subsurface hydrology of layered colluvium mantles in unchannelled valleys south eastern brazil the effects of subsurface hydrology on the evolution of erosive processes inside layered colluvium mantles in unchannelled valleys are investigated tensiometer nests are installed in different morphological conditions with their specific depths controlled by the subsurface structure of the colluvium mantle daily readings during one year and physical and mechanical analyses of the different colluvium layers are carried out in spite of a highly discontinuous subsurface structure present topography is the major factor controlling subsurface flow in this landscape paleotopographic features usually resulting from the lateral mobilization of the previous topographic hollow axis can locally control the preferential expansion of the saturated zone towards areas other than the present hollow axis during rainy periods pressure head at the base of the hollow axis increases towards a maximum value which is not increased by subsequent precipitation inputs new water input is dissipated by direct precipitation onto the saturated zone and exfiltration by seepage at the gully head walls precluding the development of the excess pore pressures required to trigger failure by landsliding

evaluation of sample quality of sensitive clay using intrinsic compression concept a simple index the degree of sample disturbance is proposed in this study to quantitatively evaluate the quality of sensitive clay samples based on the concept of void index proposed by burland in 1990 the degree of sample disturbance is defined as the ratio of the difference between the in situ void index and the void index of the undisturbed sample tested in the laboratory to the difference between the in situ void index and the void index of the completely remolded clay all these indices are determined at the same effective overburden stress theoretically the degree of sample disturbance varies from 0 perfect undisturbed sample to 100 completely remolded sample the proposed index is used in this study to evaluate the sensitive ariake clay in japan oedometer tests on undisturbed samples of natural ariake clay obtained from the field using the current sampling practice in japan show the degree of sample disturbance ranging from approximately 5 to 38 the clay sample with an in situ void index closer to the intrinsic compression line has a lower degree of sample disturbance in addition a series of consolidation and unconfined compression tests were conducted on artificially disturbed samples in the laboratory to demonstrate the change of consolidation yield stress unconfined compressive strength and compression index with the degree of sample disturbance a simple method is proposed in this paper to correct the mechanical parameters measured in a laboratory setting considering the degree of sample disturbance

intraseasonal oscillations in the global atmosphere part ii southern hemisphere abstract in part ii of this two part article we complete the systematic examination of oscillatory modes in the global atmosphere by studying 12 years of 500 mb geopotential heights in the southern hemisphere as in part i for the tropics and northern hemisphere extratropics the data were band pass filtered to focus on intraseasonal is phenomena and spatial eofs were obtained the leading principal components were subjected to singular spectrum analysis ssa in order to identify nonlinear is oscillations with high statistical confidence in the southern hemisphere the dominant mode has a period of 23 days with spatial patterns carried by the second and third winter eof of the is band it has a zonal wavenumber four structure the 40 day mode is second and dominated by wavenumbers three and four while a 16 day mode is too weak to separate its spatial behavior from the previous two the is dynamics in the southern hemisphere is more complex and dominated by shorter wavenumbers than the northern

episodic late quaternary palaeogully erosion in northern kwazulu natal south africa abstract hillslope deposits in northern kwazulu natal south africa are incised by gullies dongas which expose sequences of buried palaeosols developed within a succession of discontinuity bounded colluvial sedimentary units infilled and buried palaeogully topography attests to at least four geomorphic cycles comprising gully cut and fill and palaeosol formation on hillslopes in the region during the past 135 ka past attempts at dating colluvial stratigraphic units were limited to radiocarbon dating of associated palaeosol organic matter and authigenic soil carbonates this study presents a preliminary set of infra red stimulated luminescence irsl age determinations pertaining to deposition of the succession of colluvial units infilling and burying palaeogullies at several sites of stratigraphic geochronological and palaeoenvironmental importance in the region interpretation of the irsl and 14 c dates in the context of cyclical hillslope processes suggests that past episodes of palaeogully erosion and infill were not synchronous and individual palaeosol landsurfaces were diachronous during the late pleistocene

