petrographic features of tills as a tool in solving stratigraphical and palaeogeographical problems a case study from central eastern poland abstract lithostratigraphical correlation of tills in poland is most often carried out on the basis of petrographic analysis of fine gravel fraction 20 mm of tills from central eastern poland samples were taken in the sites the stratigraphy of which was previously well recognized based on the proportions between erratics derived from different regions of fennoscandia and their calculated theoretical boulder centres two main lithotypes of tills of middle pleistocene age are distinguished a and b lithotype a is assigned to elsterian the south polish complex sanian 2 mis 12 lithotype b is considered to be characteristic of saalian the middle polish complex within litothype b there are distinguished two sublithotypes b 1 and b 2 which can be linked to the advances of fennoscandian ice sheet during mis 8 older saalian and mis 6 younger saalian the results of the research reveal that the changes of erratics assamblages in tills deposited during the successive ice sheet advances in central eastern poland reproduce a trend that has been ascertained earlier in the sites located approx 200 km further west in central poland and 600 km in northern germany where their stratigraphic position is not so clear cut the general trend of changes in all three areas is the same but the petrographic composition of tills of the same age varies along the former glacier front the results indicate the advisability of using a modified more appropriate methodology in the analysis of indicator erratics occurring in tills we recommend that the calculation of theoretical boulder centres tbc should be based only on crystalline igneous and metamorphic erratics they are strongly resistant ones therefore the lithostratigraphic correlation of tills of various weathering degree is more reliable

the genesis of severe long lived bow echoes abstract a series of idealized simulations using a nonhydrostatic cloud model is used to investigate the genesis of bow echoes a bow shaped system of convective cells that is especially noted for producing long swaths of damaging surface winds it is hypothesized that severe long lived bow echoes represent a dynamically unique form of mesoconvective organization being produced for a restricted range of environmental conditions including a convective available potential energy cape of at least 2000 m2 s2 and vertical wind shears of at least 20 m s 1 over the lowest 2 5 5 km agl the key structural features include a 40 100 km long bow shaped segment of convective cells with a strong rear inflow jet extending to the leading edge of the bow at 2 3 km agl and cyclonic and anticyclonic eddies referred to as bookend vortices on the northern and southern flanks of the bowed segment respectively this structure characteristically develops three to four hours into the lifetime of a convective system a

bow echo mesovortices part ii their genesis abstract this two part study examines the damaging potential and genesis of low level meso scale mesovortices formed within bow echoes this was accomplished by analyzing quasi idealized simulations of the 10 june 2003 saint louis bow echo event observed during the bow echo and mesoscale convective vortex experiment bamex in part ii of this study mesovortex genesis was investigated for vortices formed at different stages of convective system evolution during the early cellular stage cyclonic mesovortices were observed the cyclonic mesovortices formed from the tilting of baroclinic horizontal vorticity acquired by downdraft parcels entering the mesovortex as the convective system evolved into a bow echo cyclonic anticyclonic mesovortex pairs were also observed the vortex couplet was produced by a local updraft maximum that tilted baroclinically generated vortex lines upward into arches the local updraft maximum was created by a convective scale downdraft that produced an outward bulge in th

bow echo mesovortices part i processes that influence their damaging potential abstract this two part study examines the damaging potential and genesis of low level meso scale mesovortices formed within bow echoes this was accomplished by analyzing quasi idealized simulations of the 10 june 2003 saint louis bow echo event observed during the bow echo and mesoscale convective vortex experiment bamex this bow echo produced both damaging and nondamaging mesovortices a series of sensitivity simulations were performed to assess the impact of low and midlevel shear cold pool strength and coriolis forcing on mesovortex strength by analyzing the amount of circulation maximum vertical vorticity and number of mesovortices produced at the lowest grid level it was observed that more numerous and stronger mesovortices were formed when the low level environmental shear nearly balanced the horizontal shear produced by the cold pool as the magnitude of deeper layer shear increased the number and strength of mesovortices increased larger coriolis forcing and stronger cold pools als

