dislocation modelling of the 1989 dike intrusion into the flank of mount etna sicily we have applied a dislocation model consisting of a dipping tabular body with constant dislocation perpendicular to the plane of the body to surface displacements related to an intrusion in the south flank of etna volcano sicily ground deformation was measured by a trilateration array and automatic tilt measurements during the 1989 eruption of the volcano significant line length changes and tilt were measured associated with an episodic 0 8 km propagation of the intrusion into the measurement array we incorporated the orientation and location of measured surface cracking into a bayesian nonlinear inversion of the data to determine the geometry of the intrusion we suggest the intrusion caused a 1 m wide opening of a vertical crack that extended from a depth of 1 km to within a few hundred meters of the surface we relate the distribution of surface cracking and seismicity associated with the fracture to stresses generated in the slip weakening zone associated with the crack edge

seismic activity accompanying the outbreak of the 1991 1993 eruption of mt etna italy abstract the character and location of seismic activity accompanying the onset of the 1991 1993 eruption at mt etna are compatible with the surface evidence of the volcanic pile rupture both the epicentral distribution and the focal mechanisms of a swarm that occurred on december 14 1991 agree with magma ascent occurring along the main nnw sse trending structure of the volcano and the consequent opening of a system of effusive fissures with the same trend a typical mainshock aftershock sequence recorded the day after and indicating transcurrent displacement occurring along the second principal structure of etna ne sw depicts the tectonic response of the volcanic pile and the underlying basement to major stresses applied by the magma push

very shallow earthquakes and brittle deformation in active volcanic areas the eatnean region as an example abstract some aspects of the stress field acting in active volcanic areas were investigated by studying the relationship between surficial seismicity h 1 2 km and the brittle deformation pattern of the etna volcano the magmatic composition and structural character of mt etna are described together with its geodynamic regional context after a discussion of the problem of the state of stress in active volcanoes and a definition of very shallow seismicity the high level of surficial seismicity the morphology of the sedimentary basement and the kinematic behaviour of the faults suggest that the eastern flank of mt etna is a shallow seismotectonic domain structurally decoupled from the rest of the volcanic body this flank shows a tendency to slide in an eastern direction and is bound to the north by a left lateral oblique slip normal fault trending e w and in the south by an arcuate fault system with right lateral features right lateral oblique slip normal faults

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

paleoclimatic forcing of magnetic susceptibility variations in alaskan loess during the late quaternary visual matches and statistical tests suggest correlations between marine isotope curves retrodictive solar insolation at lat 65 n and magnetic susceptibility profiles through late quaternary age alaskan loess sections the susceptibility changes largely appear to reflect variability in magnetite content due to climatically controlled changes in wind intensity and competence magnetic susceptibility profiles through massive loess can provide stratigraphic context for intercalated paleosols and tephras a prominent paleosol correlated with marine isotope stage 5 occurs several metres above the old crow ash in loess sections indicating that this important tephra is older than suggested by thermoluminescence dates and may have been deposited ca 215 25 ka

loess accumulation and soil formation in central kansas united states during the past 400 000 years based on interpolation of thermoluminescence dates and the mean accumulation rate of 0 034 mm yr 1 four cycles of pedogenic caco3 accumulation are found within the loveland loess 415 325 ka 325 250 ka 250 195 ka and 195 95 ka the four caco3 peaks correspond chronologically to marine oxygen isotope stages 11 9 7 and 5 respectively the early wisconsin 95 70 ka was characterized by sand dune activity the reddish pedocomplex was formed from 70 to 35 ka under relatively warm and moist climatic conditions with a very slow rate of silt accumulation 0 016 mm yr 1 the gilman canyon pedocomplex enriched in organic matter and dated at 35 20 ka was formed under a strong physical weathering regime and a relatively high rate of silt accumulation 0 15 mm yr 1 indicating a windy relatively moist probably cool environment it developed when the laurentide ice sheet was advancing and dust content in greenland ice core was low the peoria loess was accumulated at a rate of 0 3 mm yr 1 in central kansas under cold dry conditions when the ice sheet fluctuated around its maximum position and the dust content in the greenland ice core was the highest even the warm substage around 13 ka has some corresponding evidence in the central great plains the well developed brady soil dated at 10 5 8 5 ka indicates that the early holocene was the optimal time for soil development since 20 ka the poorly weathered bignell loess might have been deposited during the altithermal period from 8 5 to 6 ka

magnetic susceptibility of chinese loess and its bearing on paleoclimate magnetic susceptibility measurements are reported from 468 samples spanning a 160 m thick section of loess near the city of baoji shaanxi province an independent absolute chronology is provided by geomagnetic polarity reversals which indicate that the sediments represent the geological interval 0 to 2 5 million years ago fourier analysis of the susceptibility time series reveals strong spectral peaks at quasi periods of 100 000 and 40 000 years in agreement with the astronomical theory of climatic forcing the longer period is due to the eccentricity of the earth s orbit the shorter to the obliquity of the ecliptic the expected peak near 20 000 years due to precession appears only weakly however we do find strong evidence for a 400 000 year quasi periodicity particularly prior to 1 32 million years ago this is firmly predicted by astronomical calculations but has rarely been recognized in geological data

magnetic susceptibility of soils along a lithotoposequence in southeast iran abstract magnetic susceptibility is a simple and quick technique to determine soil properties and to describe soil forming processes knowledge about factors affecting data helps better interpretation magnetic susceptibility of soils along a lithotoposequence was studied in this research in order to investigate the effects of soil forming factors parent material and relief and processes on the content and its vertical distribution the study area is a transect from jiroft to kahnooj area south kerman province iran rock pediment mantled pediment inselberg alluvial fan alluvial plain and flood plain landforms with igneous parent materials gabbro diorite and granite were selected in the area thirteen representative pedons on different geomorphic positions were studied low frequency lf values ranged from 193 1 10 8 m3 kg 1 to 2704 2 10 8 m3 kg 1 in studied soils and decreased with increasing diamagnetic material contents mean lf values in soils formed on gabbro diorite and granite parent rock were 1700 10 8 m3 kg 1 515 22 10 8 m3 kg 1 and 352 53 10 8 m3 kg 1 respectively frequency dependent of soils in the range of 0 06 to 1 05 showed that coarse multi domain grains inherited from igneous parent material were the main source of lf in the area under study both increasing and decreasing trends of lf with depth were observed decreasing trend of lf with depth was due to illuviation of diamagnetic material into subsurface layers on the other hand increasing lf with depth was attributed to the primary ferrimagnetic material inherited from igneous parent material alluvial plain 320 44 10 8 m3 kg 1 and mantled pediment 328 50 10 8 m3 kg 1 showed low values of lf due to high amounts of soluble salts anhydrite and calcium carbonate investigated in these geomorphic positions a positive significant relationship r2 0 018 r 0 27 p

mt etna a model for the 1989 eruption abstract during the 1989 eruption of mt etna one of the most important in the last 20 years in terms of effusion rate a pair of fractures formed on the slopes of the southeast crater cone and propagated in a few days trending ca northeast and southeast with large quantities of magma being drained from the northern fracture in contrast the southern fracture after a short initial eruptive phase grew by 5 km in five days without eruptive or seismic activity when the fracture system crossed the southern scarp of the valle del bove wall some 6 km se of the active crater an intense seismic swarm started in the same area this lasted about four days and consisted of several hundred events clustering in a small focal volume although such a sequence of failure events contains elements of compatibility with a shallow dyke intrusion it did not lead to the expected flank eruption which would have threatened settlements just a few kilometres from the distal end of the fracture the question arises therefore whether or not the fracture system was dyke related and if so to what extent we attempt here to answer such a question by integration and interpretation of the available field observation and geophysical data indeed field observation constraints on the southern fracture system and the typical depth 2 km of the swarm do not contain evidence for shallow dyke emplacement beneath the lowermost part of the sse fracture conversely the inferred direction and shape of the tremor source the location and extent of a gravity anomaly observed a few months before the eruption the near horizontal migration of the seismic focii during the swarm and the change with time of related focal mechanisms lead us to hypothesize that the extreme development of the fracture system at its south was due to a deeper intrusion beneath the southern slope of the volcano

