modeling flood dynamics along the superelevated channel belt of the yellow river over the last 3000 years the yellow river china experienced 1000 levee breaches during the last 3000 years a reduced complexity model is developed in this study to explore the effects of climate change and human activity on flood levels levee breaches and river avulsions the model integrates yearly morphological change along a channel belt with daily river fluxes and hourly evolution of levee breaches model sensitivity analysis reveals that under natural conditions superelevation of the channel belt dominates flood frequency when there is significant human accelerated basin erosion and breach repair the dominant factors shift to a combination of mean annual precipitation superelevation critical shear stress of weak channel banks and the time interval between breach initiation and its repair the effect of precipitation on flood frequency is amplified by land use changes in the hinterland particularly in the erodible loess plateau uncertainty analysis estimates the most likely values of the dominant factors for six historical periods between 850 b c and a d 1839 which are used to quantitatively reconstruct flood dynamics during 850 b c to a d 1839 when the sediment load increased fourfold the breach recurrence interval was shortened from more than 500 years to less than 6 years and the breach outflow rate increased 27 times river management practices during a d 1579 to a d 1839 focused on levees and triggered a severe positive feedback of increased levee heights and flood hazard exacerbation raising the levee heights proved to be ineffective for sustainable flood management

broad synchrony of a late glacial glacier advance and the highstand of palaeolake tauca in the bolivian altiplano the morphology and sedimentology of glacially influenced fan deltas on massifs at the margin of the southern altiplano bolivia suggest a broadly synchronous expansion of glaciers and palaeolake tauca during the late glacial interval this is shown by sedimentary successions of glacigenic glacifluvial and glacideltaic facies linking palaeoglaciers with palaeolake tauca on the flanks of cerro azanaques and cerro tunupa at altitudes of 3770 3720 m radiocarbon dates from peat overlain by glacial diamict and glacifluvial outwash indicate that glaciers in this area reached their last glacial maximum extent after ca 13 300 14 c yr bp glacifluvial fan deltas contiguous with the moraines confirm that the advance coincided with a highstand of palaeolake tauca radiocarbon dated to the interval ca 13 500 11 500 yr bp modeling of climatic controls on this glacier advance suggests the primary forcing was increased summer wet season moisture possibly amounting to 600 mm above the modern values of 200 400 mm greater cloud cover probably depressed local temperatures and reduced the evaporation rate the consequent rise in effective annual moisture p e comfortably accommodates a palaeolake 48 50 10 3 km 2 in area and up to 100 m deep in the southern altiplano because the palaeoglacier equilibrium line altitudes rose toward the south and west like the gradient of modern precipitation totals we conclude that the increased late glacial moisture was brought by weather systems similar to those of the present but that atmospheric conditions were cloudier and cooler 1997 john wiley sons ltd

modern and last local glacial maximum snowlines in the central andes of peru bolivia and northern chile late pleistocene snowlines in the central andes were 500 1200 m lower than at present radiocarbon dates imply that the late pleistocene glacial maximum in the region occurred prior to 20 14c ka but lack of maximum limiting ages adds considerable uncertainty to the exact timing snowline modeling demonstrates that snowlines in the eastern and western cordilleras of the central andes respond differently to temperature and precipitation changes in the eastern cordillera the snowline is near the level of the annual 0 c isotherm and melting occurs throughout the year here snowlines are sensitive to temperature changes but relatively insensitive to accumulation changes in the western cordillera the snowline rises 1000 higher owing to increasing aridity and the snowline exhibits a much stronger sensitivity to accumulation changes the consistent 1200 m snowline depression along the eastern cordilleras of the central andes can be modeled by a mean annual cooling of 5 9 c this is inconsistent with the 2 c cooling in tropical sea surface temperatures suggested by climap reconstructions the 800 1000 m snowline depression in the western cordillera cannot be accounted for solely by cooling but also requires an increase in precipitation

hydraulic performance of an embankment weir with rough crest abstractan experimental study was conducted on a large embankment weir with smooth and rough crests for a range of flow conditions 0 011 q 0 226 m3 s close agreement between the rough and smooth crest experiments was observed in terms of flow patterns free surface profiles and pressure distributions the crest roughness had effects on the velocity distributions the boundary layer properties and the shear stress on the rough crest the velocity distributions were shifted upwards increasing the growth rate of the boundary layer the calculation of the shear stresses with the law of the wall outer flow region and momentum integral methods showed consistent results of about g h 0 0015 0 0018 for the smooth crest and of g h 0 0024 for the rough crest the crest roughness reduced the discharge performance while upstream and downstream ramps did not have any effects the present observations highlighted the relevance of roughness and scaling on the hydraulic performances of weirs

permo triassic tectonism in volcanic arc sequences of the western u s cordillera and implications for the sonoma orogeny the permo triassic sonoma orogeny western u s cordillera involved tight folding and imbricate thrust faulting of basinal strata of the golconda allochthon this event is generally interpreted in terms of accretion of upper paleozoic volcanic arc rocks of the western u s cordillera mccloud arc to the north american continent either via back arc basin closure or arc continent collision the structural history of the mccloud arc during the sonoma orogeny is poorly understood however as are the implications of this history for tectonic models this paper presents a synthesis of the permian to triassic stratigraphic and structural evolution of the mccloud arc incorporating new data from the pine forest range northwest nevada the synthesis indicates that on a regional scale the arc was affected by widespread uplift but only local tilting folding and faulting in the late permian to early triassic the timing of permo triassic tectonic activity in the mccloud arc is thus similar to the middle permian to early triassic age of deformation in the golconda allochthon but the structures produced in the two groups of rocks differ markedly the significance of this contrasting structural response to sonoma age tectonism can be evaluated by comparison with other better understood examples of arc continent accretion back arc basin closure in the southern andes compressional arc continent collision in new guinea and extensional arc continent collision in the mediterranean this comparison indicates that the contrasting structural history of the mccloud arc and golconda allochthon is entirely compatible with an arc continent accretion model for the sonoma orogeny and cannot be used as a basis for concluding that the mccloud arc was not involved in the orogenic event the comparison further indicates that either back arc basin closure or compressional arc continent collision are the most likely settings for the sonoma orogeny in contrast an extensional mediterranean style arc continent collision as has been recently proposed for the earlier middle paleozoic antler orogeny is probably not an appropriate analogue for the sonoma orogeny the weak structural response of the mccloud arc during sonoman compression also provides new constraints on the specific processes involved in arc accretion either via arc continent collision or back arc basin closure these constraints suggest that there may be few fundamental differences between the two models during the final stages of arc accretion regardless of tectonic setting permo triassic uplift and associated deformation in the mccloud arc should be considered as much a response to the sonoma orogeny as is tight folding and imbricate faulting in the golconda allochthon

