glacial and nonglacial sediment contributions to wisconsin episode loess in the central united states the relative contributions of various glacial and nonglacial sediments to wisconsin episode loess units along the lower illinois and central mississippi valleys are estimated on the basis of a comparison of magnetic susceptibility and silt and clay mineralogy a mathematical method of source area calculation using four compositional parameters was guided by current knowledge of the regional glacial history on the basis of this technique the roxana silt along the illinois and mississippi river valleys is composed of significant superior lobe sediment 35 40 as well as wadena or des moines lobe sediment about 35 this can account for its high magnetic susceptibility feldspar content kaolinite content and pink hue lower peoria silt contains about 25 35 lake michigan lobe sediment with reduced contributions of the other sources after the mississippi river s diversion 20 4 ka the supply of superior des moines and wadena lobe sediment was cut off from the illinois valley in favor of lake michigan lobe sediment 75 80 contribution this major source area shift accounts for higher dolomite and illite contents and a more yellow hue in approximately the upper two thirds of peoria silt in the study area in loess south of st louis less pronounced compositional shifts occur because superior lobe sediment was not cut off and because des moines lobe wadena lobe and missouri river sediments having more intermediate composition compose 40 50 of the loess thereby diluting other source area changes nonglacial sediment from fluvial and periglacial sources is estimated to compose 10 40 of loess in both regions

a flexural isostatic model of lithosphere shortening and foreland basin formation application to the eastern cordillera and subandean belt of nw argentina a numerical model of lithosphere shortening has been developed to combine flexural isostatic and structural balancing this allows us to quantitatively reconcile lithosphere shortening thrust sheet emplacement and foreland basin formation lithosphere shortening is accommodated by thrusting in the upper crust and by distributed deformation in the lower crust and the lithospheric mantle this leads to loading by thrust sheet emplacement crustal thickening and thermal perturbation additional loading and unloading are generated by sedimentation and erosion respectively the model is kinematically controlled each fault having its position geometry and movement prescribed the model is applied to the subandean late oligocene to recent foreland fold and thrust belt of nw argentina at 22 15 s the subandean belt of nw argentina contains three major stratigraphic units the lower middle and upper terciario subandino formations by modelling these formations we attempt to determine whether the terciario subandino group can be explained as a foredeep fill in response to thrust sheet loading and if so what is the required effective elastic thickness a successful model must predict not only foreland stratigraphy but also exhumation topography and crustal thickness we see a change in the wavelength of sedimentary deposition in the subandean basin through time that can be accounted for by a change in flexural rigidity accommodation space for the lower terciario subandino formation can be generated using an elastic thickness of 70 km for the middle upper terciario an elastic thickness of 15 km produces the correct basin geometries shortening estimates of 110 km have proved sufficient to generate the observed foreland stratigraphy bouguer anomaly and topography across the subandean belt and eastern cordillera however an additional 140 km of shortening is required to generate the observed bouguer anomaly and topography across the western andes this discrepancy could be due to earlier shortening in the western andes or to crustal thickening by magma addition

age of colluvium indicates accelerated late wisconsinan hillslope erosion in the upper mississippi valley colluvium on foot slopes in parts of north america and europe has been attributed to a major mass wasting episode during the last glacial period stratigraphic evidence and 14 c ages support this hypothesis for the northern part of the upper mississippi valley colluvium in this region grades laterally into or interfingers with fluvial sediment beneath the late wisconsinan savanna terrace colluvial foot slopes are truncated by fluvial surfaces postdating the incision that created the savanna terrace between 13 and 11 ka samples from within the colluvium have 14 c ages between 18 6 and 12 ka ages of 28 9 and 20 3 ka have been obtained from beneath colluvium and fluvial sediment inset into colluvial foot slopes has yielded ages between 12 5 and 9 8 ka widespread permafrost during the late wisconsinan glacial maximum may explain the onset of accelerated mass wasting that produced the colluvium although mass wasting apparently continued for some time during subsequent climatic warming the results described here imply major long term climatically driven fluctuations in sediment supply from hillslopes to the fluvial system in this region

loess mantle spatial variability and soil horizonation southern wisconsin usa abstract loess is an important quaternary sediment that records evidence of landscape instability in sediment source areas and landscape stability in accumulation areas in wisconsin usa loess mantles glaciogenic deposits dating to the last glaciation but the landscape distribution and effects of the loess mantle on soil formation have received very little attention this study investigates the influence of glacial landforms on the spatial pattern of loess thickness and how the presence or absence of a loess mantle overlying glaciogenic sediments has influenced soil profile morphology namely thickness and nature of horizonation loess thickness follows systematic trends along hillslopes with slope percentage explaining most loess thickness variation between summit and backslope positions in the presence of a loess mantle solum and bt horizon thickness is proportional to the thickness of the loess mantle in well drained profiles in the absence of a loess mantle landscape and sediment characteristics that control permeability and water throughflow appear to be the most important determinants of profile characteristics the loess mantle modulates soil formation above the lithologic discontinuity with sandy calcareous glacial sediments by controlling soil water behavior and having physical and chemical characteristics conducive to transformation to soil genetic horizons

