine pond recharge from the moraine pond to the peatland during dry periods was off set by discharge to the pond from the peatland during wet periods in contrast shallow groundwater flow through conditions were observed at the lowland pond for most of the study however during a high rainfall event a groundwater flow reversal within the outflow peatland initiated discharge back into the pond these results suggest that the hydrologic regimes of some pond peatland complexes in clay rich till within the boreal plains will be more sensitive to local scale disturbances that impact flow dynamics and storage of near shore peatlands rather than larger scale disturbances of mineral upland regions

hydrology of subarctic canadian shield soil filled valleys the canadian shield landscape includes bedrock uplands and valleys infilled with soil a site near yellowknife in subarctic canada was studied to elucidate the hydrological behaviour of soil filled valleys a suite of hydrological processes was found to be important in the studied valley including snowmelt and rainfall ground frost development evaporation infiltration lateral inflow from adjacent uplands and surface and subsurface flows valley storage requirements during snowmelt are met by local meltwater infiltration but lateral inflows in the summer are needed to satisfy the storage before runoff can be generated from the valley the valleys perform three functions of collecting vertical and lateral water inputs retaining and losing the water held in storage and transferring water down the valley and generating local outflow unlike channel flows in humid areas runoff from the upper valley has to meet the storage demands of the lower valley segments often causing seepage loss along flow paths to render the flows intermittent a fill and spill runoff system is proposed in which the valley physiography results in a series of segments with varying storage conditions as water is supplied to the valley each segment has to be filled until its storage threshold for runoff is exceeded then subsurface or surface flows will be generated but these flows may be arrested to furnish water to satisfy the storage requirements of the segments downstream such a flow system applies also to other valleys in the shield environment

high resolution electromagnetic imaging of the san andreas fault in central california although there is increasing evidence that fluids may play a significant role in the earthquake rupture process direct observation of fluids in active fault zones remains difficult since the presence of an electrically conducting fluid such as saline pore water strongly influences the overall conductivity of crustal rocks electrical and electromagnetic methods offer great potential for overcoming this difficulty here we present and compare results from high resolution magnetotelluric mt profiles across two segments of the san andreas fault saf which exhibit very different patterns of seismicity parkfield which has regular small earthquakes and creep events and in the carrizo plain where the fault is seismically quiescent and apparently locked in both surveys electric fields were sampled continuously with 100 m long dipoles laid end to end across the fault from 100 to 0 1 hz the data from both profiles are consistent with a two dimensional 2 d fault parallel resistivity model when both transverse electric and magnetic te and tm mode data are included in the interpretation narrow approximately 300 endash 600 m wide zones of low resistivity extending to depths of 2 endash 4 km in the core of the fault are required at both locations however at parkfield the conductance conductivity thickness product of the anomalous region ismore an order of magnitude larger than at carrizo plain suggesting much higher concentrations of fluids for the more seismically active parkfield segment we also image structural differences between the two segments at carrizo plain resistive presumably crystalline rocks are present on both sides of the fault at depths below 3 endash 4 km in particular we clearly image resistive basement extending approximately 10 km or more east of the saf beneath the elkhorn hills and temblor range at parkfield the situation is quite different with a resistive block of salinian granite west of the fault and an electrically conductive presumably fluid rich franciscan complex to the east it is possible that these structural differences control the difference in mechanical behavior of the fault either directly by affecting fault strength or indirectly by controlling fluid supply copyright 1999 american geophysical union less

effect of groundwater abstraction on fen ecosystems summary quantifying the effects of groundwater abstraction on fen ecosystems located in discharge areas can be complicated the water level in fens is close to the terrain surface most of the year and it is controlled by a relatively constant groundwater exfiltration it is difficult to measure the exfiltration fluxes and thus water level data is typically used to evaluate if the ecosystem is affected the paper presents collected data and analysis from a case study where the hydrological effect of groundwater abstraction on rich fens and springs in a danish river valley has been studied the natural hydrological conditions have been monitored intensively since march 2007 in the early spring 2009 two full scale pumping test were conducted in the regional high yield limestone aquifer the evaluation focuses on three isolated fens covering an area of approximately 5000 m 2 each and two natural springs all within a distance of 1 5 km to a planned well field in the river valley the interaction between groundwater and surface water is strongly affected by low permeable sediments these sediments reduce the direct discharge to the river and have a large impact on the functioning and presence of the rich fen and spring habitats continuous water level data from deep and shallow wells in the fens reflect the hydrological conditions large differences in water level drawdown during dry summer periods have been observed in the monitored fens and it is hypothesised that these differences are directly related to the groundwater seepage rate two pumping tests with duration of 3 weeks were performed at two different locations and the effects were monitored with 20 pressure transducers in monitoring wells and by continuous flow logging in springs in the area a significant reduction of the flow in the springs has been measured while the on the water level in the fens is difficult to distinguish from the natural variations it is concluded that hydrological modelling is a necessary tool in order to predict the long term effects of pumping in the fen areas the collected data gives valuable knowledge on the hydrology of the monitored ecosystems and the response towards groundwater abstraction and forms a solid foundation for hydrological modelling