late quaternary glacial history in the encierro valley northern chile 29 s deduced from 10be surface exposure dating abstract the late pleistocene glacial and climate history in the dry central andes is not well known so far mainly because of the lack of suitable material for radiocarbon dating in order to establish a glacial chronology we applied surface exposure dating using in situ produced cosmogenic 10be for 11 boulders from moraines in the encierro valley 29 s northern chile we discuss sample specific effects topographic shielding sample geometry rock surface erosion inheritance and post depositional geomorphological instability and systematic uncertainties production rate of 10be latitude and altitude scaling minor glacial advances probably occurred around 11 6 1 2 ka bp whereas major advances are recorded at 14 0 1 4 ka bp and eventually at 24 1 2 4 ka bp this may indicate synchrony of some late pleistocene glacial advances south and north of the so called arid diagonal 25 s increased precipitation plays a dominant role for the observed late pleistocene glacial advances in the absence of further glacial chronologies south and north of the research area it remains difficult to disentangle the influence of the complex and in space and time variable westerlies and the tropical summer precipitation regime

experimental and numerical analysis of side weir flows in a converging channel abstractthis paper investigates the lateral outflow over a short crested side weir inserted in a converging rectangular channel with linearly decreasing width in the flow direction this type of ov

paleoclimate reconstruction along the pole equator pole transect of the americas pep 1 examples are presented of inter hemispheric comparison of instrumental climate and paleoclimate proxy records from the americas for di erent temporal scales despite a certain symmetry of seasonal precipitation patterns along the pep 1 transect decadal variability of winter precipitation shows di erent characteristics in terms of amplitude and frequency in both the last 100 and last 1000 years such di erences in variability are also seen in a comparison of time series of di erent el nin8 o southern oscillation proxy records from north and south america however these di erences do not appear to a ect the spatial correlation with paci c sea surface temperature patterns local and regional di erences in response to climate change are even more pronounced for records with lower temporal resolution and inter hemispheric synchroneity may or may not be indicative of the same forcing this aspect is illustrated in an inter hemispheric comparison of the last 1000 years of glacier variability and of the full and lateglacial lake level history 1999 elsevier science ltd all rights reserved

side weir in u shaped channels numerical investigations of flow over side weirs in u shaped channel are reported numerical models are obtained from energy principles and solved by a finite difference method the results are presented in graphical form the study covers sub and supercritical flow regimes derived expressions for the side weir discharge and water surface profiles in u shaped channels for these regimes are compared with experimental results necessary charts are presented for practical engineering use

lateral outflow over side weirs note 66 reference lch article 1987 011 record created on 2007 04 24 modified on 2016 08 08

evidence of an lgm cooling in nw argentina 22 s derived from a glacier climate model abstract a climate glacier model is used to interpret late pleistocene maximum glaciations in the nw argentinan andes 22 s according to the model massive cooling combined with a moderate precipitation increase is necessary to explain maximum glacier extension even given a factor of 2 4 precipitation increase the model indicates that temperatures must have been lowered by 4 5 8 c suggesting that maximum glaciation probably occurred during full glacial times of mis 2 25 18 ka this conclusion is supported by dated proglacial lake sediments and evidence of past glacial geometry the extremely long tongues and low accumulation area ratios indicate that ablation was reduced during cold periods in agreement with the model a strong relationship exists between glacier geometry and prevailing climate contrary to the precipitation controlled late glacial 12 10 ka maximum glaciation of the arid central andes in southern peru and northern chile the glaciations on the much more humid eastern andean slope are mainly controlled by temperature and therefore reached their maximum extent during the mis 2 cold conditions

overtopping induced failure of noncohesive homogeneous fluvial dikes accurate predictions of breach characteristics are necessary to reliably estimate the outflow hydrograph and the resulting inundation close to fluvial dikes laboratory experiments on the breaching of fluvial sand dikes were performed considering a flow parallel to the dike axis the breach was triggered by overtopping the dike crest a detailed monitoring of the transient evolution of the breach geometry was conducted providing key insights into the gradual and complex processes involved in fluvial dike failure the breach develops in two phases 1 the breach becomes gradually wider and deeper eroding on the downstream side along the main channel and 2 breach widening controlled by side slope failures continuing in the downstream direction only increasing the inflow discharge in the main channel the breach formation time decreases significantly and the erosion occurs preferentially on the downstream side the downstream boundary condition has a strong influence on the breach geometry and the resulting outflow hydrograph

late pleistocene climate conditions in the north chilean andes drawn from a climate glacier model a climate glacier model was used to reconstruct late glacial climate conditions from two case study glaciers at 18 and 22 s in the arid sub tropical western andes of northern chile the model uses i the geometry of the late glacial maximum glaciation ii modern diurnal and annual cycles amplitudes and lapse rates of the climate iii empirical statistical sublimation melt and accumulation models developed for this area and iv dynamic ice flow through two known cross sections for steady state conditions the model is validated with modern conditions and compares favorably with the glaciological features of today the mass balance model calculates the modern equilibrium line altitude at 18 s as high as 5850 m field data 5800 m whereas no glaciers exist in the fully arid southern area at 22 s despite altitudes above 6000 m and continuous permafrost for late glacial times the model results suggest a substantial increase in tropical summer precipitation ap 840 50 10 mm a 1 for the northern test area 1000 10 30 mm a 1 for the southern test area and a moderate temperature depression t 4 4 0 1 0 2 c at 18 s 3 2 0 1 c at 22 s extratropical frontal winter precipitation june september was 15 of the total annual precipitation a scenario with higher winter precipitation from the westerlies circulation belt does not yield a numerical solution which matches the observed geometry of the glaciers therefore we conclude that an equatorward displacement of the westerlies must be discarded as a possible explanation for the late pleistocene glaciation in the andes of northern chile

first cosmogenic ages for glacial deposits from the plata range 33 s new inferences for quaternary landscape evolution in the central andes this paper presents the first numerical cosmogenic ages of glacial deposits from the eastern slope of the plata peak 6000 in the arid central andes 32 s the moraines are distributed along three different valleys vallecitos angostura and las mulas in the first only one moraine was identified and no blocks could be sampled for dating the other two have evidence of two glacial advances angostura i and angostura ii the advances loma de los morteritos i and ii were recognised in the las mulas valley in both cases first and second advances are preserved at a similar altitude surface boulders on the top of moraines were sampled for be10 obtained ages are all similar and late pleistocene in age they fit very well with local stratigraphy and regional paleoclimate evidence the loma de los morteritos moraine ii located at 3000 masl dated to 25 000 years ages of 8 000 and 12 000 years were found for the angostura ii deposit 3300 masl an age was obtained for the outwash deposit identified along the el salto valley 69 000 years associated with a late pleistocene drift quantitative datings presented here improve knowledge about the glacial chronology of the plata range and quaternary stratigraphy of the central andes even though they represent a maximum age for these glacial advances new findings support the occurrence of two late pleistocene glacial advances and an older one in the blanco river valley adjusted ages around 8 000 and 25 000 years for younger stage could be evidence of the last glacial maximum lgm period for this region