landscape evolution alluvial architecture environmental history and the archaeological record of the upper mississippi river valley abstract the alluvial fill in the upper mississippi river valley umv is a palimpsest of past landscapes environments and physical evidence of human life ways the valley has undergone significant changes in fluvial style during the time humans have occupied its landscapes including changes in channel pattern location of depocenters and sediment lithology remnants of late glacial braidplains that predate human presence in the upper midwest occur as sandy terraces and terrace fills a subsequent major change in alluvial architecture resulted from fundamental changes in seasonal water and sediment input that marked the end of glacial meltwater input into the valley about 12 4 ka 10 500 14c yr b p a shift to net transport of sandy bedload and storage of fine grained overbank sediment on the floodplain accompanied the change to an island braided channel pattern at that time the holocene channel belt has been significantly narrower and the zone of sediment storage is reduced relative to that of the late glacial river major holocene depocenters include alluvial fans and colluvial slopes floodbasins natural levees and fluvial fans at the junction of large tributaries climate models and paleobotanical and isotopic studies indicate that shifts in large scale patterns of atmospheric circulation and moisture transport into the mid continent of north america induced hydrologic and vegetation changes that strongly influenced flood frequency and magnitude the delivery of sediment from tributary basins and the evolution of the umv landscape understanding the alluvial architecture of the valley and the temporal spatial distribution of biotic environments and processes that have buried mixed altered or destroyed archaeological deposits is essential to develop strategies for sampling the valley for evidence of past human activity and for properly interpreting the archaeological record

a new model of topographic effects on the distribution of loess a model of topographic influence on the regional transport and accumulation of loess in sparsely vegetated landscapes is proposed based on the critical role played by saltating eolian sand in the entrainment and long distance transport of finer grained suspended dust in this model long term accumulation of loess occurs mainly downwind of topographic obstacles that limit eolian transport of sand and associated re entrainment of dust regional and local patterns of distribution of late wisconsinan loess in parts of the upper mississippi river basin are closely related to the distribution of topographic obstacles to sand transport these cases of topographic influence occur in a region where evidence exists for sparse tundra like vegetation during the deposition of loess in the late wisconsinan similar topographic effects may not be evident further south in the missouri and mississippi river basins because vegetation density was generally sufficient to prevent the movement of eolian sand out of source valleys thus topographic obstacles and dense vegetation may have similar effects on loess distribution under different environmental conditions

optical ages on loess derived from outwash surfaces constrain the advance of the laurentide ice sheet out of the lake superior basin usa abstract we present textural and thickness data on loess from 125 upland sites in west central wisconsin which confirm that most of this loess was derived from the sandy outwash surfaces of the chippewa river and its tributaries which drained the chippewa lobe of the laurentide front during the wisconsin glaciation mis 2 on bedrock uplands southeast of the widest outwash surfaces in the chippewa river valley this loess attains thicknesses 5 m osl ages on this loess constrain the advance of the laurentide ice from the lake superior basin and into west central wisconsin at which time its meltwater started flowing down the chippewa drainage the oldest mar osl age 23 8 ka from basal loess on bedrock agrees with the established but otherwise weakly constrained regional glacial chronology basal ages from four other sites range from 13 2 to 18 5 ka pointing to the likelihood that these sites remained geomorphically unstable and did not accumulate loess until considerably later in the loess depositional interval other osl ages from this loess taken higher in the stratigraphic column but below the depth of pedoturbation range to nearly 13 ka suggesting that the chippewa river valley may have remained a loess source for several millennia

variations of elastic plate thickness at continental thrust belts after examining 15 reliable estimates of the elastic thickness of the lithosphere where it underthrusts mountain belts in europe asia and the americas we conclude that the strength of continental lithosphere as a function of depth must be very different from that of oceanic lithosphere depending on the state of stress continental lithosphere may be either very much stronger or very much weaker than would be predicted for oceanic lithosphere of the same thermal age we explain this observation as the result of two competing effects a thicker thermal plate beneath the continents which allows a deeper elastic ductile transition for plates more than 100 million years old and a low activation energy for ductile creep in the continental crust which leads to massive failure of the upper elastic lithosphere at high bending stresses the 100 km values for elastic plate thickness of billion year old lithosphere require a thermal plate thickness of at least 250 km the magnitude of apparent thinning of the elastic plate at high stress is consistent with that calculated from a simple yield envelope which includes a ductile zone in the lower crust the low yield strength of continental materials leads to correlations between effective elastic plate thickness and all of the following dip of the underthrust plate radius of curvature of the thrust front in map view and total length of the mountain belt using insight derived from laboratory experiments on the buckling of spherical shells and drawing analogies with the geophysical characteristics of oceanic subduction zones we arrive at the following sequence of causes and effects the primary variable is the dip of the downgoing plate presumably prescribed by its own excess mass and pressure exerted by dynamic flow in the mantle where this dip is steep the rigidity of the plate is weakened due to inelastic yielding the weakened plate can then buckle at small wavelengths into short arcuate mountain belts thus we believe that the mantle ultimately controls the pattern of surface tectonics but that the nonelastic rheology of the lithosphere is the mechanism by which that control is imposed