eolian deflation by ancient katabatic winds a late quaternary example from the north alaska range strong katabatic winds are frequently generated in glaciated mountain valleys of the alaska range by downglacier gravitational flow of chilled air stronger katabatic winds probably occurred during late quaternary time when glaciers were more extensive and such winds may have greatly influenced eolian sedimentation in nenana river valley and in most of adjacent teklanika river valley the entire 1 to 2 m thick eolian cap is postglacial in age and the beginning of loess deposition coincides almost exactly with rapid recession of late wisconsin ice previously deposited loess and bluff edge dunes were apparently deflated during the last glaciation between 25 000 and 12 000 yr b p loess deposition in these mountain valleys thus is exclusively an interglacial phenomenon glacial phases are characterized by deflation meteorological modeling of katabatic winds generated during the last glaciation predicts that paleowind velocities greatly exceeded the entrainment thresholds required for eolian deflation when both nenana river and teklanika river valleys are compared theoretical differences in the potential for generating katabatic winds and differences in valley physiography explain why pre holocene loess is preserved in downstream reaches of teklanika river valley and not nenana river valley the presence of strong katabatic winds in mountain valleys beyond former glacier limits has significant implications for late pleistocene paleoecology and archeology

mapped plant macrofossil and pollen records of late quaternary vegetation change in eastern north america abstract macrofossil presence absence maps and isopoll maps in 3000 year intervals show how ranges and abundance maxima for 12 eastern north american tree and shrub taxa picea p glauca p mariana larix laricina abies balsamea tsuga canadensis pinus strobus p resinosa p banksiana betula papyrifera b alleghaniensis b series humiles have changed from the last glacial maximum to the present the macrofossil maps corroborate patterns shown by the isopoll maps and provide spatial detail and taxonomic resolution the macrofossils confirm the inference from pollen data that unglaciated southeastern north america was cooler during the last glacial maximum 18 and 15 ka than simulated by the cohmap experiments with the ncar ccm0 general circulation model the geographic distribution of macrofossil occurrences during the late glacial 12 and 9 ka indicate that migration lag of boreal species did not occur at regional to subcontinental scales and that pollen assemblages lacking modern analogs resulted from climate gradients lacking modern analogs early holocene 9 and 6 ka macrofossil maps show rapid northward expansion of tree species ranges into deglaciated regions the data also show modest contractions of northern range limits of temperate species and expansions of southern range limits of boreal species in response to cooling trends during the late holocene 3 and 0 ka comparison of modern macrofossil maps of nine of these taxa with corresponding range maps confirm that the macrofossils record the geographic ranges accurately comparison of the modern macrofossil maps with maps of tree growing stock volume shows that for some taxa abies tsuga macrofossil occurrences were most frequent in regions of maximum tree abundance comparison of modern isopoll maps with the modern range and growing stock volume maps indicate that in contrast to the macrofossil data the pollen data provide poorer resolution of range limits for most taxa but better indications of abundance maxima and minima within the ranges

electromagnetic precursors to earthquakes in the ulf band a review of observations and mechanisms despite over 2 decades of international and national monitoring of electrical signals with the hope of detecting precursors to earthquakes the scientific community is no closer to understanding why precursors are observed only in some cases laboratory measurements have demonstrated conclusively that self potentials develop owing to fluid flow and that both resistivity and magnetization change when rocks are stressed however field experiments have had much less success many purported observations of low frequency electrical precursors are much larger than expectations based on laboratory results in some cases no precursors occurred prior to earthquakes or precursory signals were reported with no corresponding coseismic signals nonetheless the field experiments are in approximate agreement with laboratory measurements maximum resistivity changes of a few percent have been observed prior to some earthquakes in china but the mechanism causing those changes is still unknown anomalous electric and magnetic fields associated with fluid flow prior to earthquakes may have been observed finally piezomagnetic signals associated with stress release in earthquakes have been documented in measurements of magnetic fields

the october 17 1989 loma prieta california earthquake and its aftershocks geometry of the sequence from high resolution locations hypocenters of the loma prieta sequence form a dipping zone that rises from the mainshock hypocenter and is parallel to the mainshock nodal plane most aftershocks cluster around the perimeter of the zone surrounding a relatively aseismic center which approximates the region of mainshock rupture at its southeastern end the dipping aftershock zone warps into a vertical surface that corresponds to the san andreas fault in the central and northwestern parts of the zone at depths above 10 km the aftershocks define numerous disjoint fault structures the large component of reverse slip observed in this event agrees with a simple model for slip on a dipping plane within a compressional fault bend we do not believe that the loma prieta earthquake occurred on the sargent fault however we are unable to conclude whether it ruptured the principal plate boundary fault or a less frequently active fault

the hydrology and methylmercury dynamics of a precambrian shield headwater peatland a hydrobiogeochemical investigation of a small headwater peatland located in the experimental lakes area northwestern ontario canada examined the surface and subsurface hydrologic pathways and their relation to the movement and spatial variability of methylmercury ch3hg the hydrology of the peatland controls the mass flux of ch3hg to a downstream pond from the terrestrial ecosystems and influences the production and or accumulation of ch3hg in the peatland distinct zones of groundwater recharge and discharge were observed within the peatland and these corresponded to low and high ch3hg concentrations respectively in pore water the magnitude and flux of ch3hg from the peatland was governed by the area of the peatland and surrounding uplands contributing runoff there was a threefold increase in ch3hg concentration as stream base flow passed from the origin of the stream at the hillslope peatland margin to the stream outlet at the peatland lake interface this relative increase in concentration was maintained during storm flow conditions even though the discharge was up to 10 times greater indicating that the peatland is a large source of ch3hg methylmercury laden peat pore water found near the surface of the peatland in areas of groundwater discharge moves to the stream as the water table rises to the peat surface of a total of 12 6 mg ch3hg leaving the peatland during the 112 day study period less than 1 was transported directly by groundwater 41 was transported in stream base flow and the remaining 58 was transported by storm flow however storm flow conditions occurred only 16 of the time indicating the significance of episodic ch3hg flux from headwater catchments on the precambrian shield