loess stratigraphy in central china abstract loess sequences in central china provide a detailed record of climate changes during the last 2 5 million years at least 44 major shifts from glacial to interglacial conditions occurred during this time in china prolonged loess deposition lasting more than 40 millennia occurred eleven times with only four of these intervals in brunhes chron the climate oscillations took place with increased frequency between 2 4 and 0 5 ma compared to the last half million years major shifts toward cooler and drier climates occurred at about 2 4 ma 1 2 ma and 0 5 ma while less pronounced shifts are dated to 1 65 ma 0 8 ma and 0 2 ma three of the last four reversals of the earth s magnetic field whose lithostratigraphic position has been detail are recorded in a glacial deposit the low field magnetic susceptibility of loess and soils which reflects the concentration of ultrafine magnetite is related to the degree of pedogenesis and serves as a proxy measure of climate the accumulation rate of the magnetite was fairly constant throughout the last 1 2 million years and can serve as a measure of time susceptibility records from localities near xifeng and luochuan located 160 km apart are compared and used to define informal lithostratigraphic units in the loess plateau of china

a mid late quaternary loess paleosol record in simmons farm in southern illinois usa abstract in unglaciated areas of the mississippi valley region the typical full loess paleosol succession contains the modern soil developed in peoria silt weakly developed farmdale geosol developed in roxana silt sangamon geosol developed in loveland silt and yarmouth geosol developed in crowley s ridge silt although a fifth loess called the marianna silt is reported at one area the paleosol that separates the crowley ridge and marianna silts is not well defined previous thermoluminescence tl and optical stimulated luminescence osl age chronology has suggested multiple phases of sangamon geosol developed in loveland silt but clear morphological evidence of polygenetic sangamon geosol profiles have not been found recently a thick loess paleosol sequence has been studied in the middle mississippi valley in unglaciated southern illinois usa soil morphology and analytical results revealed five loesses and associated paleosol units two sangamon bt horizons were found separated by a thick actk horizon interpreted to indicate two phases of sangamon geosol development this well preserved loess paleosol succession provides one of the most complete mid late quaternary loess records in the middle mississippi valley to date and is important for studying the stratigraphic framework and paleoclimate and environment changes

paleoclimatic significance of the mineral magnetic record of the chinese loess and paleosols the origins of the magnetic susceptibility variations of the chinese loess and paleosols are explored by scanning and transmission electron microscopy of magnetic extracts and by magnetic modeling of magnetic hysteresis data to provide quantified estimates of the major magnetic components microscopy identifies several distinct size and shape characteristics in the magnetic carriers lithogenic magnetites intact and abraded dominate the coarse grained magnetic fraction the smallest of the coarse grains is 2 i m the remaining magnetic materal is ultrafine in size with two types of magnetite particles present type a particles strongly resemble soil magnetites produced by inorganic precipitation type b particles which occur rarely are probably bacterial in origin quantitative modeling of these magnetic assemblages shows that over 90 of the susceptibility variations is accounted for by the superparamagnetic magnetite component compared to the loess units the paleosols are richer in magnetite particularly of superparamagnetic size and have a threefold higher ratio of magnetite to hematite we identify pedogenic formation of magnetite as the major contributor to the loess magnetic record matching this record against other paleoclimatic records we find an extremely high correlation with the standard 18o record the chinese loess sequences record a very high resolution magnetic stratigraphy directly related to changing climate

east asian monsoon climates and gobi dynamics in marine isotope stages 4 and 3 abstract several thick last glacial loess sequences in the western part of the chinese loess plateau and an eolian colluvial sequence in the central mongolian plateau are used to understand how the summer and winter monsoons responded to global forcing factors during marine isotope stages mis 4 and 3 the magnetic susceptibility data are compared with other climatic proxy data to improve the well publicized reconstruction of the past monsoons this study suggests that different sensitivities between the summer and winter monsoons in responding to the northern insolation resulted in transitional climates between marine isotope stages which were characterised by cold and wet climates in the western part of chinese loess plateau after forest steppe in mis 5 coniferous forest emerged at the mis 5 mis 4 transition in cold and moist conditions these imply that the lower latitude oceans were still capable of supplying water vapour to the continental interior and that the mongolian high became dominant when the northern insolation entered a stadial state mis 4 coniferous forest dominated mis 4 but thereafter deteriorated to a steppe towards the end of the mis 4 probably because the lower latitude oceans failed to supply water vapour to the interiors a coniferous forest emerged again at the mis 3 mis 2 transition after forest steppe in mis 3 consequently the southern boundary of the gobi desert retreated northwards during the coniferous tree dominated periods between 73 and 60 ka and between 27 and 19 ka and expanded to maxima between 60 and 50 ka and between 19 and 10 ka the extent of the gobi desert was considerably smaller for several times around 47 ka and 41 ka and 27 ka during mis 3 than during the holocene and the northern boundary retreated 5 times around 20 ka 24 ka 29 ka 31 ka and 34 ka in just the later part of mis 3

paleosubarctic eolian environments along the southern margin of the north american icesheet and the southern margin of siberia during the last glacial maximum abstract based on a negative correlation of magnetic susceptibility with organic matter content and the degree of gleying documented both in north american and southern siberian eolian sequences the authors propose that reducing conditions of incipient histosol development contributed to the alteration of magnetic minerals from strongly magnetic forms of oxidized iron to weakly magnetic forms therefore the magnetic susceptibility is basically an indicator of redox cycles well vegetated conditions generally dominated the later part of the last glacial maximum lgm 15 000 8000 14 c years bp and poorly vegetated conditions the early part 21 000 15 000 14 c years bp with a rapid transition around 15 000 14 c years bp chronologically corresponding to many well documented rapid transitions around the world the magnetic susceptibility signatures indicate approximately 1000 year long cycles of environmental changes during the last glacial maximum 21 000 10 000 14 c years bp in north america the initial perturbation of these 1000 year long cycles might have started in the tropical pacific and then been promptly transferred to the north atlantic via the north american icesheet the southern siberian eolian sequence recorded approximately 1400 year cycles these 1400 year cycles might have been associated with the thermal variations in the arctic ocean that was directly linked with the thermal variations in the north atlantic ocean to sum up our research suggests that the north american eolian sequence recorded 1000 year cycles and the southern siberian eolian sequence recorded 1400 year cycles although it is not able to propose plausible mechanisms controlling the 1000 or and 1400 year cycles

improving seismic surveillance at mt etna volcano by probabilistic earthquake location in a 3d model the increasing accuracy of 3d velocity models developed recently for mt etna has enabled their use today in routine earthquake locations in this work we tested the potential and performance of a global search probabilistic earthquake lo cation method nonlinloc in a 3d velocity model to improve earthquake locations for seismic surveillance in addition nonlinloc hypocenter locations and those ob tained by standard iterative linear 3d locations simulps 14 have also been com pared to this end a dataset of 328 selected earthquakes occurring during the 2002 2003 etna flank eruption and the recent highest resolution 3d velocity model have been used the results revealed that the differences in hypocentral coordinates between the two methods are typically of the same order or smaller than the spatial location uncertainty to evaluate the consistency of results between the two 3d location algorithms synthetic datasets with real source receiver configuration are also considered furthermore by using nonlinloc we estimated the influence of the source receiver geometry on the quality of hypocenter locations if we vary the net work geometry in a dense and well distributed network like at etna reducing the number of stations by 20 and 50 it is significant that no large systematic hypo central shifts of the relocated earthquakes are observed if they occur within the net work nonlinloc is a fast and promising approach for automatic earthquake locations and surveillance purposes at mt etna because 1 it works well with a reduced num ber of seismic pickings which are usually available in the automatic locations 2 it is not particularly sensitive to tolerable levels of random noise in arrival times and 3 it produces full location uncertainty and resolution information with respect to standard iterative linear 3d locations

isotopic and rock magnetic expression of environmental change at the pleistocene holocene transition in the central great plains abstract in a region too dry for the effective use of the traditional palynological approach loess deposits of the central great plains offer a source of proxy information for the reconstruction of past climates the brady soil a ubiquitous feature developed within the uppermost late pleistocene peoria loess recorded the character of vegetation change associated with climate shifts during the pleistocene holocene transition stable carbon isotope ratio analysis and two room temperature magnetic parameters were used to examine the nature of the change during this period 13 c values derived from soil organic matter indicate that in the late pleistocene minor populations of drought tolerant c4 plants were interspersed among the dominant cool season grasses c3 in the west while c3 grasses were accompanied by trees in the east by the early holocene c4 grasses were the dominant vegetation in the west and contributed substantially to the 13 c signal in the east magnitude of the 13 c shift suggests an increase in july mean daily temperature of 8 10 c according to existing models magnetic susceptibility and frequency dependence signal the cessation of loess deposition and development of the brady soil and indicate a spatial pattern in the intensity of weathering across the region