a multiproxy study of a basal till a time transgressive accretion and deformation hypothesis a two part basal till at knud strand denmark reveals a uniform fabric pattern and strength petrographical composition and clay mineralogy the nature of the contact with the underlying sediments ductile deformation structures partly intact soft sediment clasts small meltwater channels and thin horizontal outwash stringers dispersed in the till indicate both bed deformation and basal decoupling by pressurised subglacial water a time transgressive model is suggested to explain the lack of vertical gradation in till properties in which debris released from the active ice sole is sheared in a thin zone moving upward as till accretion proceeds it is suggested that although strain indicators occur throughout the entire till thickness the deformation at any point of time encompassed the uppermost part of the till only allowing preservation of fragile clasts below the substantial thickness of the till up to 6 m coupled with a much smaller by more than one order of magnitude inferred thickness of the deforming bed suggests that the bulk of till material was transported englacially prior to deposition the lack of petrographical gradation in the till is attributed to effective mixing and homogenisation of material along the ice flow path copyright 2004 john wiley sons ltd

high winds generated by bow echoes part i overview of the omaha bow echo 5 july 2003 storm during bamex abstract an analysis of a bow echo that produced damaging winds exceeding f1 in intensity on the fujita scale near omaha nebraska is shown part i of this study presents a combination of airborne doppler derived wind syntheses with a comprehensive damage survey in order to document the generation of strong winds at the surface a detailed kinematic analysis of the evolution of a quasi linear convective system into a bow shaped and subsequently a spearhead echo is shown for the first time it is hypothesized that a large cyclonic bookend vortex 70 80 km in diameter north of the bow apex enhanced the rear inflow jet and initiated the bowing process a hook shaped echo and mesovortex formed at the apex of a bowed segment of the convective line and was located to the north of the swath of strong damage rated greater than f1 in damage intensity the peak single doppler radial velocity recorded by the tail radar was 43 m s 1 in the low level outflow near the apex of the bow echo the regions of the str

structure and evolution of a severe squall line over oklahoma abstract a squall line on 2 may 1979 developed in oklahoma in proximity to a synoptic scale cold front this line is analyzed during its growth and mature periods using radar satellite sounding and surface data some of the cells produced hail and many of the cell tops reached 16 km however there were no reports of tornadoes three main topics are addressed in the paper 1 examination of squall line and cell propagation mechanisms 2 the three dimensional structure of the squall line and individual cells during the mature period and 3 mass and moisture fluxes and precipitation efficiency comparison is made between the 2 may case and other tropical and midwest squall line cases the 2 may case does not exhibit a trailing stratiform anvil during the period mechanism requiring veering environmental wind shear in the lowest levels and 2 mechanism where the cell motion is eventually governed by the moisture convergence and lifting provided the convergence line the motion of the squall line defin

low level mesovortices within squall lines and bow echoes part i overview and dependence on environmental shear this two part study proposes fundamental explanations of the genesis structure and implications of lowlevel meso g scale vortices within quasi linear convective systems qlcss such as squall lines and bow echoes such mesovortices are observed frequently at times in association with tornadoes idealized simulations are used herein to study the structure and evolution of meso g scale surface vortices within qlcss and their dependence on the environmental vertical wind shear within such simulations significant cyclonic surface vortices are readily produced when the unidirectional shear magnitude is 20 m s 21 or greater over a 0 2 5 or 0 5 km agl layer as similarly found in observations of qlcss these surface vortices form primarily north of the apex of the individual embedded bowing segments as well as north of the apex of the larger scale bow shaped system they generally develop first near the surface but can build upward to 6 8 km agl vortex longevity can be several hours far longer than individual convective cells within the qlcs during this time vortex merger and upscale growth is common it is also noted that such mesoscale vortices may be responsible for the production of extensive areas of extreme straight line wind damage as has also been observed with some qlcss surface vortices are also produced for weaker shears but remain shallow weak and short lived although similar in size and strength to mesocyclones associated with supercell storms and also sometimes producing similar hooklike structures in the rain field it is also shown that the present vortices are quite distinct structurally and dynamically most critically such vortices are not associated with long lived rotating updrafts at midlevels and the associated strong dynamically forced vertical accelerations as occur within supercell mesocyclones