postglacial palaeophytogeography of the eastern st lawrence river watershed and the climatic signal of the pollen record abstract pollen analytical studies of the sediments of over 150 lakes and bogs in southern quebec have led to the indentification of a limited number of sequential types or temporal suites of the various pollen assemblages within each of three main stages of the postglacial development of vegetation the non arboreal stage the afforestation stage and the forest stage these sequential types within any of the three stages show distinct geographical and chronological distributions in southern quebec during the last 12 000 yr when compared in a broader geographic context they demonstrate a strong differentiation of the pollen record within and around the great lakes st lawrence river watershed during the last 15 000 yr b p amongst the most striking gradients identified stand the late glacial perichamplainian gradients ca 11 500 10 000 yr b p and the early holocene gradients the former involve seaward and northeastward clines from closed coniferous forests to tundras and the latter northeastward changes in the nature and duration of the afforestation stage the modern pattern of even the broader vegetational gradients in southern quebec was not attained before 3000 yr b p palynological reconstruction of the various regional paleoclimates highlights the interaction of local regional and global climatic forcings through time mesoscale climate modelling and palaeoclimatology should find boundary conditions in those regional reconstructions

stabilized dune ridges in northern saskatchewan stabilized dune ridges occurring in northern saskatchewan have previously been identified as variedly as ice crack moraines and longitudinal dunes investigations of their morphological structural and sedimentary attributes reveal that they are indeed of eolian origin but they form a particular group within the parabolic dune association namely the cree lake type dune ridges the ridges occur in association with other types of parabolic dunes and other eolian features such as loess and wind abraded glacial blocks and bedrock outcrops the dunes and the associated eolian features were all formed by southeasterly paleowinds of uniform direction the dune ridges developed from primary parabolic dunes of simple and composite types through the process of dune elongation at the same time exposed rock surfaces were abraded by the wind and loess was deposited downwind from the developing dune fields the southeasterly direction of the paleowinds which is almost directly opposite to the direction of

results of ultra low frequency magnetic field measurements during the guam earthquake of 8 august 1993 we report the results of measurements of ultra low frequency magnetic noise during a large earthquake ms 7 1 at guam of 8 august 1993 depth 60 km the ulf observing system is located in the guam island about 65 km from the epicenter several distinct features of this analysis are summarized 1 we have proposed rather sophisticated statistical analyses monthly mean standard deviation in order to estimate the wave intensity and polarization i e ratio z h 2 a comparison between the ulf wave activity and kp is useful in distinguishing between the space geomagnetic pulsations and non space emissions 3 then the use of the ratio z h is found to be of essential importance in discrimating the emissions presumably of seismic origin from space plasma waves 4 the statistical analysis of the temporal evolution of this ratio has yielded that it shows a broad maximum only about one month before the earthquake and this suggests that the emissions during this period are very likely to be magnetic precursors 5 the temporal variation of z component is similar to that for the loma prieta earthquake such that it shows a broad maximum ten days two weeks before the earthquake and another increase a few days before the earthquake 6 the emissions presumably associated with the earthquake are of noise like nature and their main frequency is 0 02 0 05 hz with maximum intensity 0 1 nt

low frequency magnetic field measurements near the epicenter of the ms 7 1 loma prieta earthquake the authors report the results of measurements of low frequency magnetic noise by two independent monitoring systems prior to the occurrence of the m sub s 7 1 loma prieta earthquake of 17 october 1989 their measurements cover 25 narrow frequency bands in the more than six decade frequency range 0 01 hz 32 khz with a time resolution varying from a half hour in the ulf range 0 01 10 hz to one second in the elf vlf range 10 hz 32 khz the ulf system is located near corralitos about 7 km from the epicenter the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf data has revealed no precursor activity that they can identify at this time however the ulf data have some distinctive and anomalous features first a narrow band signal appeared in the range 0 05 0 2 hz around september 12 and persisted until the appearance of the second anomalous feature which consisted of a substantial increase in the noise background starting on 5 october and covering almost the entire frequency range of the ulf system third there was an anomalousmore dip in the noise background in the range 0 2 5 hz starting one day ahead of the earthquake finally and perhaps most compelling there was an increase to an exceptionally high level of activity in the range 0 01 0 5 hz starting approximately three hours before the earthquake there do not appear to have been any magnetic field fluctuations originating in the upper atmosphere that can account for this increase further while the systems are sensitive to motion seismic measurements indicate that there were no significant shocks preceding the quake thus the various anomalous features in the data and in particular the large amplitude increase in activity starting three hours before the quake may have been magnetic precursors less