geospatial technologies and digital geomorphological mapping concepts issues and research geomorphological mapping plays an essential role in understanding earth surface processes geochronology natural resources natural hazards and landscape evolution it involves the partitioning of the terrain into conceptual spatial entities based upon criteria that include morphology form genetics process composition and structure chronology environmental system associations land cover soils ecology as well as spatial topological relationships of surface features landforms historically the power of human visualization was primarily relied upon for analysis introducing subjectivity and biases with respect to selection of criteria for terrain segmentation and placement of boundaries this paper reviews new spatio temporal data and geocomputational approaches that now permit earth scientists to go far beyond traditional mapping permitting quantitative characterization of landscape morphology and the integration of varied landscape thematic information numerous conceptual theoretical and information technology issues are at the heart of digital geomorphological mapping dgm and scientific progress has not kept pace with new and rapidly evolving geospatial technologies consequently new capabilities exist but numerous issues have not been adequately addressed therefore this paper discusses conceptual foundations and illustrates how geomorphometry and mapping approaches can be used to produce geomorphological information related to the land surface and landforms process rates process form relationships and geomorphic systems

distribution of silty mantles in soils of the northcentral appalachians usa abstract across the northcentral appalachians usa high silt content soils are found as silty mantles or deep high silt content pedons the origin of such soils can be attributed to additions of wind blown dust deposits wbd or local parent materials i e shales or siltstone lithology previous research on silt soils originating specifically from wbd attributed to late marine isotope stage mis 2 loess has often been isolated to drainageways receiving outwash from deglaciation we hypothesize that thin

ancient hillslope deposits missing links in the study of climate controls on sedimentation rare outcrops of miocene pliocene buried hillslopes and colluvium present in proximal basin fill exposures in the arid southwestern united states in settings free of tectonic influences reveal hillslope sediment production and delivery to piedmonts that vary as a function of climate change a petrologic weathering index for sand clay mineral data and stratigraphic relations indicates that episodes of greater production and delivery of colluvium from hillslopes coincide with more intense chemical weathering and thus greater effective moisture strata recording limited colluviation less intense weathering and piedmonts dominated by eolian processes very likely correspond to drier conditions the mode of climate driven hillslope and piedmont landscape responses evident in these older stratigraphic records corroborates the conceptual model developed by quaternary researchers for arid environments even though climate change was operating at higher amplitudes and different frequencies in the quaternary this evidence of long term continuity in the mode of landscape response to climate change provides a new level of support for using the geologic record to understand the effects of future climate change

autogenic incision and terrace formation resulting from abrupt late glacial base level fall lower chippewa river wisconsin usa abstract a paucity of research exists regarding the millennial scale response of inland alluvial streams to abrupt base level fall studies of modern systems indicate that over short time scales the response is a diffusion like process of upstream propagating incision in contrast evidence from the lower chippewa river lcr located in the upper midwest of the usa suggests that autogenic controls operating over time scales of several millennia can overwhelm diffusion resulting in incision that is prolonged and episodic during the last glacial maximum the lcr drained the chippewa lobe of the laurentide ice sheet to the glacial upper mississippi river umr as a meltwater stream it aggraded and filled its valley with glacial outwash as did its largest tributaries which were also meltwater streams its nonglacial tributaries aggraded too filling their valleys with locally derived sediment during deglaciation the umr incised at least twice abruptly lowering the lcr s base level 15 m at 16 ka or earlier and an additional 40 m at ca 13 4 ka each of these base level falls initiated incision of the lcr led by upstream migrating knickpoints the propagation of incision has however been a lengthy process the optically stimulated luminescence osl ages of terrace alluvium indicate that by 13 5 ka incision had advanced up the lcr only 15 km and by 9 ka only 55 km the process has also been episodic resulting in the formation of fill cut terraces inferred from gpr surveys and exposures of terrace alluvium that are younger and more numerous in the upstream direction autogenic increases in sediment load and autogenic bed armoring the result of periodic tributary stream rejuvenation and preferential winnowing of fines by the incising river may have periodically caused knickpoint migration and incision to slow and possibly stop allowing lateral erosion and floodplain formation to dominate a decline in sediment flux from stabilizing incised tributary stream systems would have led to renewed knickpoint migration and incision when floods of sufficient magnitude to breach the channel armor occurred minimal floodplain development along the upper section of the present day lcr along with the channel morphology of an unstable wandering gravel bed river immediately downstream from it suggest that the river is still responding to the base level falls that happened many millennia ago the autogenic controls on the lcr s response to umr incision are a direct consequence of the thick fills of noncohesive sediment that accumulated in its valley and the valleys of its tributary streams during the late wisconsinan making the lcr a prime example of a former proglacial river that remains a paraglacial fluvial system