till stratigraphy and sedimentology at the margins of terrestrially terminating ice streams case study of the western canadian prairies and high plains complex glacigenic sediment sequences arranged in large arcuate assemblages and demarcating the lobate termini of fast ice flow corridors in western canada represent the terrestrial equivalents of the trough mouth fans of the marine palaeo ice stream record intensive sedimentological and stratigraphic investigations at a regional scale are employed in the interpretation of thick units or sequences of diamicton and two depositional scenarios are proposed first glacier marginal till thickening and the stacking of till wedges takes place in areas where an ice stream margin was stationary for short periods of time stacks of subglacial traction tills potentially record annual sub marginal incremental thickening at ice stream margins especially in areas where densely spaced recessional push moraines appear to record seasonal climatic forcing second proglacial lake and valley infilling with glacilacustrine rhythmites and mass flow diamictons is associated with the advection of sub marginal till into preglacial bedrock depressions and records ice stream marginal oscillations and debris influx into discontinuous proglacial lakes which act as subaqueous sediment sinks for materials that would otherwise have been used to construct sub marginal till wedges and moraines glacial overriding modifies the deposits produced in both scenarios through deformation and the dislocation and entrainment of bedrock and sediment rafts at the margins of bedrock valley walls resulting in the widespread development of glacitectonites and megablocks the occurrence of the thickest deposits as preglacial valley fills may be significant in groundwater siphoning away from subglacial deforming layers and the promotion of sticky spots

formation of subglacial till under transient bed conditions deposition deformation and basal decoupling under a weichselian ice sheet lobe central poland a multi proxy approach involving a study of sediment architecture grain size grain roundness and crushing index petrographic and clay mineral composition till fabric and till micromorphology was applied to infer processes of till formation and deformation under a weichselian ice sheet at kurzetnik poland the succession consists of three superposed till units overlying outwash sediments deformed at the top the textural characteristics of tills vary little throughout the till thickness whereas structural appearance is diversified including massive and bedded regions indicators of intergranular bed deformation include overturned attenuated folds boudinage structures a sediment mixing zone grain crushing microstructural lineations grain stacking and high fabric strength lodgement proxies are grooved intra till surfaces ploughing marks and consistently striated clast surfaces basal decoupling by pressurized meltwater is indicated by undisturbed sand stringers sand filled meltwater scours under pebbles and partly armoured till pellets it is suggested that the till experienced multiple transitions between lodgement deformation and basal decoupling cumulative strain was high but the depth of time transgressive deformation much lower centimetre range than the entire till thickness ca 2 m at any point in time consistent with the deforming bed mosaic model throughout most of ice overriding porewater pressure was high in the vicinity of glacier floatation pressure indicating that the substratum consisting of 11 m thick sand was unable to drain subglacial meltwater sufficiently

the late weichselian glacial record in northern poland a new look at debris transport routes by the fennoscandian ice sheet abstract the area of the kashubian coastland and areas adjacent to the northern part of the lower vistula valley northern poland were involved in the major transgressive phases distinguished in poland during the late weichselian due to the small scale of the regressions between the different phases of the late weichselian the ice sheet usually deposited only one till but with a complex vertical profile based on the studies of the directional properties petrographic composition of the fine gravel fraction and the analysis of indicator erratics the dichotomy of the till bed was demonstrated the petrographic composition of the gravel fraction in tills together with the analysis of the indicator erratics and delimitation of the theoretical boulder centres were used to determine the direction of the influx of ice masses this allowed speculation on the reasons for the different dynamics of the fennoscandian ice sheet fis as well as the operation and time variability of the baltic ice stream bis it was emphasised that the delivery system of debris by the ice sheet might have been complex and multidirectional more than one route it has been suggested that changes in the petrographic composition of the gravel fraction of the glacial sediments did not have to be associated only with shifting the centre of glaciation but may have resulted from a change in the thermal regime of the ice sheet s bed in the source area especially with the spread of the cold regime zone and depended on the dynamics of the ice sheet stream or sheet flow as well as the spatial and temporal conditions of its development in the deposition area

an outline of the pleistocene stratigraphy of the kleszczow graben bechatow outcrop central poland abstract the pleistocene sequence of the kleszczow graben central poland is located in a brown coal quarry 8 km long and 4 km wide it contains ten separate organic horizons in part stacked one above another and in part correlated by reference to associated inorganic units using heavy minerals and gravel petrography three of the organic horizons represent interglacials ferdynandovian mazovian holsteinian and eemian others represent interstadial or periglacial deposits the tertiary quaternary boundary is recorded at the site by reuverian c and prae tiglian biostratigraphy occurring in a single section a major hiatus exists above the prae tiglian and lower pleistocene and cromerian deposits are absent glacial deposits are represented by three elsterian tills five saalian tills and glaciofluvial and glaciolacustrine deposits the czyzow formation lies between the elsterian and saalian deposits and contains at least two interglacials the ferdynandovian and mazovian and several interstadial units without glacial intervening deposits the lower saalian odranian drenthe deposits are separated from the middle saalian wartanian 1 by fluvial sands and organic deposits of the pilica interstadial the middle wartanian 1 and upper saalian wartanian 2 also may be separated by an interstadial palaeosol the evidence from the kleszczow graben supported by other central european quaternary sequences suggest that only four glaciations occurred within the region during the middle pleistocene and that these glaciations were separated by long periods with a complex climate ranging from temperate to periglacial