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

anomalies of seismic wave propagation at mt etna volcano italy abstract macroseismic and instrumental data concerning earthquakes that occurred in the etnean area during 1978 1987 have been used to reveal the possible anomalies in the propagation of seismic waves in the shallowest part of the volcanic edifice a set of 134 shocks located in different sectors of the volcano and having a depth not exceeding 5 8 km was used the availability of instrumental records and accurate macroseismic information made it possible to compare the epicentres derived from these two data sets time residuals obtained after fixing the macroseismic epicentre as the reference one were mapped for each permanent station of the local seismic network maps of residuals pointed out the existence of wide anomalies in the eastern sector of the volcano at a depth not greater than 4 5 km these anomalies strongly influence the seismic wave propagation so that the shallow part of the crustal model generally adopted should take them into account moreover a very shallow anomaly was detected in the upper parts of the southern sector of the volcano although based on a qualitative approach such findings strongly support the hypothesis that shallow volcanic structures and heterogeneity significantly influence the seismic energy propagation and they can be used to improve a three dimensional velocity model for the etnean area

characterisation of soils by mineral magnetic measurements processes of iron mineral authigenesis diagenesis and dissolution in interaction with primary inputs of iron minerals act to produce vertical differentiation of soil magnetic properties thus magnetic iron oxides in common with other iron forms may both respond to and reflect soil forming processes investigation of the degree of detectable and persistent magnetic differentiation within different soil materials can provide insights into the nature and direction of distinct sets of soil processes evidence of clear association between magnetic variation and discrete types of soil environment also has applied significance in several areas of environmental study for example the observed magnetic variation can be used to discriminate between individual soils and soil horizons for the purposes of soil surveying sediment tagging and tracing and empirical modelling of source sediment linkages this paper reports the use of mineral magnetic techniques to characterise the iron oxide assemblages within soils of varying type and provenance the effect of different pedogenic regimes have been investigated through measurement of a range of magnetic parameters including magnetic susceptibility frequency dependent susceptibility and anhysteretic and saturation remanences contrary to current pedological thought but in accord with other magnetically based studies e g mullins the presence of magnetite maghemite typically of superparamagnetic single domain grain size within soils has been found to be an extremely widespread phenomenon its contemporary neoformation within the soil environment is inferred however the input of artificially generated ferrimagnetic material is indicated for one of the magnetically enhanced soils examined here and the possibility of extraneous sources of magnetite in topsoils should be considered before pedogenic processes of magnetic enhancement are inferred from the data presented discrimination of industrially derived magnetic particles appears possible on the basis of their very low levels of frequency dependent susceptibility fd low anhysteretic remanence arm and dissociation from the finer clay sized not the formation but the active dissolution of ferrimagnetic minerals is indicated for soils affected by the processes of gleying and podsolisation eluvial horizons of podsolised profiles demonstrate almost total loss of detectable magnetic content variations in the form of the iron reprecipitated in the underlying illuvial layers may reflect differences in the pedological characteristics of these horizons within gleyed waterlogged soils processes of magnetite dissolution appear to be grain size specific preferential reduction of those grains of ultrafine superparamagnetic and fine single domain magnetic grain size is indicated where soil forms a major contributor to catchment sediment loads this has significance in the area of source sediment modelling soil derived from permanently wet or highly leached catchment areas is unlikely to contribute to peaks in the magnetic content of deposited sediments further only those erosional processes that operate at a faster rate than those of magnetic depletion will have the capacity to produce peaks in sediment ferrimagnetic concentrations such as have been observed within the historical magnetic record

rangeland management and fluvial geomorphology in northern tanzania abstract researchers have independently documented the effects of land use on rivers and threats to river management institutions but the relationship between changes in institutional context and river condition is not well described this study assesses the connections between resource management institutions land use and rivers by integrating social science geospatial analysis and geomorphology in particular we measured hydraulic geometry sediment size distributions and estimated sediment yield for four rivers in northern tanzania and conducted semistructured interviews that assessed corresponding resource management institutions communities managed rivers through both customary traditional nonstate and government institutions but the differences in the resource management policies and practices of the study rivers themselves were fairly subtle clearer differences were found at broader scales the four watersheds exhibited substantial differences in land cover change and sediment yield associated with the location of settlements roadways and cultivation unexpectedly these recent land use changes did not initiate a geomorphic response in rivers the long history of grazing by domestic and wild ungulates may have influenced water and sediment supplies such that river channel dimensions are more resistant to changes in land use than other systems or have already adjusted to predominant changes in boundary conditions this would suggest that not all rivers will have the anticipated responses to contemporary land use changes because of antecedent land use patterns over long time scales centuries to millennia the presence of grazers may actually increase the ability of rivers to withstand changes in land use our findings point to a need for further interdisciplinary study of dryland rivers and their shifts between system states especially in areas with a long history of grazing relatively recent changes in land use and a dynamic social and institutional context

discontinuous ephemeral streams abstract many ephemeral streams in western north america flowed over smooth valley floors before transformation from shallow discontinuous channels into deep arroyos these inherently unstable streams of semiarid regions are sensitive to short term climatic changes and to human impacts because hillslopes supply abundant sediment to infrequent large streamflow events discontinuous ephemeral streams appear to be constantly changing as they alternate between two primary modes of operation either aggradation or degradation may become dominant attainment of equilibrium conditions is brief disequilibrium is promoted by channel entrenchment that causes the fall of local base level and by deposition of channel fans that causes the rise of local base level these opposing base level processes in adjacent reaches are maintained by self enhancing feedback mechanisms the threshold between erosion and deposition is crossed when aggradational or degradational reaches shift upstream or downstream extension of entrenched reaches into channel fans tends to create continuous arroyos upvalley migration of fan apexes tends to create depositional valley floors with few stream channels less than 100 years is required for arroyo cutting but more than 500 years is required for complete aggradation of entrenched stream channels and valley floors discontinuous ephemeral streams have a repetitive sequence of streamflow characteristics that is as distinctive as sequences of meander bends or braided gravel bars in perennial rivers the sequence changes from degradation to aggradation headcuts concentrate sheetflow a single trunk channel conveys flow to the apex of a channel fan braided distributary channels end in an area of diverging sheetflow and converging sheetflow drains to headcuts the sequence is repeated at intervals ranging from 15 m for small streams to more than 10 km for large streams lithologic controls on the response of discontinuous ephemeral streams include 1 amount and size of sediment yielded from hillslopes 2 infiltration capacity of valley floor alluvium that influences both the unit stream power available for upstream headcut migration and the attenuation of flashy streamflow events by riparian vegetation in sheetflow reaches and 3 cohesiveness of alluvium which affects headcut and streambank morphology and rates of arroyo extension downcutting and widening initiation of arroyo cutting may be too complex to be attributed to a single cause such as change in mean annual precipitation or grazing by livestock but is most likely associated with a decrease in density of protective plant cover on hillsides and along valley floors relatively larger unit stream power makes downstream reaches more susceptible to initial entrenchment during floods than headwaters reaches and favors persistent arroyos entrenchment continues until an equilibrium longitudinal profile is briefly attained then channel widening occurs streambanks are undercut and aggradation begins

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

paleoenvironmental implications of rock magnetic properties of late quaternary sediment cores from the eastern equatorial atlantic rapid and nondestructive rock magnetic measurements of late quaternary sediment cores from the senegal continental slope and the sierra leone rise in the eastern equatorial atlantic correlate strongly with the specmap oxygen isotope master curve and carbonate content the rock magnetic paleoclimatic relationship results from differences in the concentration accumulation rate grain size and composition of magnetic minerals between glacials and interglacials at both sites magnetic mineral assemblages of glacial episodes are characterized by higher concentrations and accumulation rates of magnetic minerals by coarser grained ferrimagnetic minerals e g magnetite and by a lower ratio of ferrimagnetic to antiferromagnetic e g goethite hematite minerals by serving as a sensitive tracer for various deep sea sedimentary components rock magnetic properties can provide insights into changing sediment sources and fluxes and therefore are a useful addition to more traditional chemically and mineralogically based paleoceanographic techniques

magnetism of chinese loess deposits summary the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene and ascertained a maximum loess age of about 1 2 myr a new collection of nearly 500 samples from a natural outcrop and a borehole section near lochuan lat 35 8 n long 109 2 e shaanxi province has been dated by magnetic stratigraphy thermal cleaning of the natural remanent magnetization nrm removes a strong secondary component of viscous origin along the present geomagnetic field which resides largely in magnetite the characteristic nrm component is due to haematite which is thought to be of chemical origin rhythmical intensity variations of nrm and initial susceptibility depend on the loess lithology and may reflect climatic changes during loess deposition the palaeomagnetic results are consistent between the two sections and yield a clearly defined magnetic polarity zonation the brunhes matuyama boundary and the jaramillo subchron have been positively identified in both outcrops at exactly the same stratigraphic level the olduvai subchron has been found in the borehole section which records the entire loess sequence most probably the formation of chinese loess began shortly after the matuyama gauss polarity transition therefore a late pliocene age of about 2 4 myr is assigned to the oldest loess sediments measured