a systematic compilation of earthquake precursors article a survey of published scientific literature was undertaken to identify and catalog observed earthquake pre cursors the earthquake precursors selected for analysis included electric and magnetic fields gas emissions groundwater level changes temperature changes surface deformations and seismicity for each of these precursors the published scientific literature was searched to document the statistics of each reported earth quake precursor spatial extent time duration amplitude signal noise ratio to analyze dependence of the observable for each precursor on earthquake magnitude and to explore proposed physical models to explain eachearthquakeprecursor somegeneralcharacteristics wereobservedfortheseprecursoryphenomena first the largest amplitude precursory anomalies tend to occur before the largest magnitude earthquakes also the number of precursory anomalies tends to increase the closer in time to the occurrence of the earthquake finally theprecursoryanomaliestendtooccurclosetotheeventualepicenterof theearthquake ingeneral the physical models indicate that all of the precursory phenomena are related to deformation that occurs near the fault prior to the main earthquake while the models provide plausible physical explanations for the pre cursors there are many free parameters in the models that are poorly resolved

groundwater surface water interaction between an esker aquifer and a drained fen summary groundwater discharge from an esker aquifer to a fen was studied to understand relevant hydrological processes for groundwater surface water interaction in an esker peatland hillslope piezometric levels of the peat layer and esker sand layer were continuously monitored and compared to climate data groundwater exfiltration points were spatially mapped and related to peat depth the study showed a clear interaction between fen surface water and sand esker groundwater although the hydraulic conductivity of peat was low and the peat depth thick in the artesian aquifer beneath the fen the piezometric head showed a clear response to precipitation and evapotranspiration wetting of the peat is rapidly seen as pressure increase in the confined aquifer this provides new information on hydraulics of wetlands found in aquifer discharge areas groundwater exfiltrated through thick peat layers in vertical preferential point discharges demonstrating how double porosity provides flow through the peat layer with low hydraulic conductivity in the peat matrix the pipe flow channels were found in the deep peat area in the transition zones from deep peat to shallow peat diffuse seepage through the ditch bottom was found where ditches cut into the sand layer increased discharge through the ditch bed reduced the flow resistance at the aquifer boundary which can lower the groundwater level in the esker the results show new processes in the groundwater discharge zone that are useful for groundwater modelling and policy development for future groundwater protection

simulating vertical flow in large peatlands ground water flow simulations are used to evaluate the importance of three parameters on vertical flow in peatlands regional slope permeability of the mineral soil underlying the peat and peatland topography our results indicate that the extent of vertical ground water flow in peatlands is primarily controlled by mineral soil permeability local ground water flow cells that form under small water table mounds at bog domes can drive peat pore water into permeable mineral soil however when peat forms over low permeability mineral soil vertical movement of peat pore water becomes negligible and lateral flow of water in the upper portion of the peat column dominates the peatland hydrology this effect is not due to the low permeability of humified peat layers as is commonly assumed in many peatland studies field data from the hudson bay lowland canada and the glacial lake agassiz peatlands of northern minnesota confirm the validity of these models these results are relevant in settings other than peatlands where relief is low and small topographic mounds exist

results of ulf magnetic field measurements near the epicenters of the spitak ms 6 9 and loma prieta ms 7 1 earthquakes comparative analysis the characteristics of the ulf magnetic field emissions measured at two magnetic observatories in the republic of georgia prior to and after the ms 6 9 earthquake that occurred near spitak armenia on december 7 1988 are compared with the apparently similar emissions associated with the ms 7 1 earthquake that occurred near loma prieta california on october 17 1989 the main features of the spitak measurements according to observations made at the dusheti station 128 km to the spitak epicenter as compared with the loma prieta measurements which were made at corralitos california 7 km to the loma prieta epicenter are the following 1 the intensity of ulf background activity started growing 3 to 5 days before the spitak earthquake whereas the corresponding increase in activity began 12 days before the loma prieta earthquake 2 a substantial ulf emission burst was recorded at dusheti starting 4 hours prior to the main shock a similar large burst of ulf activity commenced 3 hours before the loma prieta event and continued until the occurrence of the main shock 3 ulf activity remained high for about two weeks after the spitak earthquake and for several months after the loma prieta earthquake 4 ulf noise bursts were observed 1 to 6 hours before powerful aftershocks at spitak during the period of enhanced activity but there was no conclusive link between the ulf noise at corralitos and the after shocks a major difference in the ulf activity preceding the two earthquakes is a difference in amplitude 0 2 nt at spitak and 5 nt at loma prieta but this is easily explained as being caused by the different distances of the observation stations from the epicenters

the identification and biogeochemical interpretation of fossil magnetotactic bacteria magnetotactic bacteria which most commonly live within the oxic anoxic transition zone oatz of aquatic environments produce intracellular crystals of magnetic minerals specifically magnetite or greigite the crystals cause the bacteria to orient themselves passively with respect to the geomagnetic field and thereby facilitate the bacteria s search for optimal conditions within the sharp chemical gradients of the oatz the bacteria may also gain energy from the redox cycling of their crystals because magnetotactic bacteria benefit from their magnetic moments natural selection has promoted the development of traits that increase the efficiency with which the intracellular crystals impart magnetic moments to cells these traits also allow crystals produced by magnetotactic bacteria called magnetofossils when preserved in sediments to be distinguished from abiogenic particles and particles produced as extracellular byproducts of bacterial metabolism magnetofossils are recognizable based on their narrow size and shape distributions distinctive morphologies with blunt crystal edges chain arrangement chemical purity and crystallographic perfection this article presents a scheme for rating magnetofossil robustness based on these traits the magnetofossil record extends robustly to the cretaceous and with lesser certainty to the late archean because magnetotactic bacteria predominantly live in the oatz the abundance and character of their fossils can reflect environmental changes that alter the chemical stratification of sediments and the water column the magnetofossil record therefore provides an underutilized archive of paleoenvironmental information several studies have demonstrated a relationship between magnetofossil abundance and glacial interglacial cycles likely mediated by changes in pore water oxygen levels more speculatively a better developed magnetofossil record might provide constraints on the long term evolution of marine redox stratification more work in modern and ancient settings is necessary to explicate the mechanisms linking the abundance and character of magnetofossils to ancient biogeochemistry