steppe mammoth mammuthus trogontherii remains in their geological and cultural context from belchatow poland a consideration of human exploitation in the middle pleistocene abstract in 1981 and 1991 mammoth remains and associated fauna were found in central poland at the belchatow opencast mine in sandy gravel deposits most of them lay at approximately 160 175 m above mean sea level a s l located in the lower and upper members of the alluvial chojny formation this formation belongs to the middle pleistocene and can be connected with the mazovian mis 11 holsteinian or zbojnian mis 9 reinsdorf interglacial the belchatow mammoth assemblage described here consists of cranial and postcranial elements analysis of their morphological characteristics and osteometrics are used to demonstrate that at least two molars and one tusk belong to mammuthus trogontherii and that the tusk belonged to a male on the basis of the minimum number of elements of the most common element left incisors the mammoth remains represent at least two individuals based upon the different ages of death for the various elements it appears that they represent several individuals the bulk of the mammoth remains were recovered from the oldest depositional cycle in the lower member of chojny formation and are therefore coincident with a shrub tundra environment and cool temperate conditions they were deposited in sediments formed by a meandering river with a fairly low power of flow and were buried soon after transport over a short distance this conclusion is also supported by the palaeobotanical data an additional element a costa was recovered from the upper member of the chojny formation which is associated with the cooling conditions the enveloping deposit appears to be the result of a series of more rapid discharge events by a braided river this element is distinguished from those elements recovered from the lower member due to the presence of a series of unusual striations sem analysis suggests that some of the striations were probably made by chipped stone tools used in a slicing action as if the result of the filleting of flesh from the rib area the time frame for the depositional context of the costa suggests that the striations may have been made by one of several possible human taxa that occurred in central europe during this period including homo heidelbergensis given the dearth of human skeletal remains from this region and time period this represents the earliest and only example of middle pleistocene human butchering activity in poland the remains discussed in this paper are presented in light of their depositional and cultural contexts which not only increases our knowledge of the occurrence of m trogontherii in poland but also provides increased evidence for lower palaeolithic human activity in central europe during an early interglacial

landform and sediment imprints of fast glacier flow in the southwest laurentide ice sheet evidence for former fast glacier flow ice streaming in the southwest laurentide ice sheet is identified on the basis of regional glacial geomorphology and sedimentology highlighting the depositional processes associated with the margin of a terrestrial terminating ice stream preliminary mapping from a digital elevation model of alberta identifies corridors of smoothed topography and corridor parallel streamlined landforms megaflutes to mega lineations that display high levels of spatial coherency ridges that lie transverse to the dominant streamlining patterns are interpreted as a series of minor recessional push moraines b thrust block moraines or composite ridges hill hole pairs constructed during readvances surges and c overridden moraines cupola hills apparently of thrust origin together these landforms demarcate the beds and margins of former fast ice flow trunks or ice streams that terminated as lobate forms localised cross cutting and or misalignment of flow sets indicates temporal separation and the overprinting of ice streams lobes the fast flow tracks are separated by areas of interlobate or inter stream terrain in which moraines have been constructed at the margins of neighbouring competing ice streams outlet glaciers this inter stream terrain was covered by more sluggish non streaming ice during full glacial conditions thin tills at the centres of the fast flow corridors in many places unconformably overlying stratified sediments suggest that widespread till deformation may have been subordinate to basal sliding in driving fast ice flow but the general thickening of tills towards the lobate terminal margins of ice streams outlet glaciers is consistent with subglacial deformation theory in this area of relatively low relief we speculate that fast glacier flow or streaming was highly dynamic and transitory sometimes with fast flowing trunks topographically fixed in their onset zones and with the terminus migrating laterally the occurrence of minor push moraines and flutings and associated landforms because of their similarity to modern active temperate glacial landsystems are interpreted as indicative of ice lobe marginal oscillations possibly in response to seasonal climatic forcing in locations where meltwater was more effectively drained from the glacier bed further north the occurrence of surging glacier landsystems suggests that persistent fast glacier flow gave way to more transitory surging possibly in response to the decreasing size of ice reservoir areas in dispersal centres and also locally facilitated by ice bed decoupling and drawdown initiated by the development of ice dammed lakes copyright 2008 john wiley sons ltd