discharge coefficient for sharp crested side weir in subcritical flow to estimate the outflow over a rectangular sharp crested side weir the discharge coefficient in the weir equation needs to be known although this type of structure has been designed and used extensively by hydraulic engineers a universally acceptable discharge coefficient does not exist in this study over 250 laboratory tests were conducted and the results were analyzed to find the influence of the flow hydraulics and the geometric channel and weir shapes on the coefficient the results show that for subcritical flow the de marchi assumption of constant energy is acceptable and the weir discharge can therefore be used furthermore it was discovered that the de marchi coefficient of discharge is a function of the upstream froude number and the ratios of weir height to upstream depth and weir length to channel width whereas the channel slope in subcritical flow can be ignored hence an accurate equation for the coefficient of discharge is introduced

hydraulics of embankment weirs embankment weirs often found in engineering applications with a side slope 1v 2h are considered in this paper for free overflow the discharge coefficient is determined in terms of relative crest length for long broad crested broad crested short crested and thin crested weirs a considerable increase of capacity is noted when compared to broad crested weirs with vertical face for submerged overflow four regimes are identified 1 a jump 2 plunging jet 3 surface wave and 4 surface jet particular attention is focused on plunging jets and surface waves the flow regimes are discussed in terms of submergence crest length and modular limit a description is given of the forward and backward recirculation zones with indications of typical lengths also the entire velocity field is described including the maximum forward and backward velocities and the velocity distribution in arbitrary sections of the tailwater region it is found that plunging jets and surface jets are hydraulically similar and that the profile of one regime can be transformed into the other profile by inversion about the median all results are generalized and can be directly applied

numerical and experimental modeling of levee breach including slumping failure of breach sides abstractthe overtopping failure of noncohesive earthen levees was investigated by considering sediment transport by flowing water and including slumping failure due to slope instability the breach

rectangular lateral weirs in circular open channels a theoretical expression for the outflow through a rectangular lateral weir located in a circular open channel is derived using the results of an existing theory of lateral efflux through a two dimensional conduit outlet the development of the present model is similar to a procedure that earlier yielded the theoretical expression for the outflow through a rectangular lateral weir located in a rectangular open channel on the basis of the free streamline theory in the present case the theoretical weir discharge coefficient is expressed as a function of parameters relating the geometry of the rectangular lateral weir and the circular open channel and a velocity parameter which is a function of the dimensionless flow depth the dimensionless weir sill height and the froude number of the approach flow experimental results are presented to verify the proposed model

glacier climate interaction at low latitudes in the low latitudes there is an absence of major thermal seasonality yet there are three different climate regimes related to global circulation patterns and their seasonal oscillation the humid inner tropics the dry subtropics and intermediate between these two the outer tropics for the respective glacier regimes the vertical profiles of specific mass balance vbps are modeled considering vertical gradients of accumulation air temperature and albedo the duration of the ablation period and a factor for the ratio between melting and sublimation the model is first calibrated with data from hintereisferner austrian alps and is then applied to tropical conditions the simulated vbp matches well the measured profiles from irian jaya and mount kenya due to lack of field evidence the subtropical vbp cannot be verified directly however application of the respective model versions separately to the humid and dry seasons of the outer tropical glaciar uruashraju cordillera blanca peru provides reasonable results glaciers in the humid inner tropics are considered to be most sensitive to variations in air temperature while dry subtropical glaciers are most sensitive to changes in air humidity the two seasons of the outer tropics have to be viewed from these different perspectives

design and calibration of a compound sharp crested weir this paper describes the design and calibration of a compound sharp crested weir consisting of two triangular parts with different notch angles this weir provides accurate measurement for a wide range of flows without discontinuities the lower triangular part of the weir handles the normal range of discharges at the measurement structure while the upper part measures the occasional higher peak flows this weir will be installed on the crest of small concrete gravity dams for measuring runoff in experimental catchments the weir was calibrated in the laboratory using a scaled model different geometries combination of notch angles were tested in order to validate the proposed theoretical discharge equations

absence of last glacial maximum records in lowland tropical forests abstract environmental conditions of the lowland tropical forests during the last glacial maximum lgm between ca 20 000 and 18 00014c yr b p are reevaluated in terms of dating control and lithology analyzed in seven pollen records from south america the reevaluation shows that probably in none of the published records are lgm sediments present or abundant this conclusion is based on the occurrence of abrupt lithologic changes coupled with changes in sedimentation rate interpolated from radiocarbon dates these findings suggest that the lgm was represented probably by a hiatus of several thousand years indicative of drier climates than before or after

antarctic like temperature variations in the tropical andes recorded by glaciers and lakes during the last deglaciation abstract the respective impacts of northern and southern hemispheric climatic changes on the tropics during the last deglaciation remain poorly understood in the high tropical andes the antarctic cold reversal acr 14 3 12 9 ka bp is better represented among morainic records than the younger dryas 12 9 11 7 ka bp however in the altiplano basin bolivia two cold periods of the northern hemisphere heinrich stadial 1a 16 5 14 5 ka bp and the younger dryas are synchronous with i major advances or standstills of paleoglaciers and ii the highstands of giant paleolakes tauca and coipasa here we present new cosmic ray exposure cre ages from glacial landforms of the bolivian andes that formed during the last deglaciation termination 1 we reconstruct the equilibrium line altitudes ela associated with each moraine and use them in an inverse algorithm combining paleoglaciers and paleolake budgets to derive temperature and precipitation during the last deglaciation our temperature reconstruction t relative to present day yields a consistent regional trend of progressive warming from t 5 to 2 5 c during 17 14 5 ka bp followed by a return to colder conditions around 4 c during the acr 14 5 12 9 ka bp the coipasa highstand 12 9 11 8 ka bp is coeval with another warming trend followed by t stabilization at the onset of the holocene ca 10 ka bp around 3 c our results suggest that during the last deglaciation 20 10 ka bp atmospheric temperatures in the tropical andes mimicked antarctic variability whereas precipitation over the altiplano was driven by changes in the northern hemisphere

the timing and magnitude of mountain glaciation in the tropical andes the andes of ecuador peru and bolivia host the majority of the world s tropical glaciers in the tropical andes glaciers accumulate during the wet season austral summer and ablate year round precipitation is delivered mainly by easterlies and decreases both n s and e w chronological control for the timing of glacial advances in the tropical andes varies in ecuador six to seven advances have been identified dating is based on radiocarbon ages timing of the local last glacial maximum lgm and the existence of younger dryas advances remain controversial in peru local variability in glaciation patterns is apparent surface exposure dating in the cordillera blanca and junin plain suggests that the local lgm may have been early 30 ka although uncertainties in age calculations remain the local lgm was followed by a lateglacial readvance stillstand and preceded by larger glaciations in contrast preliminary data from an intervening massif indicate that the largest moraines are lateglacial chronologies from bolivia also suggest local variability in leeward milluni and san francisco valleys local lgm moraines descend to 4300 m above sea level a s l whereas in windward zongo valley lateglacial moraines reach 3400 m a s l atlantic and pacific sea surface temperatures el nino southern oscillation and insolation changes all likely play roles in mediating tropical andean glacial cycles copyright 2008 john wiley sons ltd additional supporting information may be found in the online version of this article