ultra low frequency electromagnetic measurements associated with the 1998 mw 5 1 san juan bautista california earthquake and implications for mechanisms of electromagnetic earthquake precursors abstract ultra low frequency ulf 0 01 10 hz magnetic field anomalies prior to m 6 0 earthquakes have been reported in various regions of the world here we test whether smaller magnitude earthquakes have associated ulf anomalies by using continuous measurements made 9 km above and 2 km ne of the epicenter of the m w 5 1 8 12 98 san juan bautista ca earthquake half hour spectral averages of the magnetic field data in nine different ulf frequency bands show no long term days to weeks magnetic field anomaly prior to the earthquake in addition magnetic and electric field polarization shows no anomalous behavior clearly associated with seismic activity an 0 02 nt increase in activity for 2 h prior to the earthquake is close to the background noise levels precluding identification of a precursor we present scaling calculations to show if precursory ulf anomalies are related to the size of the earthquake the observed 0 02 nt increase is the approximately expected magnetic anomaly prior to the san juan bautista sbj earthquake based on the anomaly observed prior to the 1989 loma prieta lp earthquake our reexamination of previously proposed dilatant conductive and piezomagnetic mechanisms for ulf precursors shows that these effects are consistent with the observations prior to the sjb earthquake based on the observations i e lack of a strong precursor in contrast previously proposed electrokinetic and magnetohydrodynamic mhd mechanisms do not appear to be appropriate for this particular earthquake this analysis further supports the hypothesis that precursory ulf signals are related to the size of the earthquake

analysis of ultralow frequency electromagnetic field measurements associated with the 1999 m 7 1 hector mine california earthquake sequence we installed two electromagnetic em monitoring systems in the im mediate aftermath of the 16 october 1999 hector mine earthquake to search for possible continuing ultralow frequency ulf em activity due to the mainshock as well as for any precursory or coseismic em signals that might be associated with large aftershocks we installed the first portable monitoring system 2 5 days after the m 7 1 hector mine earthquake at a location 16 km southeast of the epicenter and 2 km east of the surface rupture a second system was installed on 29 october 1999 10 km northwest of the epicenter and within 100 m of the surface rupture our continuous measurements of multiple component magnetic field electric field and ground motion span the low frequencies appropriate for recording possible em sig nals generated at seismogenic depths and were carried out during 3 months following the mainshock continuous magnetic field measurements at observatory em stations operating in california are used as remote reference sites to remove global atmo spheric signals which helps isolate local terrestrial sources of interest our analysis of preseismic ulf em variations the coseismic response the 2 month long magnetic field power spectra and electric field polarization shows no anomalous behavior clearly associated with seismic activity

soil water flow dynamics in a managed cutover peat field quebec field and laboratory investigations in this paper concerned with soil water dynamics in a managed cutover peat field the microscale hydrological processes and parameters governing water flow and storage through variably saturated peat are investigated an open water ditch reservoir enhanced wetting of adjacent cutover peat maintaining the water table depth above 43 cm during the summer surface soil moisture above 45 and water tension in the surface layer above 245 mbar desaturation of pores was noted in the 22 and 210 cm depths but at 230 and 250 cm a decrease in moisture content of several percent was associated with compression of the peat as the water table dropped air entry occurred only at pressures below 215 mbar seasonal subsidence resulted in cumulative vertical displacement in excess of 10 cm during the study period typical settlements in the peat ranged between 11 and 23 of the lowering of the water table considerable hysteresis was observed and vertical displacement was 5 times greater in response to water loss compared to rewetting the specific storage s s in the 180 cm thick deposit averaged 9 4 3 10 24 cm 21 during drying periods but averaged only 2 6 3 10 24 cm 21 on rewetting s s was more important than specific yield sy in the overall aquifer storativity transient hydraulic properties resulted from the shifting soil structure the increase in peat bulk density caused by drying increased the water retention capacity and decreased hydraulic conductivity mean saturated hydraulic conductivity was 15 cm d 21 and decreased 2 orders of magnitude as the degree of saturation dropped from 1 to 0 4 the horizontal vertical anisotropy ratio was 4 the changing surface elevation in response to seasonal subsidence had a profound influence on the nature of the storage changes and hydraulic parameters of the peat soil