the role of convectively generated rear inflow jets in the evolution of long lived mesoconvective systems abstract in this study the structure of convectively generated rear inflow jets and their role in the evolution of long lived mesoconvective systems are investigated through an analysis of idealized three dimensional simulations using a nonhydrostatic cloud model rear inflow jets are generated within these systems in response to the upshear tilting of the convective circulation as the horizontal buoyancy gradients along the back edge of the expanding system create a circulation that draws midlevel air in from the rear within this framework a wide range of rear inflow strengths and structures are produced depending on the magnitude of the ambient convective available potential energy cape and the vertical wind shear in general for environments characterized by weak to moderate vertical wind shear and weak to moderate cape the rear inflow jet descends and spreads along the surface well behind the leading edge of the gust front and the subsequent convective activity becomes weaker however for e

dynamics of the north american ice sheet complex during its inception and build up to the last glacial maximum the north american ice sheet complex played a major role in global sea level fluctuations during the late quaternary but our knowledge of its dynamics is based mostly on its demise from the last glacial maximum lgm a period characterised by non linear behaviour in the form of punctuated ice margin recession episodic ice streaming and major shifts in the location of ice divides in comparison knowledge of the pre lgm ice complex is poorly constrained largely because of the fragmentary nature of the evidence relating to ice sheet build up in this paper we explore the inception and growth of ice 120 20 ka using a glacial systems model which has been calibrated against a large and diverse set of data relating to the deglacial interval we make use of calibration data prior to the lgm but its scarcity introduces greater uncertainty which is partly alleviated by our large ensemble analysis results suggest that following the last interglaciation oxygen isotope stage ois 5e the ice complex initiated over the north eastern canadian arctic and in the cordillera within a few thousand years it then underwent rapid growth to an ois 5 maximum at 110 ka 5d and covered 70 of the area occupied by the lgm ice cover although only 30 by volume an ois 5 minimum is modelled at 80 ka 5a before a second phase of rapid growth at the start of ois 4 which culminated in a large ice complex at 65 ka almost as large as at the lgm subsequent deglaciation was rapid maximum modelled sea level contribution of 16 cm per century and resulted in an ois 3 minimum between ca 55 60 ka thereafter the ice complex grew towards its lgm configuration interrupted by several phases of successively less significant mass loss our results support and extend previous inferences based on geological evidence and reinforce the notion of a highly dynamic pre lgm ice complex e g with episodes of 10 s m of eustatic sea level equivalent in 50 but even the thin ois 5 ice sheets exhibit fast flow features several 1000 m a 1 in major topographic troughs notwithstanding the severe limitations imposed by the use of the shallow ice approximation we note that most fast flow features generated prior to the lgm correspond to the location of known ice streams during deglaciation i e in major topographic troughs and over soft sediments at the southern and western margins moreover the modelled flux of these ice streams sensu lato appears to be non linearly scaled to ice sheet volume i e there is no evidence that decay phases were associated with significantly increased ice stream activity this hypothesis requires testing using a model with higher order physics and future modelling would also benefit from additional pre lgm constraints e g dated ice free margin positions to help reduce and quantify uncertainties

palaeoglaciology of an ice sheet through a glacial cycle the european ice sheet through the weichselian abstract satellite images provide unique means of identifying large scale flow generated lineations produced by former ice sheets they can be interpreted to reconstruct the major elements which make up the integrated large scale structure of ice sheets ice divides ice streams interstream ridges ice shelves calving bays the evolving palaeoglaciological structure of the european ice sheet during its decay from the last glacial maximum lgm is reconstructed by reference to these components and in the context of a new map showing isochrons of retreat during the retreat phase in particular the time dependent dynamic evolution of the ice sheet and the pattern of ice stream development are reconstructed crossing lineations are widespread the older ones are suggested to have formed during molten bed phases of ice sheet growth and preserved by frozen bed conditions during the glacial maximum particularly in areas which lay during deglaciation beneath ice divides and inter ice stream ridges both areas of slow flow and possibly frozen bed conditions four phases of growth a1 to a4 and five phases of decay r1 to r5 are used to describe the major climatically and dynamically determined stages in the evolution of the ice sheet through the last glacial cycle the growth and decay patterns are quite different and associated with major shifts in the ice divide reflecting growth from the fennoscandian mountains and decay away from marine influenced margins these patterns were determined by the locations of nucleation areas spatial patterns of climate and calving at marine margins the prevalence of streaming within the retreating ice sheet suggests that the mean elevation of the ice sheet was lower than predicted from glaciological models which do not include streaming and that this might reconcile glaciological models and earth rheology models which infer paleao ice sheet thickness by inverting sea level data

