hierarchies and spatial scale in process geomorphology a review abstract the form and functioning of a geomorphic system is the end product of a set of interacting processes which operate at a large variety of spatial and temporal scales an appreciation of the nested hierarchical structure of geomorphic systems offers insight into the effect of scale in process geomorphology a literature review led to the formulation of a series of propositions concerning the spatial scale problem in process geomorphology these propositions are presented in a theoretical framework indicating their association central to the spatial scale problem in process geomorphology is that a geomorphic system must be viewed in its complex hierarchicl context every geomorphic system consists of an array of ever smaller lower level systems and is at the same time part of a sequence of ever larger higher level system in a geomorphic system there exists a similarity between the scales of process and form furthermore within a geomorphic system there is a similarity between spatial and temporal scales so that the timespan to present system behaviour and morphology increases with system size in a geomorphic system differences occur in the sensitivity of morphology to changing process conditions depending on the time elapsed since a change in process conditions morphology in a geomorphic system may be either polygenetic when only partial adjustment of the morphology i e only at smaller scales has occurred or characteristic of the process domain when all aspects of morphology i e at all scales are adjusted to present process conditions in the latter case dominance of landscape evolution by high frequency low magnitude process results in a smooth landscape having small scale irregularities whereas dominance by low frequency high magnitude processes produces an irregular landscape having large scale irregularities when spatial scale is held constant the model of evolution of a geomorphic system varies with the timescale of interest conversely when temporal scale is held constant the model of evolution varies with the spatial scale of interest in both cases the canon fixed rules and options of a geomorphic system vary with the scale temporal or spatial of interest the linkages between spatial and temporal scale and between the scales of form and process of geomorphic systems lead to four additional points first whether or not an event is catastrophic depends on the hierarchical level of the geomorphic system second because of increased travel time and a larger variety of possible pathways differences between the temporal patterns and material properties of input and output increase with the hiirarchical level and scale of a geomorphic system third frequent small scale processes may cause infrequent large scale events when viewed at the same hierarchical level fourth and last differences between geomorphic systems at the same level are controlled by variables varying over distances equal to or smaller than the distance between the system but equal to or larger than the spatial dimensions of the systems

triassic jurassic boundary events inferred from integrated stratigraphy of the csővar section hungary abstract processes and causes of biotic and environmental change at the triassic jurassic transition remain controversial partly because of a scarcity of triassic jurassic boundary sections studied in detail continuous marine strata spanning the boundary are exposed at cs var hungary where new integrated stratigraphic data were obtained from multidisciplinary investigations to help reconstruct the end triassic and early jurassic events boundary strata are predominantly slope to basinal carbonates deposited in a periplatform basin the position of the system boundary is constrained by radiolarian foraminiferan conodont and ammonoid biostratigraphy pronounced radiolarian turnover is observed between assemblages assigned to the late rhaetian globolaxtorum tozeri zone and the early hettangian canoptum merum zone benthic foraminifera suffered lesser extinction successive conodont faunas of the latest rhaetian misikella posthersteini and misikella ultima zones record a marked drop in diversity and abundance but sporadic survivors persist into the earliest hettangian the extinction is also recorded in a reduction of biogenic components in carbonates decline of benthic and planktic biota is followed by a negative 13ccarb excursion of up to 6 that is composed of short term fluctuations revealed by dense sampling carbon and oxygen isotope ratios are positively correlated in the lower part of the section and appear to reflect primary variations drivers of the stable isotope trends are interpreted as warming in excess of 10 c and concomitant episodic short term perturbations of the global carbon cycle possibly due to methane release from gas hydrate dissociation induced by rapid climatic events the main biotic and isotopic events occurred within a single sedimentary cycle but sea level does not appear to have exerted a critical influence on these changes the triassic jurassic boundary crisis appears a short but not instantaneous event

regional and global changes around the triassic jurassic boundary reflected in the late norian hettangian history of the apennine basins abstract palaeogeographic restorations for the late triassic and early jurassic of the west mediterranean area show that significant facies changes occurred in this period the study of three basinal successions in the northern central and southern apennines indicates that changes in ecological conditions occurred at the same time in different palaeogeographic and geodynamic domains the early mesozoic evolution of the apennines is controlled by the opening of two oceans the ionian east mediterranean tethys to the south east and the alpine ocean to the north west the lagonegro basin in the southern apennines was the northern continental margin of the ionian tethys from the triassic while the la spezia basin in the northern apennines became part of the south eastern continental margin of the alpine ocean in the middle late jurassic the third studied basin mt camicia basin in the gran sasso central apennines was an intra platform basin from the early norian up to the late hettangian early sinemurian during the norian hettangian period these basins were not directly connected to each other being separated by wide carbonate platforms and show different evolutionary trends stratigraphic studies in these successions place the triassic jurassic boundary in 6 8 m thick intervals with anoxic facies in the three basins relevant facies changes are also recorded in the late norian in the northern apennines the sedimentation of sulphate evaporites ended being replaced by the rhaetavicula contorta facies whilst in the southern apennines lagonegro basin the deposition of radiolarites began the end of evaporite accumulation can be explained by a climate change from arid to humid conditions and it is also probably linked to an extensional phase preceding the jurassic rifting of the alpine ocean and may therefore have a regional significance nevertheless it corresponds to the spread of the r contorta facies into other parts of southern europe from france to germany and austria the beginning of radiolaritic sedimentation in the lagonegro basin could be related to the rise of atmospheric co2 content linked to volcanic activity in the ionian ridge these facies changes reflect changes of environmental conditions that caused the decline of some fossil associations favoring the development of opportunistic forms e g triasina hantkeni the end triassic extinction coupled with an anoxic episode in all the examined basins immediately preceded a new environmental change documented by the recovery of the carbonate platforms with oolitic facies and different associations the evolution of all these basins suggests that geodynamics were probably responsible for regional events and that at certain moments development reflected global effects as a response to new connections between formerly different domains the central atlantic magmatic province camp volcanism considered as one of the possible causes for the end triassic mass extinction would have had even greater importance if coupled with the volcanism linked to the rifting of the ionian tethys