scaling and physiographic controls on streamflow behaviour on the precambrian shield south central ontario summary relationships explaining streamflow behaviour in terms of drainage basin physiography greatly assist efforts to extrapolate streamflow metrics from gauged to ungauged basins in the same landscape the dorset environmental science centre desc has monitored streamflow from 22 small basins 3 4 190 5 ha on the precambrian shield in south central ontario in some cases since 1976 the basins exhibit regional coherence in their interannual response to precipitation however there is often a poor correlation between streamflow metrics from basins separated by as little as 1 km this study assesses whether inter basin variations in such metrics can be explained in terms of basin scale and physiography several characteristics annual maximum minimum and average flow exhibited simple scaling with basin area while magnitude range and timing of annual maximum daily runoff showed scaling behaviour consistent with the representative elementary area rea concept this rea behaviour is partly attributed to convergence of fractional coverage of the two dominant and hydrologically contrasting land cover types in the desc region with increasing basin size three principal components pcs explained 82 4 of the variation among basin physiographic properties and several runoff metrics magnitude and timing of annual minimum daily runoff mean number of days per year with 0 streamflow exhibited significant relationships with one or more pc significant relationships were obtained between basin quickflow qf production and the pcs on a seasonal and annual basis almost all of which were superior to simple area based relationships basin physiography influenced qf generation via its control on slope runoff water storage and hydrologic connectivity however this role was minimized during spring when qf production in response to large rain on snow events was relatively uniform across the desc basins the pc based relationships and inter seasonal changes in their form were consistent with previous research conducted at point slope and basin scales in the desc region and perceptions of key hydrological processes in these small basins may not have been as readily obtained from scaling studies using streamflow from larger basins this process understanding provides insights into scaling behaviour beyond those derived from simple scaling and rea analyses the physiography of the study area is representative of large portions of the precambrian shield such that basin streamflow behaviour could potentially be extended across much of south central ontario this would assist predictions of streamflow conditions at ungauged locations development and testing of hydrological models for this landscape and interpretation of inter basin and intra annual differences in hydrochemical behaviour on the southern precambrian shield

late pleistocene dune construction in the central sand plain of wisconsin usa wisconsin s central sand plain east of the wisconsin river is composed of eolian sand forming high relief dunes surrounded by sand sheets and scattered low relief dunes to establish a maximum age for dune formation three samples for optical dating were taken from glacial lake wisconsin lacustrine sediment that underlies eolian sand these age estimates range from 19 3 to 13 6ka age estimates taken from within or at the base of the dunes range from 14 0 to 10 6ka samples taken from 2m of the ground surface were slightly younger indicating dunes were stabilized between 11 8 and 5 5ka the younger ages near the surface of some dunes were most likely the result of pedoturbation or localized problems with applying the optical dating method the majority of the optical age estimates from dunes 18 of 21 indicated that most of the dunes were active between 14 and 10ka and that most dune activity ended by 10ka these ages suggest that localized activity on dune crests may have occurred in the holocene but would have been limited to 1m of sand accumulation the timing of dune activity and the lack of any significant holocene reactivation suggest that dune activation in this setting cannot be attributed solely to changes in aridity instead we attribute dune formation to changes in sediment availability from either sand inputs from the wisconsin river or the melting of permafrost

comparison of ultra low frequency electromagnetic signals with aftershock activity during the 1989 loma prieta earthquake sequence abstract ultra low frequency 0 01 to 10 0 hz magnetic field fluctuations near the epicenter of the 1989 loma prieta earthquake rose sharply immediately before the earthquake following indications of increased disturbance during the previous 12 days the magnetic activity remained much higher than the pre earthquake background level for 6 weeks following the mainshock these observations suggest a causal relationship between the earthquake failure process and the magnetic signals a search for similar precursory electromagnetic signals associated with aftershocks of this earthquake yields negative results specifically no correlation appears to exist between the amplitude of the electromagnetic activity and the frequency or magnitude of aftershocks following the mainshock either a threshold earthquake magnitude larger in this case than m l 5 5 may be necessary to generate precursory electromagnetic signals or the continued generation of magnetic signals related to the mainshock may have masked signals generated by the larger aftershocks

the influence of continental ice sheets on the climate of an ice age the climate influence of the land ice that existed 18 000 years before present 18k b p is investigated by use of a general circulation model of the atmosphere coupled with a static mixed layer ocean simulated climates are obtained from two versions of the model one with the land ice distribution of the present and the other with that of 18k b p in the northern hemisphere the tropospheric flow field is strongly influenced by the laurentide ice sheet and features a split flow straddling the ice sheet with a strong jet stream forming the southern branch the northern branch of the flow brings very cold air over the north atlantic ocean where thick sea ice is maintained the distribution of sea surface temperature sst difference between the two experiments in the northern hemisphere resembles the difference between the sst at 18k b p and at present as estimated by the climap project 1981 the 18k b p ice sheets have very little influence upon atmospheric temperature and sst in the southern hemisphere this is because the interhemispheric heat transport hardly changes as the loss of heat energy due to the reflection of solar radiation by continental ice sheets in the northern hemisphere is almost completely counterbalanced by the in situ reduction of upward terrestrial radiation hydrologic changes in the model climate are also found with statistically significant decreases in soil moisture occurring in a zone located to the south of the ice sheets in north america and eurasia these findings are consistent with some geological evidence of regionally drier climates from the last glacial maximum