nature of environmental changes in south america at the last glacial maximum abstract a review is given of geomorphological evidence suggesting the nature of environmental changes in south america during the last glaciation maximum lgm the data are from glacial geocryogenic alluvial colluvial and aeolian systems and span 68 of latitude making the most complete land transect of major climatic systems in the southern hemisphere glaciers in the northern and central andes may have reached their maximal extent by 27 000 yr b p reduced precipitation at the lgm caused by lower temperatures and lower atmospheric humidity probably led to slight glacier recession in the tropical andes icefields in the southern andes were most expansive when global temperature and sea level were lowest because pacific westerlies supplied abundant moisture and western outlets advancing across the continental shelf were constrained by sea level low gradient river networks became incised by at least 100 m into narrow channels as global sea level fell by 120 m during the lgm draw down of water tables possibly impacted the forest cover enhancing the drying influence of reduced sea surface temperature and atmospheric humidity as forest and grass covers diminished in extent effecting greater atmospheric cooling because of reduced evapotranspiration and convective condensation colluvial and aeolian processes became more active and widespread almost 25 of the continent is covered with palaeo aeolian features presumed to have been active when airflow was stronger due to steeper atmospheric pressure and temperature gradients at the lgm substantial changes in precipitation totals and incidence and in ground water availability probably eliminated modern type tropical rainforest except in areas currently receiving ca 5000 mm of annual rainfall equivalent changes in vegetation cover spread across much of the guyana and brazilian highlands and throughout the southern temperate regions

state boundary surface for very loose sand and its practical implications a state boundary surface defines a boundary in stress void ratio space above which no stress state can exist the applicability of the state boundary surface for sand has not gained widespread attention primarily because sand is not generally considered to be a difficult soil from a design point of view apart from liquefaction liquefaction is a phenomenon usually encountered in very loose cohesionless materials an experimental study relating the drained and undrained behavior of very loose saturated sand is presented it is shown that the post peak portion of undrained stress paths travels along the state boundary and that the state boundary can be approximated by a straight line the slope of this straight line appears to stay constant for very loose sand there are potentially an infinite number of these lines which form a three dimensional surface in deviator stress effective mean normal stress void ratio space previously published results by various researchers are used to confirm the existe

analysis of hillslope erosion rates using dated colluvial deposits hollows are sites of long term deposition of colluvium and contain a valuable record of the timing and rates of hillslope erosion a model is presented that uses measured depositional rates of colluvium in hollows to calculate transport rates of colluvium and bedrock lowering rates on the surrounding slopes this model has been applied to eight dated colluvial deposits in the clearwater river basin of western washington the calculated average transport rate is about 34 cm 3 cm yr and the calculated average bedrock lowering rate is about 0 04 mm yr equivalent to an average sediment yield of 90 t km 2 yr for the holocene there is significant variability in erosion rates between sites which may be due to local lithologic variations although the average values are similar to an independent estimate of modern erosion rates for this area multiple stratigraphic levels have been dated in five deposits and document that the deposits are cumulative and that deposition has been active through the

study of the structure of a sensitive champlain clay and of its evolution during consolidation scanning electron microscopy and mercury intrusion porosimetry are used in parallel to identify the structure of a medium sensitivity champlain clay the clay structure is observed firstly on intact remolded and oven dried soils and secondly on soils consolidated at various levels in one dimensional compression both methods of investigation reveal for the intact soil the existence of an aggregated structure characterized by an interaggregate and an intra aggregate porosity remolding affects interaggregate links but does not destroy aggregates the observation of clay structure at various levels of one dimensional compression shows that the collapse of the structure is progressive the largest interaggregate pores being the first affected as the consolidation proceeds smaller and smaller pores are affected for a given pressure increment only the largest existing pores are affected a structure anisotropy has been seen to develop with increasing compression the scanning electron microscope and the me