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

soil parent material relationship in a mountainous arid area of kopet dagh basin north east iran abstract the effects of parent rock types on soil evolution in arid areas were studied in a sequence of soils derived from different lithologies in the kopet dagh basin northeastern iran using micromorphology clay mineralogy magnetic susceptibility and physico chemical properties the selected parent rocks and associated soils were shale haplocalcids claystone haplotorrerts gypsiferous marl haplogypsids limestones haplocalcids and torriorthents siltstone and sandstones torriorthents the results showed that the properties and development of soils were mainly affected by grain size and mineralogy of parent materials soil magnetic susceptibility lf variations were attributed to the types of parent material and pedogenic processes redistribution of calcite and gypsum in soil profiles and natural and pedogenic formation of ferrimagnetic minerals were responsible for lf variations the soils clay mineral origins were found to be mainly of inheritance from parent materials smectite was the dominant clay mineral of the most soils based on the micromorphological index of soil evolution miseca the soils studied were categorized into weakly developed orthents weakly to moderately developed aridisols gypsids and calcids and moderately developed soils including calcids and torrerts the degree of microstructure development alteration of weatherable minerals and calcitic features were the most important criteria influencing assessment of soil development degree by miseca index the vertic features were only observed in soils of claystone in which there were considerable amounts of clay and smectite high amounts of gypsum and low smectite content were mainly responsible for the lack of vertic behavior in other fine grained soils derived from shale and marl

lithological factors affecting magnetic susceptibility of subtropical soils zhejiang province china abstract magnetic susceptibility was measured on subtropical soils formed on a range of parent materials in zhejiang province china to demonstrate the influence of parent material lithologies on the amount and vertical distribution of in the soils we found that the values of soils vary by up to two orders of magnitude with their parent material lithologies soils formed on igneous rocks with high values showed high absolute and distinctly decreased compared with values of parent materials the values of soils formed on basalt andesite and granodiorite were 250 10 8 m 3 kg 1 the values of soils formed on granite and other neutral and acid igneous rocks ranged from 50 10 8 to 120 10 8 m 3 kg 1 in most of the soils formed on sedimentary rocks enhancement in upper horizons of soils was found compared with parent material this enhancement was believed to be pedogenic formation of superparamagnetic sp stable single domain ssd magnetic grains which are characterized by high values of frequency dependent susceptibility fd and anhysteretic remanent magnetization arm soils formed on sedimentary rocks with a very low initial and iron content showed a low value throughout the profile it was found that there is a highly significant relationship between the values of soils and their dithionite citrate bicarbonate solution dcb soluble iron contents fe d the values of soils in chronosequences formed on alluvium and two marine deposits increased as soils became older it is suggested that the values can be used as a tool for determining the relative age in chronosequence studies

geographic variations in particle size distribution of the last interglacial pedocomplex s1 across the chinese loess plateau their chronological and pedogenic implications abstract due to northwestward attenuation of the summer monsoon and northwestward intensification of loess deposition during the last interglacial the last interglacial pedocomplex s1 gradually differentiated from the northwest to the southeast the three paleosols s1s1 s1s2 s1s3 corresponding to the marine isotope sub stages 5a 5c and 5e and the two intercalated loess units s1l1 s1l2 corresponding to the marine isotope sub stages 5b and 5d are completely preserved at northwestern sections towards southeast both the s1l1 and s1l2 were annexed by the subsequent paleosol development s1s1 and s1s2 and the three paleosols s1s1 s1s2 and s1s3 were partially welded at the southeasternmost site the three soil forming events s1s1 s1s2 and s1s3 repeatedly occurred in a single paleosol profile the three observed orders of particle size variations are interpreted to have imprinted important chronological and pedogenic signatures first order variations i e a remarkable difference between the interglacial pedocomplex s1 and the glacial loess units l1 and l2 implies that the s1 parent material was considerably finer in the source areas or and the proximity to the source areas was much farther during interglacial period than during the preceding l2 and following l1 glacial periods second order variation i e the parenthetical trends in 63 m and

first application of asdp software a case study at mt etna volcano and in the acri region southern italy abstract the pc based automatic seismic data processing asdp software module uses a multi algorithm approach and a new procedure msa for signal detection phase grouping and event identification and location it is designed for an efficient and accurate processing of local earthquakes records provided by single site and array stations results from asdp processing of two different data sets are analysed to evaluate its performance by comparing of asdp pickings with those revised manually the detection and subsequently the location capabilities of this software are assessed the first data set is composed of 330 local microearthquakes 1 7 m 3 8 recorded in the mt etna volcano area by a telemetered analog seismic network digital data conversion of data is performed at the network centre operated by the istituto internazionale di vulcanologia of c n r the second data set comprises 40 ultra microearthquakes 0 5 m 2 0 recorded by a temporary array of four digital three component stations deployed in the acri region southern calabria for the etnean earthquakes a comparison of the automatic results with the manual picks indicates that the asdp module can accurately pick 80 of the p waves differences are within 0 15 s and 65 of the s waves differences are within 0 3 s a peculiarity for these events is that the majority of the 3 three component station records do not exhibit distinct s waves this statistics includes records with a strong noise ground tremors and or system electronic disturbances but does not include false alarms due to non seismic signals conversely if we consider high dynamic recordings of seismic digital data in a low noise environment acri temporary array the asdp module can accurately pick 93 of the p waves differences with manual estimations are less than 0 1 s and 87 of the s waves differences with manual estimations are less than 0 2 s for this type of data with a favourable signal to noise ratio the automatic back azimuths estimates are also extremely accurate in the 87 of the cases differences estimations with those revised by an analyst and deriving from hypocenter solutions are generally within 10 in general our results indicate that both automatic asdp and manual hypocenter locations are comparable within the estimated errors bounds furthermore the comparison of asdp automatic locations with those performed by xrtp iaspei software routinely used for automatic locations at the mt etna seismic network indicates a better performance of the asdp module

the hidden nature of parent material in soils of italian mountain ecosystems abstract soils with andic features are known to be very important as regards both ecosystem fertility and susceptibility to land degradation in recent years there has been an increasing number of finds of these soils in non volcanic mountain ecosystems nvme in different parts of the world under different environmental settings in italian nvme there has been extensive investigation proving that these soils have a much wider distribution than previously thought but despite these important findings very little is known about their genesis or properties against this background our investigation aims to question the nature of parent material in andic soils in italian nvme we consider this question fundamental for proper understanding of such soils we address the question of the parent material by highlighting similarities dissimilarities between soils and their underlying bedrocks and ascertaining whether soils developed as a result of in situ weathering or because of eolian inputs the study was conducted on 41 soil profiles distributed throughout italian nvme performing an integrated analysis of i grain size distribution gsd by laser granulometry ii end member modelling of obtained gsd iii soil bedrock differences in magnetic susceptibility and iv soil bedrock differences based on the geochemistry of 38 elements the final results from these investigations show that the investigated soils are mainly derived from eolian sediments and that weathering of the underlying bedrock plays a minor role two main types of eolian parent materials seem to coexist in different proportions according to the soil type eolian sediments with a similar composition of the underlying bedrock termed autochthonous loess and eolian sediments of volcanic type pyroclasts autochthonous loess represents the main component of the parent material in the following studied soils aluandic andosols cambisols phaeozems and podzol 67 63 44 and 73 respectively all these soils exhibit low to moderate andic features volcanic type eolian sediments constitute about 90 of the parent material in most andic soils that are silandic andosols but occur in different proportions in most of the investigated soils the nature of soil parent materials surprisingly follows a clear trend with latitude with autochthonous loess characterizing most parent materials in northern italy whilst volcanic sediments form most parent materials in the south in accordance with their latitude other soils exhibit an intermediate behaviour