late pleistocene climate and water budget of the south american altiplano abstract geomorphic evidence from the peruvian bolivian altiplano indicates that during episodes prior to 28 000 and around 12 500 11 000 yr b p lakes covered an area about six and four times as large as at present respectively within the constraints of the heat and water budget model calculations are used to estimate the precipitation rate that would allow hydrologic equilibrium on this basis it is suggested that rainfall on the altiplano during the episodes of enlarged lakes was respectively some 300 and 200 mm annum 1 larger than at present representing increases of about 75 and 50 respectively field evidence suggests that the episodes of enlarged lakes on the altiplano may have preceded or coincided with periods of maximum glaciation in the neigh boring andes in this region with high elevation of the ice equilibrium line increased precipitation is particularly conducive to glaciation

u pb sm nd and rb sr geochronological and isotopic study of northern sierra nevada ophiolitic assemblages california distinct ophiolitic assemblages occur as oceanic basement within three of the four regional tectonic belts of the northern sierra nevada new u pb zircon sm nd and rb sr data are presented for each assemblage providing critical geochronological and isotopic constraints on the petrogenesis and tectonic evolution of the ophiolitic and associated ensimatic assemblages ophiolitic assemblages include from west to east the smartville complex central belt and feather river belt the smartville complex represents an island arc volcanic plutonic sequence with a major late stage sheeted dike swarm the sm nd systems from a wide compositional spectrum of rocks record a 178 21 ma petrogenetic age and an nd t 9 2 0 6 zircon u pb systems on an uppermost dacite yield a 164 2 ma age and on a number of plagiogranite screens and dikes from the sheeted complex 162 1 ma ages the central and feather river belts are structurally complex polygenetic assemblages the u pb zircon and sm nd systems record major 205 ma and 315 ma petrogenetic events respectively both involving depleted mantle derived magmas such magmatism probably occurred in marginal basin transform systems developed within an older oceanic depleted mantle basement regime both sm nd and u pb zircon systems show local components of proterozoic sialic material the sialic contaminants were probably introduced into the system as craton derived detritus it is doubtful that any of the ophiolitic assemblages studied represent genetically related crust upper mantle sequences generated during the development of new oceanic lithosphere integration of the geochronological data with geological relations reveals a pattern of petrogenesis and tectonics whereby progressively younger ensimatic terranes were added to the continental margin through time by plate convergence and were ultimately welded into north american sial by a crosscutting batholithic belt this accretionary pattern is reflected in both the protolith ages and deformation metamorphic ages of each of the regional belts which progressively young westward crustal components of the accreted ensimatic terranes grew by mainly basaltic igneous activity within island arc marginal basin and leaky transform systems adjacent to the continent edge prior to final tectonic accretion such complexities are suggested to be typical of cordilleran type ophiolites and representative of the circum pacific erogenic style

influence of lateral water withdrawal on bed form geometry in a channel in flood protection engineering side weirs or overflow dams are used to divert water in a controlled way into flood plains as soon as the discharge capacity of the main channel is reached because of the lateral loss of water the sediment transport capacity is reduced resulting in local sediment deposition near the side overflow moreover bed form characteristics such as length height steepness and stoss and lee slope angle are affected by the lateral water withdrawal both phenomena are responsible for an increased side overflow intensity compared with plane bed conditions the results from a systematic flume study show that the shape of observed bed forms is highly threedimensional and that three distinct regions along the channel axis can be identified the first one extends from the channel entrance to the upstream weir corner the second one comprises the reach of the weir and the third one represents the reach downstream of the weir the description of bed form shape by approaches from literature shows reasonable agreement with measured bed form geometry

lake level chronology on the southern bolivian altiplano 18 23 s during late glacial time and the early holocene stratigraphic analyses of outcrops shorelines and diatoms from the southern bolivian altiplano uyuni coipasa basin reveal two major lacustrine phases during the late glacial period and the early holocene based on a chronology established by radiocarbon and u th control a comparison of14c and230th 234u ages shows that during times of high lake level radiocarbon ages are valid however during low water periods 14c ages must be corrected for a reservoir effect the lacustrine tauca phase started a little before 16 00014c yr b p and the lake level reached its maximum between 13 000 and 12 00014c yr b p a dry event ticana occurred after ca 12 000 and before 950014c yr b p a moderate lacustrine oscillation coipasa event occurred between ca 9500 and 850014c yr b p using a reservoir corrected conventional14c chronology comparisons between the lake level chronology in the uyuni coipasa basin and data from other southern tropical areas of south america suggest that the lacustrine evolution may reflect large scale climatic changes

diversion of flow and sediment towards a side channel separated from a river by a longitudinal training dam a human made entrance to a side channel separated from the river by a longitudinal training dam can be considered a new emergent type of river bifurcation to understand the processes controlling the diversion of flow and sediment towards the side channel at such bifurcations a comprehensive field monitoring programme was performed in the waal river which is the main branch of the rhine river in the netherlands local processes govern the flow field in the bifurcation region the angle between the main river flow and the flow into the side channel increases with decreasing lateral and longitudinal distance to the bifurcation point which corresponds to the head of the training dam the general flow pattern can be well reproduced with a uniform depth potential flow model consisting of a superposition of main channel flow and lateral outflow for submerged flow conditions over the sill the side channel hydraulic conditions influence the exchange processes yet free flow side weir theory describes the flow field at this bifurcation type qualitatively well the vertical flow structure in the side channel which governs the sediment exchange between the main channel and the side channel is steered by the geometrical details of the sill the presence of the sill structure is key to controlling the morphological stability of this type of bifurcation given its primary influence on bed load sediment import and exerts an indirect impact on suspended sediment exchange