the geology of the southeastern baltic sea a review the baltic sea particularly its southeastern part is discussed in the paper investigations of regional character as well as specialized studies in the area are reviewed general historical works

evolution of a quasi linear convective system sampled by phased array radar abstracton 2 april 2010 a quasi linear convective system qlcs moved eastward through oklahoma during the early morning hours wind damage in rush springs oklahoma approached enhanced fujita ef1 scale intensity and was likely associated with a mesovortex along the leading edge of the qlcs the evolution of the qlcs as it produced its first bow echo was captured by the national weather radar testbed phased array radar nwrt par in norman oklahoma the nwrt par is an s band radar with an electronically steered beam allowing for rapid volumetric updates 1 min and user defined scanning strategies the rapid temporal updates and dense vertical sampling of the par created a detailed depiction of the damaging wind mechanisms associated with the qlcs key features sampled by the par include microbursts an intensifying midlevel jet and rotation associated with the mesovortex in this work par data are analyzed and compared to data from nearby operational radars highlighting the advantages of using

climatostratigraphy of interglacials in poland middle and upper pleistocene lower boundaries from a polish perspective abstract the brunhes matuyama paleomagnetic boundary has been identified in some key interglacial sites in poland helping in interpret the results of many years climatostratigraphic research the major qualitative stratigraphic boundary is located at the onset of the mazovian interglacial holsteinian that separates the older composite from the younger simple interglacials the two composite interglacials comprise 2 3 interglacial rank warmings each separated by profound but non glacial coolings the four simple interglacials mazovian interglacial included are expressed by single warmings only each interglacial possesses a characteristic pollen succession and the successive interglacials are interbedded with tills of the scandinavian provenance simple interglacials are typical of mis 11 1 and reflect a climate system predominated by 100 ka orbital cycles composite interglacials are characteristic of the interval mis 22 12 and reflect a transition from a climate system predominated by 41 ka orbital cycles to 100 ka cycles i e the mid pleistocene revolution based on these general differences the mis 23 22 and mis 12 11 boundaries are recommended as key thresholds during the pleistocene and could be reconsidered as the lower boundaries of middle and upper pleistocene respectively

terrestrial ice streams a view from the lobe abstract the glacial landforms of minnesota are interpreted as the products of the lobate extensions of ice streams that issued from various ice sheds within the laurentide ice sheet low relief till plains trough shaped lowlands boulder pavements and streamlined forms make up the subglacial landsystem in minnesota that is interpreted as having been formed by streaming ice extremely uniform tills are created subglacially in a way that remains somewhat mysterious at the ice margins thrust moraines and hummocky stagnation topography are more common than single crested simple moraines if the ice lobes had repeated advances subglacial drainage features are obscure up ice but are present down ice in the form of tunnel valleys eskers spooner hills and associated ice marginal fans ice streaming may occur when basal shear stress is lowered as a result of high subglacial water pressure subglacial conditions that allow the retention of water will allow an ice lobe to extend far beyond the ice sheet as long as the ice shed also supports the advance by supplying adequate ice even with adequate ice flux however the advance of an ice lobe may be terminated at least temporarily if the subglacial water is drained through tunnel valleys or perhaps a permeable substrate thrust moraines and ice stagnation topography will result from sudden drainage although climate change is ultimately responsible for the accumulation of ice in the laurentide ice sheet the asynchronous advances and retreats of the ice lobes in the mid continent are strongly overprinted by the internal dynamics of individual ice streams as well as the interaction of ice sheds which obscure the climate signal