modeling the evolution of the guadalquivir foreland basin southern spain 1 previous quantitative studies dealing with the origin of foreland basins have focused primarily either on the rheological basis of the lithosphere mechanical response or on the relationship between orogenic loading and sediment geometry to link the evolution of the guadalquivir foreland basin south iberia with the thermomechanical stratification of the iberian lithosphere we combine quantitative approaches to deep and shallow processes thrust loading lithospheric flexure thickness changes of the crust and the lithospheric mantle and surface mass transport a planform flexural analysis of the present day load distribution shows that basement subsidence is related not only to upper crustal thrusting but also to a deep seated additional load on the basis of the observed gravity and geoid fields we propose this additional load to be related to a lithospheric mantle thickening larger than the coeval crustal thickening further modeling of the evolution of a basin cross section reveals that the architecture of the sedimentary basin is additionally related to the lithosphere rheological response the quantitative study of the evolution of basement faulting and the forebulge uplift of sierra morena leads us to conclude that viscous stress relaxation and or plastic yielding within the lithosphere are key processes to explain the flexural evolution of the basin

glacial interglacial variation in denudation rates from interior texas usa established with cosmogenic nuclides abstract the brazos colorado and trinity rivers of texas drain a tectonically quiescent non glaciated and low relief landscape inland from the gulf of mexico where long term 10 3 10 5 a changes in denudation rates are probably driven largely by climate change here we use cosmogenic 10be to obtain spatially averaged denudation rates for these river catchments primarily from terrace deposits associated with glacial or interglacial intervals over the past half million years the denudation rates are 30 35 higher during interglacial periods than during glacial periods and correlate broadly with temperature the results are consistent with predictions from the bqart sediment flux model and support the hypothesis that increased weathering rates associated with warmer climates will accelerate landscape erosion furthermore by analyzing 26al 10be in these deposits we can estimate the bed load sourced from up catchment surfaces the stored coastal plain fraction varies from 10 to 30 and is greater during times of relatively lower sea level the results indicate that although sediment flux is moderated by coastal plain storage increased up catchment flux during warmer interglacial periods outpaces evacuation of stored sediment during glacial periods resulting in a net increase in sediment flux to the ocean during warm intervals if this temperature sediment flux relationship is valid beyond the plio pleistocene transition then global sediment flux to the ocean from passive non glaciated and low relief landscapes would have been greater during the pliocene than in the cooler quaternary

petaloid organs preserved in an arctic plant macrofossil assemblage from full glacial sediments in southeastern minnesota abstract a small suite of plant macrofossils indicates that southeastern minnesota supported subarctic to arctic vegetation 18 700 yr b p fossil tepals of polygonum viviparum are exceptionally well preserved they occur with more fragmentary remains of dryas integrifolia vaccinium uliginosum var alpinum and probable species of arctic salix s cf herbacea and s cf arctica the pollen spectrum from this site is dominated by picea pinus and cyperaceae which are typical of midwestern full glacial sequences tundra like conditions with permafrost were present in southeastern minnesota during full glacial time local environments 18 700 yr b p reconstructed from both physical and paleobotanical evidence include wind swept ridge tops with thin loess outcrops of dolostone and sandstone on valley walls colluvial slopes sandy to gravelly floodplains shallow floodplain pools wet meadows and peaty turfs all in a treeless or nearly treeless environment

seismic crustal structure in the southwest of the iberian peninsula and the gulf of cadiz abstract the crust under the southwestern iberian peninsula and the gulf of cadiz has been sampled by 1200 km of deep seismic refraction wide angle reflection profiles together with many seismic reflection lines and bore holes wide angle seismic data were collected during the last three decades commercial multichannel data provide a detailed image of the uppermost crust improving the confidence about the models of the deeper structures p wave velocities within the thick column of sediments in the gulf of cadiz range from 2 0 to 3 8 km s while the algarve and the sines areas have higher velocities of 4 3 to 4 8 km s the top of the palaeozoic basement rises to the northwest outcropping in the south portuguese zone of the iberian massif and is characterized by p wave velocities of 5 7 5 9 km s high velocities of 6 4 km s have been found at shallow depths of 7 to 10 km in the south portuguese zone that could be related to the mafic and ultramafic rocks in the beja acebuches zone lower crustal velocities are in the range of 6 7 6 9 km s the crustal thickness shows important lateral changes from 29 km beneath the guadalquivir basin iberian massif contact to 35 km in the southeastern part of the south portuguese zone from the interpretation of these seismic data a geodynamic model of the evolution of the crust in southwestern iberia and the gulf of cadiz is proposed the guadalquivir basin and its continuation at sea the gulf of cadiz is a flexure area of the crust that could be related to the overloading due to the overthrusting of the alboran domain over the iberian plate