close temporal correspondence between geomagnetic anomalies and earthquakes during the 2002 2003 eruption of etna volcano 1 the early stages of the 2002 2003 lateral eruption at mount etna were accompanied by slow changes over some hours and some rapid step offsets in the local magnetic field at five monitoring locations the total magnetic field intensity has been measured using continuously operating overhauser magnetometers at a sampling rate of 10 s the very unique aspect of these observations is the close temporal correspondence between magnetic field offsets and earthquakes that occurred in the upper northern flank of the volcano on 27 october 2002 prior to a primary eruption rapid coseismic changes of the magnetic field were clearly identified for three of the most energetic earthquakes which were concentrated along the northeast rift at a depth of about 1 km below sea level coseismic magnetic signals with amplitudes from 0 5 to 2 5 nt have been detected for three of the largest seismic events located roughly midway between the magnetic stations we quantitatively examine possible geophysical mechanisms which could cause the magnetic anomalies the comparison between magnetic data seismicity and surface phenomena implies that piezomagnetic effects are the primary physical mechanism responsible for the observed magnetic anomalies although the detailed cause of the rapid high stress change required is not clear the modeling of the observed coseismic magnetic changes in terms of piezomagnetic mechanism provides further evidence of the complex interaction between volcanic and tectonic processes during dike propagation along the northeast rift

piping and pipeflow in a deep peat catchment abstract natural pipes are common in many upland blanket peats yet little is known about pipe network morphology or pipeflow processes most information on soil piping comes from the shallow peaty podzols of the welsh uplands where monitoring suggests that pipes may be important contributors to streamflow this paper presents information on piping and pipeflow from a deep upland blanket peat catchment in the pennine hills of northern england pipe outlets are found throughout the soil profile ranging from the underlying substrate at 3 m depth to pipes which are within a few centimetres of the surface mean pipe diameters range from 3 to 70 cm some pipes are over 150 m long slopes in the catchment are less steep than those usually associated with soil piping continuous flow records were obtained from 15 gauging sites on 8 separate pipes the pipeflow response from deep blanket peat was found to be different to that reported in the shallow peaty podzols of the welsh uplands the distinction between ephemeral and perennial pipe types does not appear to be useful within the deep pennine blanket peat response times from all of the pipes are short even from pipes deep within the peat at the same time pipes have a prolonged recession limb such that they maintain low flow for longer periods than most other runoff production processes within the catchment pipeflow contributes around 10 of the streamflow volume but can at times contribute up to 30 soil pipes may therefore be far more important in some upland peat catchments than previous work has hitherto suggested

post fire ecohydrological conditions at peatland margins in different hydrogeological settings of the boreal plain in the boreal plain of canada the margins of peatland ecosystems that regulate solute and nutrient fluxes between peatlands and adjacent mineral uplands are prone to deep peat burning whether post fire carbon accumulation is able to offset large carbon losses associated with the deep burning at peatland margins is unknown for this reason we examined how post fire hydrological conditions i e water table depth and periodicity soil tension and surface moisture content and depth of burn were associated with moss recolonization at the peatland margins of three sites we then interpreted these findings using a hydrogeological systems approach given the importance of groundwater in determining conditions in the soil plant atmosphere continuum in peatlands peatland margins dominated by local groundwater flow from adjacent peatland middles were characterized by dynamic hydrological conditions that when coupled with lowered peatland margin surface elevations due to deep burning produced two common hydrological states 1 flooding during wet periods and 2 rapid water table declines during dry periods these dynamic hydrological states were unfavorable to peatland moss recolonization and bryophytes typical of post fire recovery in mineral uplands became established in contrast at a peatland margin where post fire hydrological conditions were moderated by larger scale groundwater flow flooding and rapid water table declines were infrequent and subsequently greater peatland dwelling moss recolonization was observed we argue that peatland margins poorly connected to larger scale groundwater flow are not only prone to deep burning but also lags in post fire moss recovery consequently an associated reduction in post fire peat accumulation may occur and negatively affect the net carbon sink status and ecohydrological and biogeochemical function of these peatlands

hydrology of a headwater basin wetland groundwater discharge and wetland maintenance the link between groundwater and surface hydrology in a small headwater drainage basin in the zone of glacial deposition of southern ontario south of the precambrian shield was examined for two years the basin is situated in a discharge zone of a regional aquifer and contains a small treed spring fed swamp the swamp exists because of the groundwater and has little effect on the maintenance of streamflow groundwater input to the swamp is an order of magnitude larger than precipitation groundwater of local and regional origin passes through the swamp by two routes surface streamlets where groundwater that emerges at specific seepage points in the swamp is conveyed over the ground surface with little interaction with the swamp itself and by diffuse seepage in the swamp and through the bed of the stream while the diffuse seepage input is the smaller component of groundwater it maintains the swamp s saturation groundwater input to the swamp from the specific seepage points and diffuse flow varies little over a year therefore the saturation of the swamp and baseflow from the basin display little seasonal variation compared to other wetland types the existence of the valley bottom in the headwater basin alters the seasonal and storm hydrology and is important to biogeochemical transformation of emerging groundwater