10be and magnetic susceptibility in chinese loess 10be and magnetic susceptibility have been measured in the top 12 m of a loess profile from luochuan central china comparison of the 10be concentration record with the specmap 18o profile of the last 130 ka imbrie et al 1984 results in a new time scale which is in good agreement with that of kukla et al 1990 the calculated loess accumulation rates can be compared with existing records of dust falls in pacific deep sea sediments and antarctic ice cores a simple model for the 10be dust flux demonstrates that a significant part of the magnetic susceptibility signal in palaeosol horizons is due to in situ pedogenic production during times of high loess accumulation cold palaeoclimate this contribution is negligible

dynamic inversion of ground deformation data for modelling volcanic sources etna 1991 93 the 1991 93 etna eruption that represented the most important recent eruptive event both in terms of duration 472 days and total volume of erupted lava ca 250 106 m caused marked ground deformation measured by using different geodetic techniques such as edm gps levelling and tiltmetry an inversion termed dynamic because it took into account the sequence of events considering both the separate and cumulative effects of two sources a shallow tensile crack and a deeper ellipsoidal deflating source was performed it was based on 163 data collected by the different techniques plus 2 geometrical conditions for constraining the geometry of the crack on the surface the final solution furnished a good fit for all measurements defining a shallow tensile crack located inside the volcanic edifice which represents the effect of the intrusion and a depressuring body with centre at ca 3000 m b s l which could represent the centre of a generalized and more complex deflation of the volcanic edifice during the course of the eruption

importance of gravitational spreading in the tectonic and volcanic evolution of mount etna the interaction between gravity and thermal effects largely determines the structural and magmatic evolution of volcanic constructs at scales spanning several orders of magnitude from small cones to the oceanic crust1 3 although gravitational spreading is a direct consequence of this interaction and a fundamental process in volcano growth it is rarely recognized as such here we describe a striking example of this process at etna volcano in italy the volcano and its clay rich substratum are slowly spreading towards the east and south driven by gravity spreading produces extensional structures in the summit region and contpressional structures at the base of the volcano eastward movement of the volcanic edifice over a stationary magma supply may be the cause of an apparent westward migration of volcanic activity as gravitational spreading seems to control the location and magnitude of shallow seismicity and flank eruptions an appreciation of its effects could become an essential element of future volcanic hazard evaluation our model proposed here for etna may also be relevant to a reinterpretation of the geological history of a number of other volcanoes

location and orientation of eruptive fissures and feederdykes at mount etna influence of gravitational and regional tectonic stress regimes abstract lava extrusion from fissures on the flanks of the etna volcano is a common feature of recent activity as evidenced by the eruptions of 1971 1981 1983 and 1985 and was of similar importance during prehistoric times we propose here a model within which the location and orientations of the large majority of historic eruptive fissures on etna s flanks together with their feeder dykes are explained within the framework of a gravitational stress regime stress orientations within this regime are controlled largely by the gross morphology of the volcano but are significantly modified by local topographic anomalies we propose that the gravitational stress regime largely supercedes an earlier developed regional tectonic stress regime which still operates in the sub volcanic basement and may remain the dominant control of eruptive fissure and feeder dyke disposition at lower altitudes on the flanks the proposed model is supported by 1 detailed examination of fissure locations and orientations and the relationship between fissure azimuths and topography 2 precise horizontal distance measurement and vertical ground deformation studies of a recent eruption and 3 qualitative physical modelling experiments in which coloured water is injected into solidified gelatine solutions representing variously shaped volcanic constructs a cautious approach is advocated when extrapolating trends of spatially limited fissure segments for the purpose of locating potential sites of magma ascent and implications of the model for hazard analysis are outlined

pedogenic factors affecting magnetic susceptibility of the last interglacial palaeosol s1 in the chinese loess plateau the magnetic susceptibility has been used as a quantitative or semi quantitative proxy for reconstructing the summer monsoon intensity in the chinese loess plateau based on extensive studies on climatic or and environmental mechanisms producing the magnetic susceptibility signatures however the precise nature of the link between past climates and the susceptibility signatures has remained uncertain primarily due to lack of our understanding in the nalizing and preserving processes of the signatures this paper attempts to examine the reliability or acceptability of this summer monsoon proxy from non magnetic perspectives of soil forming processes we chose nine sections along two transects one across the western part of the chinese loess plateau and another across the eastern part several conclusions can be drawn from our analytical data first clay translocation within the s1 palaeosol pro les as indicated by eld observed clay coatings on ped faces in bt and bk horizons and demonstrated by laboratory analysed clay contents must have moved some of the magnetic minerals downward so that the susceptibility re ects only the post translocation distribution of the magnetic susceptibility producing minerals second the best developed palaeosol s1s3 at most of the sections studied is not expressed by the magnetic susceptibility because this palaeosol developed in underlying coarse loess l2 and coarse textures tend to lower the susceptibility third carbonate concentration is normally negatively correlated with the magnetic susceptibility or simply suppresses the magnetic susceptibility peak when the susceptibility enhancement exceeds the carbonate dilution effect to conclude extreme caution must be observed when using magnetic susceptibility signatures to retrieve high resolution records of the last interglacial palaeoclimate in the chinese loess plateau copyright 2004 john wiley sons ltd

effects of land use change on channel morphology in northeastern puerto rico between 1830 and 1950 much of northeastern puerto rico was cleared for agriculture runoff increased by 50 and sediment supply to the river channels increased by more than an order of magnitude much of the land clearance extended to steep valley slopes resulting in widespread gullying and landslides and a large load of coarse sediments delivered to the stream channels a shift from agriculture to industrial and residential land uses over the past 50 yr has maintained the elevated runoff while sediment supply has decreased allowing the rivers to begin removing coarse sediment stored within their channels the size abundance and stratigraphic elevation of in channel gravel bar deposits increases channel depth decreases and the frequency of overbank flooding increases downstream along these channels this is presumed to be a transient state and continued transport will lead to degradation of the bed in downstream sections as the channel adjusts to the modern supply of water and sediment a downstream decrease in channel size is contrary to the expected geometry of self adjusted channels but is consistent with the presence of partially evacuated sediment remaining from the earlier agricultural period reverse downstream decreasing channel morphology is not often cited in the literature although consistent observations are available from areas with similar land use history identification of reverse channel morphology along individual watercourses may be obscured in multiwatershed compilations in which other factors produce a consistent but scattered downstream trend identification of reverse channel morphology along individual streams in areas with similar land use history would be useful for identifying channel disequilibrium and anticipating future channel adjustments

palaeoclimatic implications of the magnetic record from loess palaeosol sequence viatovo ne bulgaria summary loess palaeosol deposits in the lower danube area represent the southeastern edge of the loess cover in europe detailed rock magnetic investigations of the loess palaeosol sequence in viatovo in ne bulgaria reveal that magnetite and maghemite of very fine superparamagnetic grain size are responsible for the magnetic enhancement of palaeosol units a detailed palaeoclimatic record is obtained through high resolution measurements of magnetic susceptibility frequency dependent magnetic susceptibility and caco3 content magnetic proxies indicate a more warm and humid climate during the development of the older palaeosol units s4 s6

late quaternary dust flow on the chinese loess plateau abstract the dust flux of over 25 g cm2 103yr was reached in the central part of the chinese loess plateau during the last glacial maximum this is more than three times higher than during the last interglacial and early glacial time the grain size of the pleniglacial dust reached a peak shortly after 20 000 years ago and testifies to the occurrence of strong winds and frequent dust storms

magnetic parameters indicate the intensity of chemical weathering developed on igneous rocks in china abstract continental weathering plays a key role in earth surface processes by linking earth s spheres and producing material for cycling previous studies have proposed numerous weathering indices for the evaluation of chemical weathering intensity however few research efforts are devoted to the changes of sediment physical properties during weathering processes and on the correlations between weathering and mineralogical chemical alteration this study investigates mineral transformation and magnetic properties of two weathering profiles developed on granodiorite and basalt in china the notable differences in magnetic properties between the two profiles i e magnetic susceptibility percentage frequency dependent susceptibility fd anhysteretic remanent magnetization arm and saturation isothermal remnant magnetization sirm are ascribed to the combined effects of parent rock lithology and climate conditions on the formation and alteration of magnetic components during weathering pedogenesis parent rock lithology e g fe bearing basalts and relatively fe poor granites determines the initial magnetic susceptibilities warm and humid climate favors rock weathering and thus enhances the magnetic intensity whereas changes in redox conditions lead to inhomogeneous degree of chemical weathering and thus alter the spatial distribution of magnetic minerals this study further suggests that the weathering intensity in geologic profiles can be evaluated by magnetic indicators such as fd and arm sirm based on their positive correlations with the chemical index of alteration cia the research findings may shed new light on the constraints on continental weathering and detrital sediment cycling in the east asian continental margin