late quaternary precessional cycles of terrigenous sediment input off the norte chico chile 27 5 s and palaeoclimatic implications abstract the palaeoclimatic conditions during the last glacial maximum lgm of southern south america and especially latitudinal shifts of the southern westerly wind belt are still discussed controversially longer palaeoclimatic records covering the late quaternary are rare a particularly sensitive area to late quaternary climatic changes is the norte chico northern chile because of its extreme climatic gradients small shifts of the present climatic zonation could cause significant variations of the terrestrial sedimentary environment which would be recorded in marine terrigenous sediments to unveil the history of shifting climatic zones in northern chile we present a sedimentological study of a marine sediment core geob 3375 1 from the continental slope off the norte chico 27 5 s sedimentological investigations include bulk and silt grain size determinations by sieving atterberg separation and detailed sedigraph analyses additionally clay mineralogical parameters were obtained by x ray diffraction methods the 14c dated core covering the time span from approximately 10 000 to 120 000 cal yr b p consists of hemipelagic sediments terrigenous sedimentological parameters reveal a strong cyclicity which is interpreted in terms of variations of sediment provenance modifications of the terrestrial weathering regimes and modes of sediment input to the ocean these interpretations imply cyclic variations between comparatively arid climates and more humid conditions with seasonal precipitation for northern chile 27 5 s through the late quaternary the cyclicity of the terrigenous sediment parameters is strongly dominated by precessional cycles for the palaeoclimatic signal this means that more humid conditions coincide with maxima of the precession index as e g during the lgm higher seasonal precipitation for this part of chile is most likely derived from frontal winter rain of the southern westerlies thus the data presented here favour not only an equatorward shift of this atmospheric circulation system during the lgm but also precession controlled latitudinal movements throughout the late quaternary precessional forcing of latitudinal movements of the westerly atmospheric circulation system may be conceivable through teleconnections to the northern hemisphere monsoonal system in the atlantic ocean region

subcritical side weir flow at high lateral discharge side weirs count among the important hydraulic structures for flow derivation in flood schemes or sewer networks in this paper the prismatic side weir in the rectangular channel is considered for entirely subcritical flow based on the momentum and energy equations relationships are developed for the lateral outflow intensity the local lateral outflow angle the energy and momentum correction coefficients and the relationship between the local streamwise component of the lateral outflow velocity and the average channel flow velocity the governing equations are then numerically solved and the results compared with hydraulic laboratory observations indicating that the momentum approach may be considered superior to the energy approach the role of the momentum and energy correction coefficients is thereby particularly analyzed stating that their correct inclusion both as absolute values and their local variation along a side weir have to be accounted for if the local discharge relative to the approach flow discharge tends to zero

silurian plutonism in the trinity terrane neoproterozoic and ordovician klamath mountains california united states new data indicate that the trinity terrane of northern california is a polygenetic composite terrane rather than a single slice of oceanic lithosphere we suggest approximately one third of the trinity terrane consists of silurian intrusive rocks that represent the roots of a previously unrecognized silurian magmatic arc crosscutting relations and u pb zircon isotopic data document at least one early paleozoic deformation in the trinity terrane of northern california a ductile shear zone between neoproterozoic metagabbro and ordovician harzburgite is intruded by the upper silurian china mountain pluton this evidence indicates a major early paleozoic shear zone formed in the eastern klamath mountains after the middle ordovician but prior to late silurian plutonism

discharge coefficient for compound sharp crested side weirs in subcritical flow conditions side weirs are one of the most common diversion structures used for flow control irrigation drainage networks and waste water channels side weirs are generally rectangular sharp crested in form and hence have some limitations in precise flow measurement for accurate flow measurement and management in wide range of discharges use of compound side weirs are suggested in this study experiments have been carried out in a rectangular compound side weir with variable heights and widths it was determined that discharge coefficient of a compound side weir is a function of upstream froude number fr1 ratio of weighted crest height of weir to upstream water depth w y1 and ratio of weir length to upstream water depth l y1 based on the experimental data and regression modeling a dimensionless equation has been developed for prediction of the discharge coefficient and an equation has been proposed for estimation of flow discharge in compound rectangular sharp crested side weirs through comparison of results of these equations and experimental data good agreement was achieved the mean and maximum relative errors of the discharge equation were 2 3 and 10 7 respectively

side weir flow on a movable bed abstractside weirs are hydraulic structures widely used for flow control in rivers and canals whenever the water level rises above the side weir crest elevation a fraction of the main flow is diverted so that the water discharge flowing downstream in the main channel is reduced in movable bed channels the lateral outflow may have significant interactions with the sediment transport processes affecting the side weir flow the spilled discharge creates a reduction of the downstream sediment transport capacity with a consequent deposition in the side weir proximity in addition sediment in the main channel can be diverted into the lateral branch to investigate these interactions experimental data at the laboratory scale have been collected and analyzed the increase of the spilled discharge induced by the local sediment deposition is described according to the classical de marchi hypothesis furthermore the sediment transport leaving the main channel through the lateral structure is modeled in terms

local scouring due to turbulent water jets downstream of a trapezoidal drop laboratory experiments and stability analysis 1 three series of laboratory experiments were run varying the flume water discharge and the downstream water depth to investigate local scouring downstream of a trapezoidal drop followed by a rigid apron three different kinds of jets developing downstream of the drop were observed a submerged jet a surface wave jet and an oscillating jet the oscillating jet is defined as a jet which changes intermittently between a surface wave jet and a submerged jet a different development of the scouring process due to the different kinds of jet was observed a submerged jet produced a local scouring with a downstream dune while a surface wave jet produced a local scouring with both an upstream and a downstream dune the scouring process due to the oscillating jet was the result of the interaction of the scouring processes due to a submerged jet and a surface wave jet a stability analysis of the surface wave jet was performed with both a flat and a scoured bed by means of the modified de saint venant equations that is with correction terms accounting for the curvature of the streamlines the stability of the surface wave jet is affected by the presence of the scoured bed which weakens its stability properties

a 25 000 year tropical climate history from bolivian ice cores ice cores that were recovered from the summit of sajama mountain in bolivia provide carbon 14 dated tropical records and extend to the late glacial stage lgs oxygen isotopic ratios of the ice decreased 5 4 per mil between the early holocene and the last glacial maximum which is consistent with values from other ice cores the abrupt onset and termination of a younger dryas type event suggest atmospheric processes as the probable drivers regional accumulation increased during the lgs during deglaciation and over the past 3000 years which is concurrent with higher water levels in regional paleolakes unlike polar cores sajama glacial ice contains eight times less dust than the holocene ice which reflects wetter conditions and extensive snow cover

glacier and climate reconstruction at tres lagunas nw argentina based on 10be surface exposure dating and lake sediment analyses abstract we present 35 10 be surface exposure ages from quartzite moraine boulders at tres lagunas in the sierra de santa victoria nw argentina additionally an 8 m sediment core from a glacial lake was investigated to provide independent radiocarbon age control the oldest and most extensive glaciation occurred 116 3 ka and likely coincides with the lake transgression phase ouki on the altiplano maximum glaciation in phase with the global last glacial maximum lgm is dated to 22 25 ka and documents a glacial mass balance response to substantially lower temperatures and minor precipitation increase in phase with the sajsi lake transgression phase after initial deglaciation and formation of a small paleolake at tres lagunas a glacial readvance is documented by an outwash diamict in the sediment core and radiocarbon dated to 19 17 ka as well as by a moraine surface exposure dated to 17 ka the most prominent moraine was deposited at 14 5 ka coinciding with the lake transgression phase tauca on the altiplano this late glacial advance reflects the massive intensification of the south american summer monsoon sasm in response to northern hemispheric cooling during heinrich i and the resultant southward shift of the intertropical convergence zone itcz and la nina like conditions in the eastern equatorial pacific rapid deglaciation started after 14 5 ka interrupted only by minor glacial still stands at 13 8 1 5 ka and 12 0 1 5 ka the latter one correlating with the coipasa transgression phase on the altiplano and the younger dryas