global view of the intraseasonal oscillation during northern winter abstract in this study svd analysis is applied to a normalized 200 mb streamfunction olr covariance matrix to extract the most recurrent coupled pattern in the northern winter after the removal of the climatological seasonal cycle and seasonal means for each winter the first two singular vectors are on an intraseasonal timescale and the combination of the two forms an oscillation it is characterized by eastward propagation in the indian ocean and the western pacific standing oscillations in both the tropics and the extratropics and the poleward propagation of a zonally symmetric structure although there exists an eastwardly propagating pattern the phase relationship between geopotential wind and streamfunction fields is inconsistent with that of equatorial kelvin waves eastward propagation is most evident in the tropics of the southern hemisphere while the signals in the northern hemisphere are characterized by standing oscillations the distinct characteristics of the northern and southern he

paleoenvironmental dynamics of low order paleovalleys in the late quaternary palmas cacador summit surface southern brazil abstract the quaternary dynamics of landscapes in the subtropical continental region of brazil is not still well understood pedostratigraphic records of low order paleovalleys paleovalley heads and 1st and 2nd order paleovalleys of the palmas cacador summit surface serve as important resources for the identification of landscape component responses relief soil sediment and vegetation of plateau areas of southern brazil in the light of environmental changes driven by climatic variations of the late quaternary we integrated litho pedo allo and chronostratigraphic descriptions with carbon stable isotope analysis phytoliths indices and 14c and osl dating we found that at 44 86 ky bp there was a change in the hydrodynamics of 2nd order perennial channels humid climate controlled possibly by tectonics at 28 35 to 23 69 to 28 ky bp regressive pedogenesis in dry climate began with a predominance of erosion by overland flows at 2 60 to 23 69 ky bp full regressive pedogenesis occurred under a continuous climate regime of drier characteristics punctuated by millenary climatic fluctuations to a wetter regime of between 4 60 and 19 77 ky bp echoing the results postulated by the knox s model during this period the most pronounced modifications to the landscape were made with a change in vegetation from campo cerrado to campo limpo with changes in erosion patterns caused first by overland flows and then earthflows debris flows and with the gradual silting filling and burying of gullies valley heads and 1st and 2nd order valley bases since 2 60 ky bp the area returned to a predominance of progressive pedogenesis in wet and cold climates finally we found that at the local scale low order basins

an observational study of medium scale wave dynamics in the southern hemisphere summer part i wave structure and energetics abstract medium scale waves zonal wavenumbers 4 7 frequently dominate southern hemisphere sh summer midlatitude circulation patterns this work is an observational study that focuses on their temporal and spatial characteristics along with detailing the forcing mechanisms responsible for their formation medium scale wave characteristics for three sh summers 1978 79 through 1980 81 are discussed it is shown that the time mean medium scale wave structure is consistent with the basic state linear wave propagation characteristics the energetics of the medium scale waves are studied using the transformed eulerian mean formalism of plumb it is found that wave zonal mean exchange is a valid concept for describing the sh summer atmospheric circulation and that the flow vacillates between periods of highly perturbed and zonally symmetric states with a time wale on the order of 10 20 days these vacillations result from nonlinear baroclinic instabilities and the medium scale waves exhibit well defined

erosion disconformities and gully morphology a threedimensional approach abstract the results of a study of 106 recently formed gullies in bananal in the state of sao paulo brazil is applied in this paper to the analysis of paleogullies detected in the same region bananal is situated in a region where coffee was previously cultivated on the southeastern brazilian plateau the area is characterized by a hilly policonvex relief we observed that gullies tend to cut into hollows on the concave slopes as the slopes in this area were formed by several colluvial deposits setting discordantly we decided to specify the relations between slope geometry and erosion process by the analysis of a three dimensional representation of paleoslope geometry this approach should provide a better insight into the role of hollows and paleohollows in the location of gullies on the slope indeed we observed that gully erosion in the hollows is a common process throughout the upper quaternary of our region this process is in fact responsible for the greatly varying geometry of erosion disconformities between colluvial deposits the morphological patterns of these disconformities led us to associate them with the evolution patterns of active gullies found today in the region