magnetic susceptibility and morphological characteristics of a loess paleosol sequence in northeastern iran abstract magnetic susceptibility of loess paleosol sequences is frequently used for paleoclimatic and paleoenvironmental studies a penultimate loess paleosol tappeh salam section from northeastern iran was studied to determine i morphologic sedimentologic and magnetic characteristics of the section ii the effect of high amount of carbonates and gypsum on the magnetic susceptibility and iii if any recognizable relationship between magnetic susceptibility and paleoenvironmental conditions during periods of soil formation and loess deposition existed the bulk magnetic susceptibility lfbulk of genetic horizons was measured to eliminate the effect of gypsum and carbonates the minerogenic magnetic susceptibility lfminero was calculated based on morphological characteristics five distinct parts were recognized part 1 and 4 are composed of unaltered loess deposits with easily visible gypsum crystals part 2 includes a series of bw by and bk horizons that ends to a last interglacial paleosol with a btk horizon in part 3 at the base of the section because of its extremely hard consistency part 5 has an abrupt boundary the lfbulk values of different layers of the horizons change from 40 9 10 8 m3 kg 1 in the weakly developed part 1 to 75 6 10 8 m3 kg 1 in the btk horizon the amount of gypsum plus carbonates is 13 6 40 9 making the interpretation of lfbulk difficult the lfminero makes the difference clearer through the section the lfminero of part 1 is 108 9 10 8 m3 kg 1 this unexpectedly high value may be expressed by anthropogenic addition of magnetic particles the lfminero of btk horizon exceeds 103 10 8 m3 kg 1 showing the effect of accumulation of iron oxides during warm and humid climate of the last interglacial period the 70 10 8 m3 kg 1 value for lfminero in part 4 can be attributed to parent materials part 5 has the lowest lfminero of 50 10 8 m3 kg 1 hydromorphic conditions in part 5 has induced the decomposition of iron oxide resulting in a decline in magnetic susceptibility the results of this study show the effectiveness of magnetic susceptibility properties for the interpretation of paleopedological and paleoenvironmental conditions of loess paleosol sequence in northeastern iran it should be noted that in the arid regions to avoid misinterpretation the effect of high amount of gypsum and carbonates must be taken into account by minerogenic magnetic susceptibility calculation

baoji type pedostratigraphic section loess plateau north central china abstract the baoji section is judged to be the most complete pedostratigraphic section on the loess plateau of north central china it is located about 5 km north of the city of baoji and consists of 37 paleosols formed during more than the last 2 5 ma it is designated here as the type pedostratigraphic section with formally named geosols following the rules of the north american commission on stratigraphic nomenclature geochronological control is based largely on magnetostratigraphy with the brunhes matuyama and gauss epochs and jaramillo and olduvai events clearly recognized the baoji geosols can be correlated with equivalent pedostratigraphic units throughout the loess plateau by a combination of magnetostratigraphy and character position and the association of the pedostratigraphic units within the quaternary succession the variation of the geosols suggests climatic cycles of varying intensity and duration but generally warmer and moister conditions when compared with the loess units that suggest colder and drier periods

10be in chinese loess we report a first series of10be measurements on chinese loess covering the last 750 000 years the10be concentration shows a tendency to decrease with increasing grain size leaching experiments with acid solutions show that10be is strongly bound to particles and therefore mobility due to dissolution can be excluded the10be record in loess shows features similar to those observed in 180 records from deep sea sediments which strongly reflect climatic variations this allows one to correlate the10be loess records with 180 deep sea records and to establish a time scale based on this time scale accumulation rates of loess and10be fluxes can be calculated these reveal generally higher values for cold arid and windy periods than for warm humid and calmer intervals

factors affecting the magnetic susceptibility of a loess soil sequence barton county kansas usa abstract to interpret climatic signatures from magnetic susceptibility ms in the barton county loess soil sequence central kansas we tested the influence of particle size and carbonate concentration on magnetic susceptibility first sand silt and clay were separated and ms was then measured on each of the three size fractions to assess the influence of chemical treatments and carbonate on ms signals the chemical agents used to remove carbonate organic matter and free iron oxides were applied to another set of samples and ms was measured before and after each of the treatments the results show that the bulk ms differentiates among stratigraphic units but the environmental interpretation is far from straightforward soils have stronger ms signals than the loess units in the upper portion while the carbonate rich soils have weaker ms signals in the lower portion due to the ms dilution effect of carbonate sand ms peaks in bignell loess peoria loess and ll1 may suggest that in loess units fewer sand sized magnetic minerals were changed by weathering processes into clay sized magnetic minerals than in soils a low bulk ms at the bottom of the reddish pedocomplex to the bottom of ls 1 is attributable to a combination of a high sand content and a high carbonate concentration the silt ms peak in the barton sand might have been derived from the parent materials comparing with mineralogic and chemical indices clay ms might be closer to being a proxy of weathering intensity although clay ms dominates the bulk ms signals silt ms and sand ms affect the bulk ms signals in two ways 1 changes in the percentages of silt and sand and 2 mineralogical variations in silt ms and sand ms from one stratigraphic unit to another this study demonstrates that 40 of the variation in the bulk ms is accounted for by the clay ms and 56 of the variation by the silt ms and clay ms together after adding the sand ms 66 of the variation is accounted for if diamagnetic carbonate is taken into consideration 76 of the variation in bulk ms is accounted for by the ms of the three size fractions and the ms dilute effect of carbonate

geochemical investigations applied to active fault detection in a volcanic area the north east rift on mt etna sicily italy geochemical investigations were performed on the northeast rift of mt etna a prominent volcanic structure of this volcano low temperature fumaroles were found on the upper part of this area and the isotopic compositions of c co2 and he suggest a likely magmatic origin of the emitted gases on the contrary very low degassing was found in the lower part of the ne rift with co2 concentrations generally very close to those in air this pattern is probably due to sealing of the eruptive fissures by the repeated injections of magma solidified into dikes and by consequent shallow hydrothermal alteration of the fissured rocks due to residual magma degassing high soil co2 concentrations were also found in an elongated area parallel to the ne rift and located immediately to the east of it the geometry of these anomalies suggests the existence of several hidden faults sub parallel to the ne rift and likely connected to the pernicana fault system this latter structure seems to merge with the ne rift at the altitude where the fumarole emissions are located the hidden structures together with the pernicana system and the ne rift represent the western and northern boundaries of a large eastward collapsing sector of mt etna

mineral magnetic record of the chinese loess and paleosols variations in the magnetic susceptiblity of the chinese loess and its interbedded paleosols correlate strikingly well with the deep sea oxygen isotope record low susceptibility values are found for the loess layers and high values are found for the soil horizons two interpretative models have been advanced to account for these magnetic variations both of these models discount any significant in situ formation of magnetite during soil forming periods instead they infer relative concentration of detrital or atmospheric magnetite at these times we critically examine the assumptions made in these models and on the basis of some new mineral magnetic data and fromalized magnetic flux calculations offer an alternative explanation of the loess magnetic record our model identifies pedogenic formation of magnetite as the major contributor to the high magnetic susceptibility of the paleosols the formation and preservation of this pedogenic magnetite is dependent on soil froming conditions and hence reflects the regional climate