origin of the western subbetic arc south spain palaeomagnetic and structural evidence abstract an integrated structural and palaeomagnetic study in late cretaceous eocene rocks of the western subbetic arc in the betic cordillera of southern spain shows that the change in fold trend around the arc is significantly greater than the variation in primary magnetic declination this suggests that the arcuate geometry is not primarily a consequence of differential rotation the area has experienced a regional clockwise rotation of at least 40 which was most probably imposed during oblique wnw directed convergence along the southern iberian margin in early miocene time before the arcuate structure was formed kinematic indicators associated with the arcuate folds and thrust traces arc for the most part consistently wnw directed suggesting that the arc is not primarily a result of variations in the direction of tectonic transport the arcuate structure was probably initiated without significant rotation by the wnw directed indentation of the curved western end of the alboran domain into the iberian margin and was then tightened involving up to about 35 of further rotation in different segments of the arc finally one sector in the arc was rotated anticlockwise by about 40 with respect to the rest of the region reorientating the magnetic declinations the fold trends and the kinematic indicators this rotation was associated with local sinistral shear

catastrophic flooding from glacial lake wisconsin abstract glacial lake wisconsin was a large proglacial lake that formed along the southern margin of the laurentide ice sheet during the wisconsin glaciation it was formed when ice of the green bay lobe came into contact with the baraboo hills in southwestern wisconsin and blocked the south flowing wisconsin river during early glacial recession the ice dam failed catastrophically and the lake drained in about a week despite early recognition of the former lake and the likelihood that it failed catastrophically outflow rates during the failure have not been previously evaluated estimates based on step backwater modeling indicate that peak discharge was between 3 6 and 5 3 10 4 m 3 s in the lower wisconsin river as an alternate method we used a previously derived empirical relationship between lake volume and peak discharge for dam break events from a digital elevation model altered to incorporate isostatic depression we estimated the lake volume to be 87 km 3 just prior to dam breach suggesting that the flooding magnitude was as high as 1 5 10 5 m 3 s at the outlet adjusting these results for downstream flood wave attenuation gives a discharge of around 4 4 10 4 m 3 s in the lower reach which closely matches the results of the step backwater modeling these estimates of discharge from the catastrophic failure of ice marginal lakes improve our understanding of the processes that have produced the morphology and behavior of present day upper midwest river systems

mid crustal detachment in the betic system of southeast spain abstract the tertiary orogenic belts of eastern spain can be interpreted using the principles of thin skinned thrusting with a fundamental detachment at mid crustal level in the eastern betics the compression involves an oblique restacking of a stretched continental margin much of the shortening is transmitted on permian and triassic detachments which emerge as forward and back thrust duplexes an interpretation of the guadarrama range of central spain is presented in which significant shortening is shown on a mid crustal detachment propagating from the southeast it is suggested that this represents the external limit of a compressive system linked to the betics the pyrenees and eastern cantabrians are a separate tertiary compressive system again resulting from restacking of an extensional basin during the collision of iberia and france previous authors have proposed mid crustal detachment in the pyrenees observation of the geological map of the iberian ranges suggests a broadly similar structural origin may apply in which case the iberian ranges may represent the most external zone of a major pyrenean system again linked by a mid crustal detachment thus it is suggested that the whole of eastern spain is made up of two major compressive systems linked at mid crustal level

floodplain sedimentation in the upper mississippi valley natural versus human accelerated abstract understanding the time scales and pathways for response and recovery of rivers and floodplains to episodic changes in erosion and sedimentation has been a long standing issue in fluvial geomorphology floodplains are an important component of watershed systems because they affect downstream storage and delivery of overbank flood waters and they also serve as sources and temporary sinks for sediments and toxic substances delivered by river systems here 14c and 137cs isotopic dating methods are used along with ages of culturally related phenomena associated with mining and agriculture to determine rates of sedimentation and morphologic change for a reach of the upper mississippi river and adjacent tributaries in southwestern wisconsin and northwestern illinois the most important environmental change that influenced fluvial activity in this region during last 10 000 years involved the conversion of a late holocene mosaic of prairie and forest to a landscape dominated by cropland and pastureland associated with euro american settlement results presented herein for the upper mississippi valley umv show that the shift from pre agriculture natural land cover to landscape dominance by agricultural land use of the last 175 200 years typically increased rates and magnitudes of floodplain sedimentation by at least an order of magnitude accelerated overbank flooding led to increased bank heights on tributary streams and in turn contributed to more frequent deep flows of high energy these high energy flows subsequently promoted bank erosion and lateral channel migration and the formation of a historical meander belt whose alluvial surface constitutes a new historical floodplain inset against the earlier historical floodplain the new historical floodplain serves as a flume like channel that provides efficient downstream transport of water and sediment associated with moderate and large magnitude floods floodplains on lower tributaries however continue to experience rates of overbank sedimentation that are of anomalously high magnitude given improved land cover and land conservation since about 1950 this lower valley anomaly is explained by minimal development of historical agriculture period meander belts because of relatively low stream power in these channel and floodplain reaches of relatively low gradient in general long term pre agriculture rates of vertical accretion between about 10 000 and 200 years ago averaged about 0 2 mm yr 1 in tributary watersheds smaller than about 700 km2 and about 0 9 mm yr 1 on the floodplain of the upper mississippi river where the contributing watershed area increases to about 170 000 km2 on the other hand rates of historical vertical accretion during the period of agricultural dominance of the last 200 years average between 2 and 20 mm yr 1 with short episodes of even higher rates during times of particularly poor land conservation practices significant hydrologic effects of mining and agricultural started by the 1820s and became widespread in the study region by the mid 19th century the hydrologic and geomorphic influences of mining were relatively minor compared to those related to agriculture high resolution dating of floodplain vertical accretion deposits shows that large floods have frequently provided major increments of sedimentation on floodplains of tributaries and the main valley upper mississippi river the relative importance of large floods as contributors to floodplain vertical accretion is noteworthy because global atmospheric circulation models indicate that the main channel upper mississippi river should experience increased frequencies of extreme hydrologic events including large floods with anticipated continued global warming instrumental and stratigraphic records show that coincident with global warming a shift to more frequent large floods occurred since 1950 on the upper mississippi river and these floods generally contributed high magnitudes of floodplain sedimentation