2004 indian ocean tsunami flow velocity measurements from survivor videos 1 the tsunami of 26th december 2004 severely affected banda aceh along the north tip of sumatra indonesia at a distance of 250 km from the epicenter of the magnitude 9 0 earthquake this tsunami flow velocity analysis focused on two survivor videos recorded within banda aceh more than 3 km from the open ocean the exact locations of the tsunami eyewitness video recordings were revisited by the survey team between february 22 and 25 2005 to record camera calibration ground control points the motion of the camera during the recordings was determined the individual video images were rectified with a direct linear transformation dlt assuming a planar water surface at the level finally a cross correlation based particle image velocimetry piv analysis was applied to the rectified video images to determine instantaneous tsunami flow velocity fields the measured tsunami flow velocities were within the range of 2 to 5 m s

timing of the late quaternary glaciation in the andes from 15 to 40 s the central andes play a pivotal role for glacier and climate reconstruction along the american pole equator pole transect nevertheless knowledge about late quaternary palaeoenvir onmental changes in this region is extremely limited with the advent and application of surface exposure dating during the last few years the establishment of more detailed glacial chronologies could provide important insights into forcings and mechanisms of glaciation and climate change this paper reviews previously published exposure ages and compares them with independent age control on glacial chronologies and with information about the palaeohydrological conditions although available data are still very limited and there are remaining systematic uncertainties related to surface exposure dating the following simplified palaeoglacial palaeoclimate model is presented to serve as a testable hypothesis for future studies i glaciers in the humid tropical andes were mainly temperature sensitive and therefore advanced during temperature minima advances are dated to 20 25 ka 15 ka and 11 13 ka i e synchronous to the global last glacial maximum lgm the heinrich event 1 and the younger dryas antarctic cold reversal ii further south and west precipitation decreases and glaciers therefore become more precipitation sensitive maximum or at least prominent glacial advances as far south as 308 s are dated into the lateglacial i e synchronous with lake transgression phases tauca 14 18 ka and coipasa 11 13 ka iii between 30 and 408 s glaciers reached their maximum extent much earlier during the pre lgm 35 40 ka this is attributed to a northward shift and or intensification of the westerlies whereas conditions during the global lgm were too dry to allow for significant glacial advances iv south of 408 glaciers become temperature sensitive again and reached their maximum accordingly synchronous to the global lgm copyright 2008 john wiley sons ltd

tropical south america during the last glacial maximum evidence from glacial periglacial and fluvial records abstract the records of the lgm climates of tropical south america are still sparse compared to the vast region under consideration nevertheless a number of records hold up to critical evaluation early attempts to reconstruct the lgm temperature and precipitation conditions for the lgm around 21 14 c ka bp have suggested that relative to present lowland temperatures were on average only a few c cooler whereas in the andes the temperature depression was in the range of 6 8 c these reconstructions further suggested that tropical precipitation was more limited in both the lowlands and in the andes although recent pollen evidence supports significantly cooler tropical lowland temperatures during the lgm additional alkenone evidence from sea surface temperatures and model analysis are contradictory the data from tropical south america suggest that the late quaternary climatic changes of the lowlands as well as of the andean mountains reflect a response 1 to environmental changes in the source area of the moisture and 2 to global temperature fluctuations based on glacial periglacial and pollen evidence a lgm temperature depression of 5 6 c can be assumed for both tropical lowland south america and the andes these lgm values for the cooling correspond with recent coral records from barbados and the southwestern pacific ice core records from peru noble gas measurements in brazil and ocean core records from the western equatorial atlantic no difference in the value of lgm cooling can be recognised between the tropical lowlands and the high mountains of south america furthermore in all regions the lgm climates were more arid than the present day climates terrestrial records have not yet yielded records of younger dryas age apart from the tropical andes of ecuador where the younger dryas time is characterised by a cooler and drier climate pollen evidence for cooler younger dryas conditions comes from the bolivian andes

early warming of tropical south america at the last glacial interglacial transition glaciation in the humid tropical andes is a sensitive indicator of mean annual temperature here we present sedimentological data from lakes beyond the glacial limit in the tropical andes indicating that deglaciation from the last glacial maximum led substantial warming at high northern latitudes deglaciation from glacial maximum positions at lake titicaca peru bolivia 16 s and lake junin peru 11 s occurred 22 000 to 19 500 calendar years before the present several thousand years before the bolling allerod warming of the northern hemisphere and deglaciation of the sierra nevada united states 36 5 to 38 n the tropical andes deglaciated while climatic conditions remained regionally wet which reflects the dominant control of mean annual temperature on tropical glaciation

what controls the transition from confined to unconfined flow analysis of hydraulics in a river delta abstractrecent field work at the wax lake delta wld in coastal louisiana indicates lateral outflow from channels to islands upstream of the receiving basin in this region of the delta the flow t

discussion of laboratory study on 3d flow structures induced by zero height side weir and implications for 1d modeling by giovanni michelazzo hocine oumeraci and enio paris

late quaternary glacial and climate history of the pamir mountains derived from cosmogenic 10be exposure ages moraines southwest of lake yashilkul pamir tajikistan were dated using 10be exposure ages of boulder surfaces we found evidence for 1 an extensive glaciation 60 000 yr ago 2 a less extensive glacial advance which deposited a characteristic hummocky moraine lobe with exposure ages ranging from 11 000 to 47 000 yr probably deposited at or before 47 000 yr ago and 3 lateral moraines with exposure ages of 40 000 yr 27 000 yr and 19 000 yr respectively increasing aridity in the pamir is most likely responsible for the progressively limited extent of the glaciers during the late pleistocene

measuring the flow intrusion towards building areas during urban floods impact of the obstacles located in the streets and on the facade abstract this paper provides through laboratory experiments the flow discharge passing from a flooded street to a building area through different types of damaged openings a door a window and a gate along with a sensitivity analysis of this discharge to the presence of obstacles or facade details four flow regimes in the street are tested representing a high or low street slope with a high and low water depth these flows resemble that over rectangular side weirs with the major difference that obstacles are usually located near the opening in the street or on the facade 26 configurations of obstacles are then included one after the other and their impact on the flow intrusion is measured for the flow cases without obstacle the agreement of the semi analytical equations available in the literature strongly varies from one equation to another on the other hand the 220 tested flow cases reveal that the location of the obstacle with regards to the opening strongly modifies the impact of the obstacles that increasing the froude number tends to increase the impact of the obstacles and that obstacles have a higher impact on the intrusion discharge through a window than to a door or a gate finally we conclude that the largest obstacles typically parked cars located in the vicinity of openings should be somehow included in operational numerical models that calculate urban floods for a fair prediction of the intrusion discharge