holocene climatic and environmental changes in the arid and semi arid areas of china a review this paper reviews recently published literature most of which was published in chinese and searches for regional patterns of holocene changes useful in depicting global patterns the holocene in the xinjiang region can be divided into three stages a warming and dry early stage from 11 similar to 10 to 8 similar to 7 ka bp a warm and wet middle stage from 8 similar to 7 to 4 5 similar to 3 ka bp and a fluctuating cool and dry late stage since 4 5 similar to 3 ka bp the holocene in the northern tibetan plateau can also be divided into three stages a warming and wet stage from 10 5 similar to 10 to 5 similar to 4 ka bp followed by a variable drying and probably warm stage 5 similar to 4 to 3 ka bp and ending with a cool and dry stage since 3 ka bp in the inner mongolian plateau the early holocene from 10 5 similar to 9 5 to 8 similar to 7 5 ka bp was warming and dry and a warm and wet climate occurred from 7 5 to 3 5 during which the best time was 6 3 3 8 ka bp the climate has been variably drying and probably cooling since 3 5 ka bp in the northwestern part of the loess plateau several holocene palaeosols have been identified 10 9 7 5 5 4 3 and 2 7 2 ka bp with the 7 5 5 ka bp palaeosol being most strongly expressed the best developed palaeosol equivalent in major valleys is a swamp wetland facies deposited between 8885 and 3805 c 14 yr bp under an extremely wet regime the climate has fluctuated significantly at least three times around a dry and probably cool regime after the swamp wetland facies depositional period our summary shows that the holocene climatic optimum occurred nearly contemporaneously 8 5 ka bp at all sites in the xinjiang region in the inner mongolian plateau and in the northwestern part of the loess plateau a warming and wet early holocene 10 8 ka bp in the northern tibetan plateau is most likely related to high effective soil moisture resulting from snow and ice melting we propose here that the middle holocene climatic optimum 8 5 ka bp in arid to semi arid china was primarily a delayed response of the low latitude oceans to high latitude peak insolation 9 8 ka bp

the human role in changing river channels abstract direct consequences of the human role where human activity affects river channels through engineering works including channelization dam construction diversion and culverting have been long recognised marsh 1864 thomas 1956 the less obvious indirect effects of point and reach changes occurring downstream and throughout the basin however are much more recently appreciated dating from key contributions by strahler strahler a n 1956 the nature of induced erosion and aggradation in w l thomas ed man s role in changing the face of the earth university of chicago press chicago 621 638 wolman wolman m g 1967 a cycle of sedimentation and erosion in urban river channels geografiska annaler 49a 385 95 schumm schumm s a 1969 river metamorphosis proceedings american society of civil engineers journal hydraulics division 95 255 73 and graf graf w l 1977 the rate law in fluvial geomorphology american journal of science 277 178 191 these are complemented by effects of alterations of land use such as deforestation intensive agriculture and incidence of fire with the most extreme effects produced by building activity and urbanisation changing river channels are most evident in the channel cross section where changes of size shape and composition are now well established with up to tenfold increases or decreases illustrated by results from more than 200 world studies in addition the overall channel planform the network and the ecology have changed specific terms have become associated with changing river channels including enlargement shrinkage and metamorphosis although the scope of adjustment has been established it has not always been possible to predict what will happen in a particular location because of complex response and contingency the ways in which changes in cross section relate to reach and network changes are less clear despite investigations showing the distribution of changes along segmented channels when considering the human role in relation to changing river channels at least five challenges persist first because prediction of the nature and amount of likely change at a particular location is not certain and because the contrasting responses of humid and arid systems needs to be considered modelling is required to reduce uncertainty as was first emphasised by burkham burkham d e 1981 uncertainties resulting from changes in river form american society civil engineers proceedings journal hydraulics division 107 593 610 second feedback effects incorporated within the relationship between changes at channel reach and network scales can have considerable implications especially because changes now evident may have occurred or have been initiated under different environmental conditions third consideration of global climate change is imperative when considering channel sensitivity and responses to threshold conditions fourth channel design involving geomorphology should now be an integral part of restoration procedures this requires fifthly greater awareness of different cultures as a basis for understanding constraints imposed by legislative frameworks better understanding of the ways in which the perception of the human role in changing river channels varies with culture as well as varying over time should enhance application of design for river channel landscapes

different styles of deformation in the calabrian arc southern italy implications for a seismotectonic zoning abstract the most recent seismic profiles in southern italy show the existence of a sudden thinning of the crust at the boundary between the chain and the tyrrhenian margin the abrupt change in thickness can be followed along a zone which has the same geometry in plan as the calabrian arc by considering these data and the gravimetric anomalies it is possible to associate this crustal anomaly with a deep seated shear zone which determines a crustal shortening of about 40 60 km which can only be a consequence of post tortonian tectonics the surface equivalents of the deep seated shear zone can be recognized from north to south in the alignment of the intra apenninic basins vallo di diano san arcangelo potenza in the crati mesima graben and in the mount kumeta alcantara fault zone the distribution of the seismicity and its connection with the surface structures shows that the largest earthquakes occur along the deep shear zone in particular shocks with the highest magnitude and the longest recurrence intervals are located in those areas where the deep shear zone is at an angle of about 90 with the direction of maximum shortening crati mesima graben the fault zones nearly parallel to the regional compression axis e g mount kumeta alcantara fault zone are characterized by earthquakes of lower magnitude taking into account the neotectonic evolution of the regional structures as well as the orientation of the stress field and its connection with the deep seated shear zone it is possible to distinguish the following seismotectonic zones upper crati mesima graben transverse throughs mount pollino mount raparo fault zone external ionian area san arcangelo basin zone of the external flysch sicani mountains mount kumeta alcantara fault zone caltanissetta basin and iblean plateau bradanic trough murge ridge the definition of the geometry of the shear zone at depth is one of the most important but still unresolved problems

actively growing anticlines beneath catania from the distal motion of mount etna s decollement measured by sar interferometry and gps we used sar interferometry and gps to measure the rise of an anticline beneath the urban area of catania italy which originates from outward thrusting above the basal decollement of etna volcano the anticline grows at a rate of over 0 015 m a 1 of se thrusting and about 0 007 m a 1 of relative uplift by relating this growth to the simultaneous extension measured at the summit of the volcano we demonstrate the occurrence of active volcanic spreading this process may exert a control on eruptions earthquakes sector collapses and landslides

high resolution proxy record of holocene climate from a loess section in southwestern nebraska usa abstract multi proxy analysis was used to produce a high resolution paleoclimatic record from an exceptionally thick section of the holocene bignell loess near wauneta southwestern nebraska in the central great plains the wauneta section has excellent age control based on optically stimulated luminescence osl and radiocarbon dating and records multiple episodes of rapid loess deposition alternating with slower deposition and soil formation the lowermost and uppermost osl ages obtained from the bignell loess are 10 250 610 years 5 9 m depth and 100 10 years 0 1 m depth respectively as a result the holocene has been temporally confined stratigraphically the bignell loess overlies the late pleistocene peoria loess deposited 21 14 ka and the two units are separated by the brady soil which is distinguished by its color and other pedogenic features l a b color parameters and organic carbon content of bignell loess are sensitive proxies to differentiate drought induced aeolian sediment layers from the intercalated soil horizons soil organic carbon derived 13 c data suggest that the c 3 dominated floral environment during peoria loess deposition shifted dramatically to a c 4 dominated environment during brady soil formation in response to a warming trend even greater c 4 abundance characterized the late holocene high resolution 13 c data support the contention that c 3 vs c 4 vegetation change in the holocene reflects ecosystem response to frequent vegetation disturbance under arid conditions time series analysis reveals that 13 c and color parameters display high frequency variation with periodicities of 103 118 years and 103 years respectively similar periodicities were also reported in studies of north dakota lakes though the physical mechanism responsible is uncertain comparison of bignell loess color and tropical pacific sea surface temperatures ssts allows evaluation of a proposed teleconnection between drought in the great plains and la nina like conditions in the tropical pacific the loess color index and eastern tropical pacific sst display broad similarities through the late pleistocene and holocene that are consistent with this teleconnection on the other hand drought centered at 3800 years ago is not consistent with the teleconnection and the end of early holocene aridity at the wauneta section around 6500 years ago is much earlier than the corresponding rise in sst and increase in el nino frequency in the eastern tropical pacific

palaeoclimatic and sedimentary history from magnetic susceptibility of loess in china the magnetostratigraphic age of the oldest loess sediments in the central chinese loess plateau investigated so far has recently been placed at ca 2 4 million years b p thus glaciations in central asia which are believed to provide the detritus for the formation of chinese loess commenced at the same time as the first ice rafted debris sank into the ocean basins of the northern hemisphere shackleton et al 1984 lithologic palaeontologic geochemical and especially rock magnetic variations throughout the loess column are indicative of palaeoclimatic fluctuations during loess deposition the variations of magnetic low field susceptibility in loess closely resemble those of the marine oxygen isotope record shackleton and opdyke 1976 and establish for the first time a continuous record of the pleistocene glacial and interglacial stages in a continental section spectral analysis of the rock magnetic time series indicates slow apparent sedimentation during interglacial periods which are characterized mainly by calcium dissolution and related compaction of the soils variable aeolic sediment influx as well as erosion and or polygenetic soil formation may also strongly influence the sedimentary history