last glacial loess in the conterminous usa the conterminous united states contains an extensive and generally well studied record of last glacial loess the loess occurs in diverse physiographic provinces and under a wide range of climatic and ecological conditions both glacial and non glacial loess sources are present and many properties of the loess vary systematically with distance from loess sources united states midcontinent last glacial loess is probably the thickest in the world and our calculated mass accumulation rates mars are as high as 17 500 g m 2 yr at the bignell hill locality in nebraska and many near source localities have mars greater than 1500 g m 2 yr these mars are high relative to rates calculated in other loess provinces around the world recent models of last glacial dust sources fail to predict the extent and magnitude of dust flux from the mid continent of the united states a better understanding of linkages between climate ice sheet behaviour routing of glacial meltwater land surface processes beyond the ice margin and vegetation is needed to improve the predictive capabilities of models simulating dust flux from this region r 2003 elsevier ltd all rights reserved

comment on alternating contractional and extensional events in the alpujarride nappes of the alboran domain betics gibraltar arc by juan c balanya et al

lithospheric folding in iberia integration of stress indicator data gravity data crustal kinematics data and analysis of topography and recent vertical motions demonstrates the occurrence of consistently oriented spatial patterns of large scale alpine to recent intraplate deformation in iberia the inferred upper crustal and lithospheric deformation patterns and the timing of the associated expressions at or near the surface support the existence of a close coupling with plate boundary processes operating at the margins of iberia patterns of lithosphere and upper crustal folds are oriented perpendicular to the main axis of present day intraplate compression in iberia inferred from structural analysis of stress indicator data and focal mechanism solutions these findings suggest the presence of lithospheric folds with wavelengths compatible with theoretical predictions of folding wavelengths of variscan lithosphere stress induced intraplate deformation set up by plate interactions is compatible with indications for the absence of present day deep mantle lithosphere interactions inferred from seismic tomography

simulation of shoreline change using airsar and polsar c band data this paper presents a new approach for modeling shoreline change due to wave energy effects from remotely sensed data the airborne airsar and polsar data were employed to extract wave spectra information and integrate them with historical remotely sensed data such as aerial photography data to model the rate of change of the shoreline a partial differential equation pde of the wave conversion model was applied to investigate the wave refraction patterns the volume of sediment transport at several locations was estimated based on the wave refraction patterns the shoreline change model developed was designed to cover a 14 km stretch of shoreline of kuala terengganu in peninsular malaysia the model utilized data from aerial photographs airsar polsar ers 2 and in situ wave data the results show that the shoreline rate of change modeled from the quasi linear wave spectra algorithm has a significant relationship with one estimated from historical vector layers of aerial photography airsar and polsar data with the quasi linear algorithm an error of 0 18 m year in shoreline rate of change determination was obtained with c vv band

parent material influence on soil response to vegetation change southeastern minnesota u s a abstract soil morphology changes dramatically across the former transition from forest to grassland in the midwestern u s a that vegetation boundary shifted as a result of holocene climatic change and fire suppression following euroamerican settlement but the timescale of soil response to those vegetation changes and the factors that influence it are poorly known on steep colluvial slopes of southeastern minnesota mollisols with thick dark a horizons typically associated with grassland are found today under deciduous forest soils with much thinner and or lighter colored a horizons occur immediately up and downslope of the forest covered mollisols most of the soils with thick a horizons are not in topographic settings found to favor organic matter accumulation in other landscapes principal component analysis highlights important axes of textural and mineralogical variation among horizons of these soils often related to parent material properties soils with and without thick a horizons are separated along one principal component heavily loaded by high ph reflecting the presence of dolomite fragments in the hillslope sediment that soils with thick dark a horizons formed in stable c isotope analysis reveals that the mollisols with thick dark a horizons under forest had c input from vegetation with abundant c4 grasses in the past public land survey data also indicate replacement of grassland or savanna by forest since 1854 on colluvial slopes where forest covered mollisols occur today we propose that the soils with thick dark a horizons under forest today reflect a lagged response to vegetation change from grassland or savanna to closed forest their thick a horizons and some c4 derived organic matter may be preserved because dolomite weathering releases abundant ca and mg that favor aggregation and organic matter stabilization soils with thin a horizons just up or downslope may also have formed partly under grasses but have responded more quickly and or more substantially to vegetation change