application of wavelet transform to meteosat derived cold cloud index data over south america abstract cold cloud index cci data derived from meteosat infrared imagery are used to detect periodicities in convective activity in south america the generally used fourier transform ft cannot provide time localized information but gives information on the average periodicity of oscillations over the entire time domain as many events in the atmosphere are intermittent wavelet transform wt is used to identify periodic events in cci data first the morlet wt is applied to different combinations of time series data of known periodicities to demonstrate the advantage of wt over ft later it is applied to cci data over four 9 square areas between the latitudes 4 5 n and 31 5 s and longitudes 54 45 w near the equator periodic convective activities are observed to be more prominent in the boreal summer than in the austral summer between the latitudes 4 5 and 22 5 s 1 2 3 approximately 5 and 8 10 day oscillations are seen in the austral summer and seldom is any convective activity seen in

stratigraphy of near valley head quaternary deposits and evidence of climate driven slope channel processes in southern brazilian highlands abstract during the past 40 years colluvial and alluvial deposits have been used in brazil as good indicators of regional landscape sensitivity to quaternary environmental changes in spite of the low resolution of most of the continental sedimentary record geomorphology and sedimentology may favor palaeoenvironmental interpretation when supported by independent proxy data this paper presents results obtained from pedostratigraphic sequences in near valley head sites of southern brazilian highlands based on geomorphologic sedimentologic micromorphologic isotopic and palynologic data results point to environmental changes with ages that coincide with marine isotopic stages mis 5b 3 2 and 1 during the late pleistocene although under temperatures and precipitation lower than today the local record points to relatively wet local environments where shallow soil water saturated zones contributed to erosion and sedimentation during periods of climatic change as during the transition between mis 2 and mis 1 late pleistocene events with ages that coincide with the northern hemisphere younger dryas are also depicted during the mid holocene slope wash deposits suggest a climate drier than today probably under the influence of seasonally contrasted precipitation regimes the predominance of overland flow related sedimentary deposits suggests an excess of precipitation over evaporation that influenced local palaeohydrology this environmental condition seems to be recurrent and explains how slope morphology had influenced pedogenesis and sedimentation in the study area due to relative sensitiveness resilience and short source to sink sedimentary pathways near valley head sites deserve further attention in quaternary studies in the humid tropics

the 1985 86 intraseasonal oscillation and the role of the extratropics abstract an intraseasonal oscillation that occurred in the 1985 86 northern winter is documented in this study the tropical convection of this event is dominated by the mixture of a standing oscillation over the maritime continent and an eastward moving feature from the indian ocean into the central pacific the time evolution of the upper tropospheric circulation patterns instead of propagating eastward along the equator as suggested in the existing composites of the intraseasonal oscillation is characterized by a series of wave patterns in the northern hemisphere and does not complete the cycle around the globe the familiar moist kelvin wave explanation for the intraseasonal oscillation receives little support from diagnosis of this event using zonal wind height field streamfunction and potential vorticity only in the lower troposphere near the date line is the convincing evidence for its existence found a scenario for the intraseasonal oscillation which is suggested by the analysis includes

void fabric tensor and ultimate state surface of soils this paper presents a method to characterize the fabric of soils attention is focused on the directional distribution of voids in these materials the mean porosity and void fabric tensor used in the description are obtained by the stereological technique the use of a void fabric index to quantify the variation of the fabric tensor with deformation is highlighted the fabric description is also used to expand the critical state soil mechanics framework a proposal for an ultimate state surface of soils is made the study shows that the representation of the ultimate state surface is dependent on the choice of the set of pertinent state variables its representation in reduced state dimensions may not be unique the study further shows that the initiation of strain softening in soils is the result of structural collapse of the solid skeleton the use of the void fabric index to identify the initiation of collapse is explored

effects of tube sampling in soft clay a microstructural insight this paper analyses the effects of tube sampling in soft clay with particular emphasis on the modifications that occur in the clay fabric for tube specimens retrieved using open samplers shelby a

pore size distribution of a compacted silty soil after compaction saturation and loading soil microstructure is an important feature that controls soil behaviour at the macroscale this microstructure depends on the sample preparation method and evolves during saturation and loading this paper investigates the effects of compaction water content drying techniques adopted prior to performing porosimetry saturation and loading on the evolution of the microstructure of a silty soil mercury intrusion porosimetry is used to obtain the pore size distribution at different states of soil presenting single and double porosity it is observed that in presence of aggregates obtained from a compaction on the dry side of optimum the bimodal pore size distribution is not significantly affected by the saturation process at zero stress this feature of behaviour is quite specific to low plasticity silty soil conversely loading under saturated conditions has a more significant effect on the pore size distribution this bimodal distribution converges into a single mode of pore size when the stress is