speculative reconstruction of the mojave snow lake fault implications for paleozoic and mesozoic orogenesis in the western united states available evidence suggests that the mojave snow lake fault a major early cretaceous dextral fault with up to 400 km displacement formerly existed in what is now the axial part of the sierra nevada batholith regional relations suggest that the fault formerly continued in western nevada the mojave desert and in rocks now exposed in the salinian block restoration of 400 km of early cretaceous dextral displacement on the mojave snow lake fault leads to speculative but testable reconstructions of mesozoic and paleozoic tectonic features of california and nevada insights derived from these reconstructions include the following 1 two regionally extensive jurassic thrust belts of opposed vergence appear to have intersected in the northern sierra nevada the eastern east vergent thrust belt which includes the fencemaker and liming thrusts in western nevada and several east vergent thrusts in the northern sierra may be a contractional belt along which an early jurassic interarc or marginal basin was closed in middle to late jurassic time the western west vergent thrust belt is part of the classic nevadan orogen of the western klamath mountains and the western sierra metamorphic belt in which collisions and or thrusting of various island arc terranes occurred during middle and late jurassic time 2 the early mesozoic continental arc included paired belts of triassic jurassic blueschist and melange and igneous rocks including late triassic and younger plutons and volcanic rocks this conclusion is not new but the reconstruction provides a slightly different geometry than previously thought 3 sonomia the late paleozoic island arc terrane of the western u s may have formed a relatively narrow belt extending from northwestern nevada to the latitude of the western mojave desert the geologic development of the paleozoic basement complex of sonomia was very different from that of the cordilleran miogeocline in death valley and the mojave desert requiring that a continuation of the sonoma suture belt or golconda thrust must have extended southward through the sierra nevada batholith to the mojave region 4 a heterogeneous belt of permian to triassic or triassic deformation in the mojave and eastern sierra nevada together with the golconda allochthon in nevada may represent the protracted response to the collision of sonomia with the western margin of north america the contractional deformation continued during the evolution of the early mesozoic continental arc 5 several predictions can be made about the nature of concealed basement within the sierra nevada batholith and within western nevada the reconstruction suggests that elements of the antler and sonoma orogenic belts should underlie areas of the batholith and western nevada as a result of northward displacement along the mojave snow lake fault from the western mojave and southern sierra nevada

pollen studies in the junin area central peruvian andes laguna junin is a large lake 675 km long but only 4 m deep located in the grass covered altiplano at an altitude of 4 100 m northeast of lima pollen analysis of a 30 m core indicates that from about 12 000 yr ago until some time after 3 000 yr ago about 30 of the pollen was carried in by easterly winds from the east andean forests which today are at least 600 m lower in elevation contemporaneous pollen deposition in lakes on moraines of the last glaciation west of the junin plain was dominated by local grassland types and had little contribution from this easterly source at some time after 3 000 yr ago perhaps about 1 200 yr ago the pollen influx to laguna junin from this distant forest source greatly diminished perhaps because of deforestation by increased human populations between about 12 000 and 24 000 yr ago in the junin core the sparse pollen concentration was dominated by grassland types supplemented by polylepis acaena alnus and compositae blown in from the sub puna shrublands that may have occupied much of the east andean slopes in place of the humid forest that occurs there today the silty sediment in this section of the core is interpreted as outwash from piedmont glaciers that invaded the plain especially from the cordillera to the west these glaciers left a distinctive pattern of moraines and outwash fans which served to dam tine lake basin an unconformity in the sediment covers the time from about 24 000 to 39 000 yr ago when the lake was probably dry before this time the silty sediment and the dominance of grassland and shrubland pollen types indicates an earlier interval of glaciation recorded on the landscape by an older set of moraines and outwash fans which initially dammed the lake basin

late quaternary glaciation of the cordillera real bolivia glacial geological studies in tropical mountain areas of the southern hemisphere can be used to address two issues of late pleistocene climate change the global synchroneity of deglaciation and the magnitude of temperature reduction in the tropics radiocarbon dates from the cordillera real and from other areas in peru and bolivia suggest that late pleistocene glaciation culminated between 14 000 and 12 000 yr bp followed by rapid deglaciation because deglaciation was apparently synchronous with that in northern hemisphere regions insolation change at high latitudes may not have been the only factor that produced global deglaciation at this time late pleistocene glaciation in the cordillera real culminated when precipitation was 200 mm yr 1 higher and temperatures were 3 5 1 6 c lower than today this produced an equilibrium line altitude depression of about 300 100 m on the western side of the cordillera prior to this conditions were drier and probably at least as cold however the lack of moraines in the cordillera real dated to the last glacial maximum ca 18000 yr bp precludes using the equilibrium line altitude method to quantitatively evaluate the discrepancy between warm sea surface temperatures and cold terrestrial conditions reconstructed with other proxies for this time period

late pleistocene piedmont glaciations in the eastern mediterranean insights from cosmogenic 36cl dating of hummocky moraines in southern turkey abstract we report the presence of late pleistocene piedmont glaciers represented by the largest hummocky moraine field observed in the eastern mediterranean the piedmont glaciers originated from the geyikdag ice cap 40 km 2 situated between 2350 and 2650 m above sea level a s l central tauride mountains of turkey and deeply carved the north facing hillslopes before reaching the namaras valley 2000 2050 m a s l the hummocky moraines resulted from in situ deposition of stagnant glacier ice where debris cover was heterogeneously distributed on the glacier surface thirty four boulders from hummocky disintegration lateral and terminal moraines from the namaras valley and the tributary susam valley 2100 2200 m a s l were dated by cosmogenic 36 cl surface exposure dating the moraine ages indicate three phases of deglaciation during the late pleistocene the oldest deglaciation occurred in the namaras valley at 18 0 1 1 ka ka thousand years ago towards the end of the last glacial maximum lgm and is recorded entirely by hummocky moraines we speculate that hummocky moraine forming processes with cycles of relief inversion gave rise to boulder apparent ages up to a few thousand years younger in our study area therefore 18 0 1 1 ka should be regarded as a minimum age with a probable true age much closer to the local lgm values 20 ka as observed in the surrounding mountains paleo piedmont glaciers also deposited several lateral moraines that are 50 m higher than the hummocky moraines although the lateral moraines probably represent the build up and the hummocky moraines the final phase of the same local lgm pulse both lateral moraines started to retreat from the late glacial 14 0 2 7 ka and gradually disappeared by mid holocene 5 2 1 0 ka encompassing the younger dryas yd stadial in the susam valley the late glacial is represented by a terminal moraine 13 4 1 5 ka the glacier retreat was very fast as indicated by an almost instantaneous disappearance of 5 km long susam valley glacier represented by disintegration and hummocky moraines 14 0 1 3 ka alternatively in case the oldest boulder age is taken into account the susam valley glacier can be also attributed to the late lgm 17 ka to late glacial 14 ka transition near the exit of the susam valley a right lateral moraine was deposited 11 6 1 3 ka ago confirming the presence of the yd in geyikdag comparable glacial chronologies were obtained from other turkish and mediterranean mountains