the topsar interferometric radar topographic mapping instrument the authors have augmented the nasa dc 8 airsar instrument with a pair of c band antennas displaced across track to form an interferometer sensitive to topographic variations of the earth s surface during the 1991 dc 8 flight campaign data were acquired over several sites in the us and europe and topographic maps were produced from several of these flight lines analysis of the results indicate that statistical errors are in the 2 4 m range while systematic effects due to aircraft motion are in the 10 20 m range the initial results from development of a second generation processor show that aircraft motion compensation algorithms reduce the systematic variations to 2 m while the statistical errors are reduced to 2 3 m

evidence for bioturbation of luminescence signals in eolian sand on upland ridgetops southeastern minnesota usa abstract this study sought to identify the age of eolian sand on narrow ridges in the root river valley of southeastern minnesota the ridges in the region are cored by ordovician dolomite and cambrian sandstone but the ridge tops are typically covered with late wisconsin peoria and older loess units in some locations peoria loess is absent and the ridgetops are covered with up to 3 m of eolian sand that was likely sourced from local river valleys and transported to the uplands by sand ramps we studied nine ridgetop soil profiles and collected seventeen osl samples from eolian sand at depths ranging from 0 3 to 2 6 m below the present ground surface all osl samples were analysed using small aliquots where 90 150 m quartz grains were applied to the inner 2 mm of 10 mm aluminum disks the osl ages ranged from 12 3 to 1 5 ka indicating a significant amount of age variability and potentially suggesting nearly continual eolian deposition throughout the holocene however several key differences were identified between those samples taken from within 1 m of the ground surface compared with samples that were more deeply buried those samples collected from depths of greater than 1 m yielded ages that were tightly clustered between 12 3 and 10 3 ka while samples taken from depths of less than 1 m showed ages with much higher spread that ranged from 1 5 to 10 1 ka the samples collected from within 1 m of the present ground surface also commonly showed higher spread in their equivalent dose distributions and higher overdispersion values relative to the samples that were more deeply buried this suggests the luminescence signals from the upper portions of these deposits were reset after burial most likely by bioturbation and that the osl ages are not depositional ages this interpretation is supported by evidence from a core sample collected from one of our sites that shows primary eolian lamina are preserved below 1 4 m depth but not above this depth presumably the bioturbation agents were effective at both resetting the luminescence signal and disturbing the primary bedding to depths of at least 1 m if bioturbation occurred below this threshold it apparently did not impact either of these indicators our findings suggest the upper 1 m of these profiles were impacted by bioturbation and that all of the eolian sand on these ridgetops was likely deposited prior to 10 1 ka

up in the refrigerator geomorphic response to periglacial environments in the upper mississippi river basin usa abstract james c knox was best known for his work on holocene and historical changes in fluvial systems but he also had a long standing interest in the effects of late pleistocene periglacial environments on landscape evolution in parts of the upper mississippi river basin that were just outside the laurentide ice sheet margin or as knox put it up in the refrigerator knox and others in the quaternary community of the midwestern u s often suggested that hillslope erosion was accelerated under periglacial conditions so that glacial periods have had a dominant effect on the landscape we see today this paper reviews the evidence and reasoning supporting that view in a study area of the upper mississippi basin bordered on three sides by ice margins of the last glaciation including the wisconsin driftless area and adjacent landscapes sparse but compelling paleoecological data and relict ice or sand wedge polygons provide clear evidence for a cold climate and widespread permafrost around the peak of the last glaciation in highly dissected relatively high relief parts of the study area the loess and soil stratigraphy on ridgetops and the colluvial mantles on steeper slopes are best explained by highly effective hillslope erosion including solifluction during and just after the last glacial maximum knox used the post depositional truncation of a loess unit to quantify contrasting late pleistocene and holocene sediment yields from a small driftless area watershed while the late pleistocene yield indicates accelerated erosion it is still lower than modern sediment yields in many tectonically active or semiarid landscapes and it may reflect deposition of highly erodible loess as well as effects of periglacial conditions the views of knox and other midwestern geomorphologists on landscape evolution through glacial interglacial cycles were highly influenced by the work of robert v ruhe ruhe proposed that an episode of widespread erosion during and just after the last glacial maximum can explain enigmatic aspects of quaternary stratigraphy and the soil landscape on the iowan erosion surface a very low relief landscape of the study area ruhe s key evidence is still valid though it needs to be separated from an implausible model of landscape evolution interpretation of the iowan erosion surface and other low relief landscapes just outside the ice margin also requires recognition of the profound effect of eolian processes on those landscapes under periglacial conditions many new insights on landscape evolution in the study area could result from wider application of cosmogenic nuclide based methods to assess glacial interglacial changes in basinwide rates of erosion and residence time of soils just as important a need exists for much more field based characterization of hillslope fluvial and eolian sediments for comparison with those of modern permafrost regions and past periglacial environments in europe