microfabric analysis by manual and automated stereological procedures a methodological approach to antarctic tillite fabric analysis is commonly used to infer former movement directions of diamictons however analysis techniques are typically time consuming and partly subjective stereological analysis provides an alternative for objective determination of the preferred orientation of particles the ability of manual and automated stereological procedures to determine the preferred orientation of particles 120 4000 m in tillite is assessed using core samples from mount feather mcmurdo dry valleys antarctica orthogonal sets of vertical thin sections were subjected to directed secant analysis involving the determination of the number of intersections between particle outlines and a rotating series of parallel lines the manual analysis reveals a weakly developed three dimensional tilt angle plunge of 68 this reflects the depth averaged subglacial deformational structure of the deposit because the preferred orientation signal is weak in the automated set up this signal is obscured by the effect of digitization hampering the reliable assessment of the orientation direction the study shows microfabric variability within the studied cored section that is interpreted as a shear fabric reliable macrostructural information that might constrain ice flow directions requires a larger number of randomly or systematically drawn core samples from which averaged microstructural fabrics can be derived

evidence for lake formation as a response to an inferred holocene climatic transition in brazil abstract geochemical mineralogical and palynological records from a holocene sediment core 12 7 m long from lake silvana southeastern brazil served to identify the source of detrital sediments within catchment soils the lake basin was first flooded in the early holocene 9400 14 c yr b p when a gibbsite rich b soil horizon started to accumulate four distinct hydrologic phases are consistent with vegetational changes indicated by pollen data phases of slope instability colluviation and low lake level correspond to pollen free intervals and point to a severe retreat of the vegetation cover the rapid sedimentation of slope wash sediments alternating with alluvial sediments appears to have formed a tributary fan 7 8 m thick that dammed the lake silvana basin 8500 14 c yr b p probably as a response to a drastic increase in precipitation rates

patterns of development of lavaka madagascar s unusual gullies lavaka madagascar s abundant gullies show a complex pattern of development fourteen independent measures of size and shape in 93 lavaka were investigated by principal components analysis and discriminant function analysis typical lavaka start either as wounds and raw patches on mid hillside that develop step like head scarps or as toe slopes collapsed by seepage slumping or undercutting they become deep raw vertical sided teardrop to heart shaped gashes that may be deepest and broadest uphill as the walls retreat slump and become overgrown lavaka become longer broader gentler and partly filled concavities they can grow to reach from the valley floor to the hill crest or even beyond the crest before healing over unless excessive erosion creates tors and inselbergs they heal over and end up as unremarkable hillside reentrants and side valleys

geomorphic response to rapid climatic and hydrologic change during the late pleistocene and early holocene in the humid and sub humid tropics abstract the data base concerning late quaternary environmental change in the humid tropics is dependent on records from scattered sites the intensity and duration of wet dry oscillations remain speculative and the responses of hillslopes and river systems are based on over simplified models however available evidence indicates that prolonged aridity affected all but a few favoured core areas of equatorial climate after 20 000 bp lasting 5 7 ka dry conditions at the lgm were marked by semi arid landforms and reduced steam activity large palaeofloods occurred after 13 000 be but dry conditions returned after 11 000 bp before the early holocene pluvial led to abundant sedimentation lasting nearly 2 ka after 9500 bp in africa amazonia and australasia erosion channel cutting and flood deposition occurred at the pleistocene holocene transition followed by multiple shifts from lateral to vertical accretion fill cut episodes during the early holocene while thick overbank deposits formed during the later holocene re establishment of the lowland rainforests was delayed until after 9000 bp in africa australia and brazil and several wet dry oscillations followed in the mid holocene period hillslope activity at the lgm was marked by local sediment transfers and fan formation at the termination sediment fluxes increased rapidly but mass movement probably peaked after 10 000 bp sediment delivery to stream channels was not immediate and large sediment stores remain on the landscape today many in areas of potential sensitivity of erosion