damage to hdpe geomembrane from interface shear with gravel drainage layer and protection layer abstractmultiinterface direct shear tests have indicated that under high normal stress conditions a hdpe geomembrane can be damaged from interface shear against an overlying gravel drainage layer with or without a protection nonwoven geotextile in between a brief overview of the experimental results is presented and recommendations are provided for mitigation of such damage in field applications

biogeochemical constraints on the triassic jurassic boundary carbon cycle event 1 the end triassic mass extinctions represent one of the five most severe biotic crises in earth history yet remain one of the most enigmatic ongoing debate concerns the environmental effects of the central atlantic magmatic province camp eruptions and their linkage with the mass extinction event across the triassic jurassic boundary there is conflicting paleo evidence for changes in atmospheric pco2 during the extrusion of the camp basalts studies on sediments from european and pacific localities have however identified a substantial negative isotopic anomaly up to 3 5 across the tr j boundary providing an important indicator of changes in the operation of the ancient global carbon cycle we sought to explain the paleo evidence by utilizing a carbon cycle model for the hothouse world of the end triassic that emphasizes the chemical weathering of silicate and carbonate rocks and the ocean carbonate chemistry we find that volcanic co2 outgassing fails to fully account for either a sufficient rise in atmospheric pco2 indicated by the stomata of fossil leaves or the sedimentary isotopic fingerprint instead the scenario that best fits all of the geologic evidence is a positive feedback loop in which warming due to a buildup of volcanically derived co2 triggers destabilization of seafloor methane hydrates and the catastrophic release of ch4 palfy et al 2001 we calculate that this carbon cycle perturbation was huge involving the release of 8000 9000 gt c as co2 during the camp basaltic eruptions and 5000 gt c as ch4 in the model the initial isotopic excursion is assumed to take place over 70 kyr while complete reequilibration of the ocean atmosphere system with respect to co2 is accomplished over 700 1000 kyr our results thus provide a preliminary theoretical explanation for the bioevents estimated pco2 changes and isotopic excursions observed in marine and continental sediments at this time

regional test of a model for shallow landsliding landslides mapped in 14 watershed analyses in oregon and washington provide a regional test of a model for shallow landsliding a total of 3224 landslides were mapped in watersheds covering 2993 km2 and underlain by a variety of lithologies including tertiary sedimentary rocks of the coast ranges volcanic rocks of the cascade range and quaternary glacial sediments in the puget lowlands gis geographical information system techniques were used to register each mapped landslide to critical rainfall values predicted from a theoretical model for the topographic control on shallow landsliding using 30 m dems digital elevation models a single set of parameter values appropriate for simulating slide hazards after forest clearing was used for all watersheds to assess the regional influence of topographic controls on shallow landsliding model performance varied widely between watersheds with the best performance generally in steep watersheds underlain by shallow bedrock and the worst performance in generally low gradient watersheds underlain by thick glacial deposits landslide frequency slides km2 varied between physiographic provinces but yielded consistent patterns of higher slide frequency in areas with lower critical rainfall values simulations with variable effective cohesion predicted that high root strength effectively limits shallow landsliding to topographic hollows with deep soils and locations that experience excess pore pressures but that low root strength leads to higher probabilities of failure across a greater proportion of the landscape 1998 john wiley sons ltd language en

a physically based model for the topographic control on shallow landsliding a model for the topographic influence on shallow landslide initiation is developed by coupling digital terrain data with near surface through flow and slope stability models the hydrologic model topog o loughlin 1986 predicts the degree of soil saturation in response to a steady state rainfall for topographic elements defined by the intersection of contours and flow tube boundaries the slope stability component uses this relative soil saturation to analyze the stability of each topographic element for the case of cohesionless soils of spatially constant thickness and saturated conductivity the steady state rainfall predicted to cause instability in each topographic element provides a measure of the relative potential for shallow landsliding the spatial distribution of critical rainfall values is compared with landslide locations mapped from aerial photographs and in the field for three study basins where high resolution digital elevation data are available tennessee valley in marin county california mettman ridge in the oregon coast range and split creek on the olympic peninsula washington model predictions in each of these areas are consistent with spatial patterns of observed landslide scars although hydrologic complexities not accounted for in the model e g spatial variability of soil properties and bedrock flow control specific sites and timing of debris flow initiation within areas of similar topographic control