fennoscandian palaeoglaciology reconstructed using a glacial geological inversion model the evolution of ice sheet configuration and flow pattern in fennoscandia through the last glacial cycle was reconstructed using a glacial geological inversion model i e a theoretical model that formalises the procedure of using the landform record to reconstruct ice sheets the model uses mapped flow traces and deglacial melt water landforms as well as relative chronologies derived from cross cutting striae and till lineations as input data flow trace systems were classified into four types i time transgressive wet bed deglacial fans ii time transgressive frozen bed deglacial fans iii surge fans and iv synchronous non deglacial event fans using relative chronologies and aggregation of fans into glaciologically plausible patterns a series of ice sheet configurations at different time slices was erected a chronology was constructed through correlation with dated stratigraphical records and proxy data reflecting global ice volume geological evidence exists for several discrete ice sheet configurations centred over the scandinavian mountain range during the early weichselian the build up of the main weichselian fennoscandian ice sheet started at approximately 70 ka and our results indicate that it was characterised by an ice sheet with a centre of mass located over southern norway this configuration had a flow pattern which is poorly reproduced by current numerical models of the fennoscandian ice sheet at the last glacial maximum the main ice divide was located overthe gulf of bothnia a major bend in the ice divide was caused by outflow of ice to the northwest over the lowest part of the scandinavian mountain chain widespread areas of preserved pre late weichselian landscapes indicate that the ice sheet had a frozen bed core area which was only partly diminished in size by inward transgressive wet bed zones during the decay phase

non supercell tornadoes abstract analyses of tornadoes that are not associated with supercells are presented the database for this study was collected during cinde convention initiation and downburst experiment a field project operated during the summer of 1987 in colorado a total of 27 visual vortices were studied they appeared to form as shear instabilities along radar detected convergence lines the circulations initiated at low levels generally in the absence of precipitation echo subsequently as these vortices propagated along the convergence line they appeared to strengthen to tornadic intensity when they became colocated with the updraft of a rapidly developing storm it is hypothesized that vortex stretching is responsible for intensifying the initial rotation although these tornadoes were weaker than those accompanied by strong midlevel mesocyclones estimates of their strength suggest damage capability as high as f2 the implications for operational radars to detect these types of phenomena were identified the

rear inflow in squall lines with trailing stratiform precipitation abstract the relative airflow and accompanying precipitation structure of squall lines trailed by mesoscale regions of stratiform rain are examined with emphasis on the occurrence of rear inflow i e the intrusion of environmental air into these storms across the trailing precipitation boundary three cases from kansas and oklahoma provide examples of strong rear inflow which crosses the back edge of the stratiform precipitation area at relative speeds exceeding 10 m s 1 the vertical profiles of relative flow at the trailing precipitation boundary of these three systems were remarkably similar with the rear inflow confined to a jet like layer centered at about 550 mb doppler radar data for two of these cases showed that the rear inflow jet occupied a continuous channel extending from middle levels at the back edge of the stratiform region to lower levels of the leading convective region where it merged with outflow from convective downdrafts to bolster the leading gust front strong front to rea

geometry of a miocene submarine canyon and associated sedimentary facies in southeastern calabria southern italy outcrops of the stilo capo d9orlando formation latest oligocene early miocene along the southeastern coast of calabria southern italy expose a cross section orthogonal to paleoflow of the proximal part of a turbidite depositional system major erosion surfaces cutting into basement rocks define several submarine paleocanyons paleocanyon fills consist of large lenticular conglomerate bodies that are 200 580 m thick and 3 6 km wide the best example of these paleocanyons is located near the town of stilo where the geometric relationships between paleocanyon fill and adjacent slope deposits are well exposed at this locality a 460 m thick section of conglomerate cuts into the basement and is composed internally of smaller scale channel fills of poorly organized clast supported cobble to boulder conglomerate deposited mainly by high density turbidity flows the conglomerate is thickest near stilo and becomes progressively thinner southward where a wedge of mudrock intervenes between the basement and the conglomerate the mudrock wedge is composed of poorly bedded intensely bioturbated mudstone with slump structures and represents slope deposits bedding within the mudrock wedge is better defined in its stratigraphically higher part near the conglomerate body where thin bedded normally graded sandstone layers with climbing ripples horizontal lamination and general thickening toward the canyon axis are present these layers are the deposits of dilute turbidity currents that occasionally spilled over the canyon margins when the depression was nearly filled the conglomeratic canyon fill and the adjacent muddy slope deposits are both overlain by a laterally continuous sequence 160 m thick composed of two units of fine grained thin bedded turbidites alternating with two units of thicker sandstone and minor pebble conglomerate beds the paleocanyons probably originated as subaerial valleys in response to a major fall in relative sea level at 30 ma and were later submerged by a combination of relative sea level rise and concomitant tectonic activity the sharp transition between coarse grained canyon confined conglomerate and the overlying fine grained unconfined thin bedded turbidites exists throughout southern calabria and may represent the effect of a significant rise in relative sea level two other cycles of relative sea level changes probably resulting from local tectonic control are indicated by the upper part of the stilo capo d9orlando formation