controlling factors of gullying in the maracuja catchment southeastern brazil hundreds of gullies vocorocas of huge dimensions up to 400 500 m long 150 m wide and 50 m deep are very common in the small maracuja catchment in southeastern brazil these erosional features which occur with an uneven intensity throughout the area started due to bad soil management practices at the beginning of european settlement at the end of the 17th century and nowadays are still evolving but at a slower rate as surface soils are usually very resistant to erosion the outcrop of the more erodible basement saprolites seems to be an essential condition for their beginning an analysis of well known erosion controlling factors was performed aiming to explain the beginning and evolution of these gullies and to understand the reasons for their spatial distribution data shows that geology and mainly geomorphology are the main controlling factors since gullies tend to be concentrated in basement rock areas with lower relief domain 2 of maracuja catchment mainly at the fringes of broad and flat interfluves at the detailed scale 1 10 000 gullies are more common in amphitheatre like headwater hollows that frequently represent upper quaternary gullies paleogullies which demonstrate the recurrence of channel erosion so gullies occur in areas of thicker saprolites domain 2 in places with a natural concentration of surface and underground water hollows saprolites of the preserved non eroded hollows are usually pressurized confined aquifer due to a thick seal of quaternary clay layer in a similar configuration to the ones found in hollows of mass movement mudflow sites in southeastern brazil therefore the erosion of the resistant soils by human activities such as road cuts and trenches valos or their mobilization by mudflow movements seem to be likely mechanisms of gullying initiation afterwards gullies evolve by a combination of surface and underground processes such as wash and tunnel erosion and falls and slumps of gully walls copyright 2005 john wiley sons ltd

liquefaction and flow failure during earthquakes two aspects of seismically induced liquefaction are discussed which are of vital engineering significance the triggering condition and the consequences of liquefaction the triggering condition is examined with respect to liquefaction analysis note being taken of the onset condition which is governed by cyclic strength consequences of liquefaction are discussed with respect to post seismic stability analysis in which the residual strength plays a major role procedures used for liquefaction analysis based on the results of in situ sounding tests are introduced and the applicability of this method for estimating associated ground settlements is discussed the evaluation of residual strength requires a better understanding of undrained sand behaviour results of extensive laboratory rests on japanese standard sand are examined and new index parameters are proposed to quantify undrained sand behaviour better the results of laboratory tests on silty sands are examined in the same way ah the results are

observations of cloud cluster hierarchies over the tropical western pacific infrared radiance measurements at cloud top by the japanese geostationary meteorological satellite gms were used to study the structure and propagation of tropical convective systems over the equatorial western pacific results indicate that tropical convection in this region possesses three fundamental periodicities 1 day 2 3 days and 10 15 days cloud clusters within these convective systems interact to produce a hierarchy of collective motions covering all of these three basic time scales the 10 to 15 day time scale is closely related to the intraseasonal or 30 60 day oscillations that propagate from the indian ocean to the western pacific along the equator all year round large convective complexes known as supercloud clusters scc are found to organize in the 10 to 15 day time scale especially over the open warm water of the western central pacific 160 e to 180 the sccs generally propagate eastward although occasionally they can also propagate westward the zonal propagation can occur either continuously or intermittently in both cases the scc is found to be made up of several well organized cloud clusters which are generated at 2 to 3 day intervals and propagate in the opposite direction to the scc the diurnal variation is most pronounced over the maritime continent although significant amplitudes are also found over the open ocean the amplitude of the diurnal cycle is strongly modulated by the 2 to 3 day and 10 to 15 day oscillations advanced spectral analysis methods applied to convective indices derived from the radiance data confirm this hierarchical structure in cloud clusters in the tropical western pacific in addition to the embedding of well organized clusters within a scc in the spatial domain there is also a similar embedding by successive longer scales in the time domain interactions between the major frequency groups appear also to give rise to intermediate frequency variations a discussion of the present results in the context of equatorial wave dynamics of the moist tropical atmosphere is also presented