coastal vulnerability analysis during tsunami induced levee overflow and breaching by a high resolution flood model abstract the coastal levee is a crucial defense element in low lying coastal areas but is vulnerable to overflow when water levels increase extremely this study focuses on the failure of the concrete armored levees caused by local scouring at the toe of their landward slope that was widely observed in the 2011 tohoku tsunami in japan using a high resolution flood model with a shock capturing property we explore the actual breach processes and their impacts on the protected areas in one of the most devastated districts the model is based on nonlinear shallow water equations and successfully reproduces detailed flow structures of the tsunami overflow at 2 m resolution however because we neglect the non hydrostatic pressure over steep levee slopes the modeled overflow discharge is slightly underestimated during simulation supercritical flow developed on the land side of levee sections with slowly rising tailwater water level due to hinterland topographic features despite the large overflow discharge topographic data analysis revealed large scale scour holes or trenches at the locations of the supercritical flow development suggesting that levee vulnerability can be identified by the local flow parameters based on the high resolution model the levee breach was modeled as a sudden removal of the corresponding levee section and the consequences were investigated the levee breach changed the spatial balance of the flood intensity but did not significantly worsen the damage in this case because the narrow low lying areas were fully inundated even without breach

temperature and precipitation in the southern central andes during the last glacial maximum heinrich stadial 1 and the younger dryas abstract recent developments in terrestrial cosmogenic nuclide tcn exposure dating and the reinterpretation of tcn boulder ages from moraines have improved our understanding of the glacial chronology in the central andes according to these records glacial advances throughout the region correlate with insolation driven changes in the intensity of the south american summer monsoon and millennial scale climate events such as heinrich stadials and the younger dryas quantifying the temperature and precipitation shifts during these events helps to constrain past moisture pathways and associated changes in atmospheric circulation patterns yet particularly in the southern central andes where a wealth of glacigenic landforms attests to formerly cooler and or wetter conditions the magnitudes of past temperature and precipitation changes are only loosely constrained at a few sites here we present results from tcn dated moraines combined with the reconstruction of former glaciers and paleolakes within the eastern sector of the southern central andes 24 27 s for the last glacial maximum lgm heinrich stadial 1 hs1 and the younger dryas yd we performed monte carlo simulations with 2 dimensional models of ice flow and lake hydrology that are forced by a spatially distributed surface energy balance model our results indicate that temperatures were 3 0 4 2 c 2 0 3 3 c and 1 3 2 5 c cooler during the lgm hs1 and yd respectively in agreement with previous estimates elsewhere in the central andes we find that temperature changes during the late glacial are compatible with sea surface temperature anomalies derived from the tropical atlantic precipitation was only 5 27 greater than today which contrasts with larger anomalies reconstructed for the bolivian part of the andean plateau altiplano we attribute this discrepancy to the southerly position of our study region with respect to the bolivian high supporting the hypothesis that this atmospheric pressure system played a prominent role for south american summer monsoon dynamics during glacial episodes

late quaternary glacier advances and palaeolake highstands in the bolivian altiplano abstract recent study of late quaternary moraines and pluvio lacustrine features around the southern altiplano of bolivia suggests they developed more or less synchronously during the last glacial cycle the stratigraphy of lacustrine and deltaic sediments can be linked to outwash and moraines on glaciated massifs e g cerro condor iquina cerro azanaques and cerro tunupa which border the poopo uyuni and coipasa salt basins uranium series and radiometric dating of lake carbonates by previous workers suggests that major palaeolakes developed during the intervals 72 68 ka bp 44 34 ka bp and 15 4 9 5 ka bp radiocarbon dating of peat associated with glacifluvial and glacial sediments indicates that the most extensive glacier advance of the later part of the last glacial cycle culminated after 13 3 ka bp and that a smaller readvance may have occurred between 12 and 10 ka bp as the highest palaeolake stand the tauca phase has been dated to ca 13 8 ka bp it is concluded that increased effective moisture and cool climatic conditions during the interval ca 14 13 ka bp forced the simultaneous expansion of glaciers and lakes in and around the southern altiplano a palaeolake may have been present on the southern altiplano for much of the interval ca 15 4 9 5 ka bp its surface reaching different levels at different times

discharge coefficient of a trapezoidal broad crested side weir for low approach froude numbers abstracteven though broad crested side weirs have been subjected to numerous studies guidance for discharge coefficient determination for broad crested side weirs still has not been clearly given experimental research was carried out to describe the flow conditions in front of a trapezoidal broad crested side weir at low froude numbers in the approach channel for various combinations of inflow and overflow discharges three side weir variants with different oblique angles were studied flow characteristics at the side weir were analyzed and assessed based on the results obtained from extensive measurements performed on a hydraulic model the empirical relation between the coefficient of obliqueness the angle of side weir obliqueness and froude numbers upstream and downstream of the weir was derived

isotopic age constraints on middle paleozoic deformation in the northern sierra nevada california allochthons of the lower paleozoic shoo fly complex in the northern sierra nevada were assembled and internally deformed prior to formation of a devonian permian island arc sequence u pb data on zircons indicate ages of 423 5 15 ma for a submarine tuff within the uppermost thrust slice of the shoo fly complex and 378 5 10 ma for a granitic intrusion that may be cogenetic with the lower part of the arc sequence these data indicate late early silurian shoo fly deposition and proximity to active volcanism as well as late middle devonian initiation of arc related magmatism

the glaciogenic origin of the pleistocene calcareous dust in argentina on the basis of field mineralogical textural and geochemical analyses calcareous dust occurs in argentina as layers and pockets closely associated with pleistocene deposits and periglacial features from southernmost patagonia to at least the mendoza precordillera and has been traditionally interpreted as a soil horizon resulting from postdepositional pedogenesis during interglacials detailed field and microscopic observations and sedimentological and geochemical analyses of more than 100 samples collected from lower to upper pleistocene deposits between 51 s and 33 s and from near sea level to 2800 m asl allow us to interpret the dust as synchronous with the host sediment all observations and analyses lead us to conclude that 1 the cryogenic morphology and the chemical signatures of the calcite component show that the dust is glaciogenic 2 the dust was carried by southeasterly antarctic winds and 3 it was deposited over most of southern and central argentina field observations geomorphic evidence and radiocarbon dates suggest that the dust was deposited during several pleistocene glacial episodes