record of the vistula ice lobe advances in the late weichselian glacial sequence in north central poland during the last glacial maximum lgm the vistula ice lobe was one of the key morphological elements at the southern margin of the scandinavian ice sheet in north central poland the area of the vistula ice lobe experienced two ice sheet advances of varied extent the older one is correlated with the leszno brandenburg phase and the younger one is correlated with the poznan frankfurt phase sedimentological research and luminescence dating of the late weichselian glacial sequence in the vistula ice lobe area was conducted a new scenario of the late weichselian ice events in the area is presented the limit of the leszno phase within the vistula ice lobe was much smaller than had been accepted previously and its age is estimated to be about 20 300 bp significant ice sheet retreat was

large scale reorganization and sedimentation of terrestrial ice streams during late wisconsinan laurentide ice sheet deglaciation glacial geomorphological mapping of shuttle radar topography mission srtm data from the western canadian prairies demonstrates that during the last late wisconsinan deglaciation of the laurentide ice sheet terrestrial ice streams underwent a major reorganization of their flow configuration this reorganization involved a 90 shift in flow direction and was accompanied by a corresponding increase in the influence of topography on streaming flow ice streams included both topographically confined and pure ice streams that flowed independent of topography streaming flow is recorded by suites of highly elongate 60 km long subglacial bedforms bounded sharply at their lateral margins by prominent moraines initial streaming flow was unconfined by topography but was replaced progressively and crosscut by younger topographically confined flows flow reorganization is inferred to have been caused by temporal and spatial variations in the interaction between frozen and thawed bed conditions with thinning and shutdown of one ice stream ultimately triggering initiation of others this highlights the role of internal glaciodynamically driven reorganization in triggering streaming flow within large ice sheets and shows that large scale flow reorganization can occur over the time scale of a single deglaciation in terrestrial ice streams

laurentide glacial landscapes the role of ice streams glacial landforms of the north american prairie can be divided into two suites that result from different styles of ice flow 1 a lowland suite of level to streamlined till consistent with formation beneath ice streams and 2 an upland and lobe margin suite of thick hummocky till and glacial thrust blocks consistent with formation at ice stream and ice lobe margins southern laurentide ice lobes hypothetically functioned as outlets of ice streams broad branching lowlands bounded by escarpments mark the stable positions of the ice streams that fed the lobes if the lobes and ice streams were similar to modern ice streams their fast flow was facilitated by high subglacial water pressure favorable geology and topography in the midcontinent encouraged nonuniform ice flow and controlled the location of ice streams and outlet lobes

genesis of transverse kame trains in eastern poland abstract transverse kames forming trains perpendicular to the direction of ice sheet advance are rare morphological elements in previously glaciated areas the genesis of an example from the ice contact zone of the wartanian glaciation in eastern poland is discussed the transverse kames there form two main distinctly separated sub parallel trains their sedimentary successions fill erosional troughs incised in the pre wartanian deposits on northern slopes they consist of thick glaciofluvial sand and glaciofluvial glaciolacustrine sandy silty units that are covered with a thin usually discontinuous glacial till succession the genesis of this kame type has been modelled it is concluded that transverse kames developed in two phases 1 erosion of the substratum in subglacial channels during initial deglaciation and 2 glaciofluvial deposition in crevasses during advanced deglaciation in the form of low energy fans periodically submerged under stagnant water followed locally by a cover of flowtills both the ablation of the ice and the accumulation of the kame deposits were controlled by the co occurrence of ice zones either enriched or impoverished with sediment zonal enrichment of ice with debris was determined by the development of shear zones over substratum elevations that were inclined up ice the formation and subsequent infilling of crevasses both took place in zones of relatively clean ice so that the resulting kames form a train perpendicular to the direction of ice movement