late quaternary loess landscape evolution on an active tectonic margin charwell basin south island new zealand abstract loess deposits constitute an important archive of aeolian deposition reflecting wider patterns of glacial atmospheric circulation and more localised interactions between riverine source areas loess trapping efficiency and geomorphic controls on erosion rate conceptual models have been formulated to explain the coeval evolution of loess mantles and associated landscapes loess landscape models but none apply to areas of tectonically induced base level lowering this study uses an age sequence of alluvial fill terraces in the charwell basin north eastern south island new zealand which straddles the transpressive hope fault to investigate geomorphic controls on loess landscape evolution in an active tectonic region we hypothesize that the more evolved drainage networks on older terraces will more effectively propagate base level lowering by way of a greater areal proportion of steep and convex hillslopes and a smaller proportion of non eroding interfluves eventually as the proportion of interfluves diminishes and hillslope convexity increases terraces shift from being net loess accumulators to areas of net loess erosion we investigate the nature of erosion and the geomorphic thresholds associated with this transition morphometric analysis of alluvial terraces and terrace remnants of increasing age demonstrated geomorphic evolution through time with a decrease in extent of original planar terrace tread morphology and an increase in frequency of steeper slopes and convexo concave land elements the number of loess sheets and the thickness of loess increased across the three youngest terraces the next oldest ca 150 ka terrace remnant had the greatest maximum number of loess sheets 3 and loess thickness 8 m but the loess mantle was highly variable a detailed loess stratigraphic analysis and the morphometric analysis place this terrace in a transition between dominantly planar uniformly loess mantled landforms and loess free ridge and valley terrain exemplified by the oldest terrace remnant variations in thickness and preservation of loess sheets demonstrated spatially and temporally variable erosion during loess accumulation to test our hypothesis of loess persistence we calculated critical steady state hillslope curvatures from a soil transport model calibrated for the study area above which the uppermost loess sheet l1 max thickness 1 8 m should be completely eroded we compared loess distribution mapped in the field to values of slope curvature calculated from topographic surveys and found two of three critical curvature values had acceptable predictive ability where predictions failed this is probably due to transient responses related to active steam incision because all critical curvature values predicted presence of loess on the oldest terrace remnant where there is none we conclude that important factors other than morphometric ones are important in determining loess distribution in loess landscapes in active tectonic regions these may include internal changes to regolith affecting erodibility or vegetation or topographic interaction with wind patterns affecting loess trapping

the influence of the evolution of the pyrenees on adjacent basins abstract important thicknesses of syn and post orogenic sediments are observed in the southern part of the aquitaine basin and in the north of the ebro basin their deposition cannot be explained only as a result of the extensional history of the early cretaceous thus the influence of the compression associated with the pyrenees formation upon the subsidence of these basins is studied europe and iberia are considered to behave as two semi infinite elastic plates the evolution through time of the sedimentary thicknesses is explained by the deflections of these two plates induced not only by the topographic load of the pyrenees but also by additional forces 10 12 n m that may have their origin in the formation of a cold lithospheric root during the shortening a series of calculations is presented for an approximately north south profile across the aquitaine basin the pyrenees and the ebro basin a good fit for the shape of the basins and the gravity anomalies was obtained with flexural rigidities of 1 5 10 23 nm for the northern plate and the outer part of the southern plate and 1 4 10 21 nm for the inner part of the southern plate

fusion of airborne polarimetric and interferometric sar for classification of coastal environments airsar and topsar data were acquired over the wetlands of bolivar peninsula along the gulf coast of texas for mapping land cover types and topographic features such as beach ridges dunes and relict storm features classification of land cover over this wetlands and uplands environment is difficult because of the similarity of spectral signatures of the vegetation types in addition because the distribution of vegetation communities in coastal marshes is strongly related to salinity which in turn is largely dictated by frequency and duration of inundation surface topography is critical to determination of the vegetation characteristics at any location the potential advantages of multisensor classification including in particular topographic information from a topsar dem are investigated an approach which employs a class dependent feature selection procedure in conjunction with pairwise bayesian classifiers is proposed and applied to the polarimetric and interferometric sar data

analysis and evaluation of the nasa jpl topsar across track interferometric sar system we have evaluated the accuracy of digital elevation models dem s generated by the jpwnasa topsar synthetic aperture radar interferometer instrument by acquiring topographic radar data in the summer of 1992 over the national training center near ft irwin california and comparing the measurements to a very accurate digital elevation model derived for this area by the us army topographic engineering center tec fiducial corner reflectors were deployed in the area and their locations were determined to cm accuracy by the defense mapping agency dma dem s generated from the acquired radar data were rotated and translated to precisely overlay the reference dem allowing an analysis of the achieved height accuracy we present here a detailed description of horizontal and vertical errors and their characteristics the standard deviation measured over a 5 6 x 7 km area was approximately 2 m the corresponding figures for relatively flat areas were in the 1 2 meter range and for mountainous areas in the 2 3 meter range consistent with theoretical expectations we also discuss key factors that presently limit the system performance