aquifer peatland connectivity in southern quebec canada in areas where peatlands are abundant they are likely to play a significant role in the hydrological and hydrogeological dynamics of a watershed although individual case studies are reported in the literature there is a large range of aquifer peatland interactions and there is a need to understand the controls of these interactions the objectives of this study were 1 to better understand aquifer peatland connections and how these may be predicted by geology and geomorphic location and 2 to provide a variety of reference sites for glacial geological settings slope and depression peatlands were studied in the abitibi temiscamingue region and in the st lawrence lowlands two contrasting regions of southern quebec a total of 12 transects that span a shallow aquifer peatland interface were instrumented with piezometers field investigations included peatland characterization monthly water level monitoring and continuous hydraulic head measurements with pressure transducers the results indicate that 7 of the 12 transects receive groundwater from the surrounding shallow aquifer at the peatland margin four lateral flow patterns were identified and associated with slope peatlands parallel inflow and divergent flow and with depression peatlands convergent flow and parallel outflow vertical hydraulic gradients suggest that water flows mainly downwards i e from the peatland to the underlying mineral deposits vertical connectivity appears to decrease as the distance from the peatland margin increases all of these exchanges are important components in the sustainability of peatland hydrogeological functions the regional comparison of aquifer peatland flow dynamics performed in this study provides a new set of referenced data for the assessment of aquifer peatland connectivity

the nama group revisited summary the nama group of southern namibia is a candidate for the terminal proterozoic global stratotype section and point gssp desirable characteridics of a gssp include a well preserved index fossil assemblage little deformation or metamorphism well constrained isotopic ages stable isotope records and magnetostratigraphic control the age of the nama group sediments is now constrained to between 570 and 510 ma assuming the gondwana assembly was nearly complete at this same time there is a discrepancy between the previously published nama poles a revised 55cl510 ma apparent polar wander path for gondwana and the preceding supercontinental assemblages of rodinia and panottia for these reasons the nama group sediments were resampled in an effort to evaluate the potential of detailing the magnetostratigraphy of the nama group and resolving the discrepancy between the nama poles and the apwp of gondwana collectively both the previous studies of the nama group and this one show a complex series of overprints and no easily discernible primary direction of magnetization we therefore urge caution in using the nama group poles in any tectonic models of the neoproterozoic early palaeozoic specifically the n1 component of magnetization previously identified as a primary magnetization was discovered in a younger suite of samples therefore previous tectonic models that used the n1 magnetization direction as representative of the time of nama deposition should be revised in light of these recent findings

recent movement on the garlock fault as suggested by water level fluctuations in a well in fremont valley california water levels have been continuously recorded since march 1978 in a well in fremont valley where several strands of the adjacent garlock fault zone have exhibited both left lateral displacement and components of normal displacement differences in water levels indicate that a fault segment lies between the observation well and a nearby irrigation well during the 4 year recording period six sharp fluctuations or spikes were noted these fluctuations occurring over 2 to 4 day periods have amplitudes of 15 30 cm they appear to be the result of creep events on a nearby fault two types of creep events are plausible 1 normal slip on an en echelon trace of the garlock fault less than 300 m south of the well with the north side up relative to fremont valley or 2 left lateral slip on the same fault because of the nature of the fluctuations we favor the latter interpretation dislocation models utilizing exponential arc tangent and skewed cosine functions were used to analyze the water level fluctuations associated pressure distribution and fault displacements the results suggest that creep on the fault ranges from several millimeters to a centimeter for individual events estimates of cumulative creep for the period 1978 1982 range from 20 to 50 mm depending on the particular model employed

constraining groundwater discharge in a large watershed integrated isotopic hydraulic and thermal data from the canadian shield or a thin veneer of coarse grained sediments natural conservative d 2 h d 18 o cl and specific conductance radioactive 222 rn and thermal tracers are integrated with streamflow measurements and a steady state advective model to delimit the discharge locations and quantify the discharge fluxes to lakes wetlands creeks and the tay river the groundwater discharge rates to most surface water body types are low indicating that the groundwater and surface water system may be largely decoupled in this watershed compared to watersheds underlain by porous media groundwater discharge is distributed across the watershed rather than localized around lineaments or high density zones of exposed brittle fractures the results improve our understanding of the rate localization and conceptualization of discharge in a large fractured rock watershed applying hydraulic isotopic or chemical hydrograph separation techniques would be difficult because the groundwater discharge signal is small compared to the background surface water inflows or volumes of the surface water bodies although this study focuses on a large watershed underlain by fractured bedrock the methodology developed is transferable to any large regulated or unregulated watershed the low groundwater discharge rates have significant implications for the ecology sustainability and management of large crystalline watersheds

quantification and regionalization of groundwater surface water interaction along an alluvial stream in the present study groundwater seepage to an alluvial stream and two tributary streams was examined at nine field sites using hydrological geophysical and geomorphological observations the data indicate that seepage enters the streams in the following ways i directly through the streambed ii as nearly superficial flow from diffuse discharge areas on the flood plains or iii as a combination of i and ii at about 40 of the sites more than 50 of seepage flows through the streambed moreover it was found that the ratio c defined as the width of the wet zone of the flood plain divided by the effective width of the stream can be used as an indicator of the percentage of water entering the stream directly through the streambed when c is small streambed seepage is large while when c is large streambed seepage is small and ground water enters the stream mainly as nearly superficial or over bank flow from the wet zone

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation

ground penetrating radar and spring formation in a groundwater dominated peat wetland summary ground penetrating radar gpr was used to identify the thickness and geometry of peat in a groundwater fed wetland in northern wisconsin the low electrical conductivity of the water saturated peat permitted high resolution imaging to a depth of 16 m the gpr survey results delineated a break in slope in the interface between peat and the underlying sand gravel springs and ponds are located above the break in slope suggesting that thinning of the sand and gravel may focus groundwater flow upward to the wetland surface with emergence as springs the results of the gpr surveys suggests a potential mechanism that controls the formation of large springs and pools above the break in slope