evidence for the dissolution of magnetite in recent scottish peats abstract magnetic hydrological and geochemical data for 11 scottish peat cores confirm previous reports that anthropogenic pollutants constitute the principal source of ferrimagnets to such environments but indicate that postdepositional fe3o4 persistence may be more limited than formerly envisaged in all cores the lower stratigraphic limit of magnetic enrichment coincides with the water table below which negative mv values and enhanced ratios of fe mn and cu zn depict an abrupt transition to a strongly anoxic regime dissolution of fe3o4 in the reducing inundated zone is also signified by the more rapid down core loss of magnetic properties in cores from topographically depressed sphagnum lawns than in those from more elevated calluna hummocks as a consequence the peak and cumulative sirm values for cores from the former settings appear disproportionately low and the magnetostratigraphic records from adjacent but topographically variant sites are frequently asynchronous in contrast to most marine and lacustrine sediments dissolution of fe3o4 in peat induces a refinement of magnetic mineral assemblages highlighted by declining sirm arm ratios with depth and a hardening of remanence near the base of the magnetically enhanced strata sem micrographs of magnetic extracts from one scottish core indicate that this refinement results from preferential dissolution along crystallographic weaknesses within multidomain phases ultimately causing their disintegration and the adoption of single domain type magnetic behavior rates of dissolution are considerably greater than those reported for marine sediments probably due to the unusually high dissolved sulfide concentrations in mire waters

gobi dynamics in the northern mongolian plateau during the past 20 000 yr preliminary results abstract this study focuses on the khyaraany sand loess soil section 50 2 n 106 7 e in the northern mongolian plateau with the aim of deciphering the paleoenvironmental records and inferring the last glacial gobi dynamics the main findings are as follows 1 silt percentage with a negligible clay percentage is positively correlated with the organic matter content 2 the silt and frequency dependent magnetic susceptibility are negatively correlated 3 the magnetic susceptibility is positively related to sand percentage and negatively to silt percentage based on 14c dates and the extrapolated ages the following observations can be made 1 unlike the marine isotope stage mis 3 paleosols 24 500 28 900 30 700 34 400 yr bp that formed under oxidizing dominated conditions two mis 2 paleosols 15 090 13 030 yr bp and two holocene paleosols 8300 4070 yr bp were formed under dominantly reducing conditions 2 less windy and or better vegetation conditions generally dominated the later part of the last glacial 15 090 8300 yr bp during which three paleosols incipient histosols were formed 15 090 13 030 8300 yr bp 3 windy and or poor vegetation conditions generally dominated the early part of the last glacial 24 000 16 000 yr bp 4 this section documents approximately thousand year long redox cycles two tentative conclusions can be drawn from this and previous feng et al 1998 studies 1 the northern boundary of the gobi has shrunk as many as nine times during the past 40 000 yr around 34 400 30 700 28 900 24 500 15 090 13 030 8300 4070 yr bp and the recent 2000 yr 2 based on the negative correlation of the susceptibility with silt percentage and organic matter content it is proposed that the reducing conditions of incipient histosol formations have contributed to the alteration of magnetic minerals from strong forms of oxidized iron to weak forms therefore the magnetic susceptibility is basically an indicator of redox cycles

climatic signals from loess soil sequences in the central great plains usa abstract late quaternary eolian deposits and buried soils in the central great plains are interpreted to reflect the fluctuation of climatic conditions under which they formed the loveland loess was deposited approximately between 500 and 100 ka within the loess are four zones of pedogenic carbonate accumulation after 416 35 ka before 260 25 ka around 193 22 ka and before 92 7 0 ka the pedogenic carbonate zones were probably formed under warm and dry conditions the moderately weathered barton sand at the barton section and the equivalent sandy silt ii at other sections deposited between 92 7 0 and 69 6 4 ka suggest windy probably warm and fluctuating moisture consitions a reddish pedocomplex was formed from 70 to 35 ka under relatively warm and moist climatic conditions with a very low rate of loess deposition overlying the reddish pedocomplex is the sandy silt i probably a stratigraphic equivalent to the roxana silt dated at 40 30 ka in the central lowlands the gilman canyon formation 35 20 ka a thick cumulic loessial and organic matter rich pedocomplex developed under relatively moist and probably cool conditions the peoria loess was deposited at a very rapid rate under dry and cold conditions the brady soil 10 5 8 5 ka was formed under relatively warm and moist conditions the poorly weathered bignell loess was deposited during the warm and dry altithermal period 9 5 ka

comparing gravel bed rivers in paired urban and rural catchments of southeastern pennsylvania surveys in eight paired urban and rural watersheds illustrate how urbanization changes fluvial morphology and processes our data also provide quantitative criteria for evaluating streamrestoration projects in urban areas bankfull depth reach averaged bed slope and median grain size are similar in urban and rural watersheds the median width of urban channels is 26 larger than the median width of rural channels the median sinuosity is 8 lower in urban channels and pools are 31 shallower the median composite manning s n based on median grain diameter pool depth and channel sinuosity is 10 lower in urban streams while the median bankfull discharge per unit drainage basin area is 131 higher in urban channels histograms of bed sediment size distributions in urban channels lack a secondary mode in the size range 2 64 mm characteristic of rural channels indicating that these sizes tend to be selectively removed from urban channels however bankfull shields stresses in urban and rural channels exceed typical threshold values at most sites indicating significant bedload transport at bankfull stage apparently increased peak discharges caused by decades of urbanization have not removed all the transportable sediment from these urban stream channels we speculate that the supply of sediment to urban channels from hillslope processes and channel erosion remains significant even though much of the upland surfaces of these urban catchments are covered with nonerodible impervious surfaces

a correlation between earthquakes and eruptive phases at mt etna an example and past occurrences a local array was deployed on mt etna to follow precisely the seismic activity occurring at the end of the eruption of the southeast crater in october 1984 swarm activity at sea level beneath the summit was followed by isolated earthquakes a few kilometres deeper and more distant and eventually by destructive earthquakes on the lower slopes there was no continuous migration between these domains of eruptive and seismic activity but the time relation is striking a revised use of the exceptional record over four centuries of eruptions and destructive earthquakes in the mt etna region documents the statistical significance of this type of occurrence of major earthquakes in relation to the end of eruptions

character of the stress field in the calabrian arc and southern apennines italy as deduced by geological seismological and volcanological information abstract three crustal sections located in key zones of the calabrian arc and southern apennines have been drawn on the basis of the available geological geophysical seismological and volcanological data the purpose is to gather information on the state of stress at different crustal levels and to test to which extent data sampled at different time intervals may be consistently compared the analysis allows for the individualization of the following sectors 1 1 peri tyrrhenian belt marked by a tensional state of stress down to the moho depth 2 2 apenninic chain subjected to tension only in its shallow portions and to a compressive regime at depth 3 3 external chain internal foretrough characterized by a deep compressive regime which is expressed at the surface in its outermost zone only 4 4 external foretrough foreland with tensional processes in the whole crust compressional processes are linked to the activity of a deep shear zone which causes the thrusting of the tyrrhenian crust over the adriatic crust and which seems to control the present distortion of the calabrian arc the analysis suggests a change in the stress field and deformation mechanisms from the uppermost to the lowermost levels of the crust and an eastward migration with time of the compressional events these facts would explain the contrasting evidence sometimes given by stress constraints derived from geological seismological and volcanological data

comparison of epm and psiac models in gis for erosion and sediment yield assessment in a semi arid environment afzar catchment fars province iran abstract this research was conducted in the afzar sub catchment area of ghara aghaj river a semi arid region in sw iran using a geographic information system gis to compare the erosion potential method epm and pacific southwest interagency committee psiac models in erosion potential mapping and sediment yield assessment data layers used in this study were generated from topographic maps landsat etm imagery aerial photographs field surveys and barometric and pluviometric data factor class evaluation was used to determine epm and psiac parameters a raster based geographic information system gis was applied to generate the erosion severity and sediment yield maps output data was verified by field observation and by comparison with a global assessment of soil degradation glasod map comparison of the epm and psiac results with field observations and the glasod map showed that although the results of the two erosion potential maps correspond in most areas the results of epm model were not as reliable as the psiac in identifying areas with very high erosion potential it is suggested the epm model should be used for rapid mapping of erosion potential in regions with limited data layers but field verifications indicated that psiac results were the more reliable