late triassic to early jurassic palaeogeography and eustatic history in the nw tethyan realm new insights from sedimentary and organic facies of the csővar basin hungary abstract sedimentary and organic facies of a continuous late triassic early jurassic toe of slope to basin succession of the ne transdanubian range n hungary was studied in order to reconstruct the palaeogeographical and eustatic evolution of the cs var basin an intraplatform basin of the nw neotethys margin characteristic facies successions point to sea level changes of different hierarchies cyclic patterns inferred to result from orbital eccentricity forcing are also reflected in the stratigraphical distribution of sedimentary organic matter furthermore both palaeontological and isotope data document drastic climatic changes around the triassic jurassic boundary detecting sea level changes leads to a more accurate interpretation of the late triassic palaeogeographic setting and evolution of the transdanubian range s carbonate platform our integrated sedimentological and palynological data suggest a complex topography and dynamic sea level history which contradicts a previous model of broad uniform platform setting and lack of any major drowning and emersion events during the late triassic

fire history and the global charcoal database a new tool for hypothesis testing and data exploration version 1 of the global charcoal database is now available for regional fire history reconstructions data exploration hypothesis testing and evaluation of coupled climate vegetation fire model simulations the charcoal database contains over 400 radiocarbon dated records that document changes in charcoal abundance during the late quaternary the aim of this public database is to stimulate cross disciplinary research in fire sciences targeted at an increased understanding of the controls and impacts of natural and anthropogenic fire regimes on centennial to orbital timescales we describe here the data standardization techniques for comparing multiple types of sedimentary charcoal records version 1 of the global charcoal database has been used to characterize global and regional patterns in fire activity since the last glacial maximum recent studies using the charcoal database have explored the relation between climate and fire during periods of rapid climate change including evidence of fire activity during the younger dryas chronozone and during the past two millennia

triassic jurassic organic carbon isotope stratigraphy of key sections in the western tethys realm austria the late triassic period is recognized as one of the five major mass extinctions in the fossil record all these important intervals in earth history are associated with excursions in c isotope records thought to have been caused by perturbations in the global carbon cycle the nature and causes of c isotopic events across the triassic jurassic t j transition however are poorly understood we present several new high resolution organic c isotope records from the eiberg basin austria including the proposed global boundary stratotype section and point gssp for the base of the jurassic the triassic jurassic boundary interval in these records is characterized by the initial and main negative organic carbon isotope excursions cie of up to 8 the initial and main cies are biostratigraphically constrained by first and last occurrences of boundary defining macro and microfossils e g ammonites high resolution c isotope records appear to be an excellent correlation proxy for this period in the eiberg basin pyrolysis analysis demonstrates increased hydrogen index hi values for organic matter coinciding with the initial cie terrestrial organic matter influx and mass occurrences of green algae remains may have influenced the c isotope composition of the sedimentary organic matter this may have contributed to the extreme amplitude of the initial cie in the eiberg basin

stratigraphy and palaeoenvironmental analysis of the triassic jurassic transition in the western southern alps northern italy abstract high resolution stratigraphic studies were carried out on the rhaetian hettangian succession of the bergamasc alps western southern alps italy in order to characterise the stratigraphic and palaeoenvironmental evolution of the lombardian succession across the triassic jurassic t j boundary the t j boundary in the bergamasc alps is sandwiched between the rhaetian carbonate ramp succession of the zu limestone formation and the malanotte formation a new lithostratigraphic unit introduced in this paper deposited during relative sea level rise in the earliest hettangian the zu limestone is organised into subtidal mixed shale carbonate asymmetric cycles documenting the regional evolution from a distal to a proximal depositional environment of an articulated homoclinal carbonate ramp the malanotte formation lacks cyclicity and shows thin bedding and a dominant micritic facies documenting the subtidal evolution of a relatively homogenous outer carbonate ramp environment the microfloral associations record a gradual evolutionary change at the t j boundary whereas the biocalcifying communities appear to be severely affected by the end triassic biotic crisis

carbon isotope anomaly and other geochemical changes at the triassic jurassic boundary from a marine section in hungary most mass extinctions are linked with carbon isotope excursions implying that biotic crises are coupled with changes in the global carbon cycle the isotopic evolution during the end triassic extinction is far less documented than that for the other major phanerozoic extinctions here we report a sharp and short lived 23 5 excursion in carbon isotope values for carbonate d 13 ccarb corresponding to a 22 excursion in the isotopic composition of marine organic matter d 13 corg and other geochemical

triassic environments climates and reptile evolution abstract a consideration of all the available data on triassic vertebrate faunas and their stratigraphic location reveals a relatively sudden extinction event among the last of the mammal like reptiles and the herbivorous rhynchosaurs in the norian of the upper triassic this event was apparently quickly followed by the radiation of the dinosaurs also in the norian this conclusion suggests that competition was not the main factor in the initial success of the dinosaurs but opportunistic radiation following the extinction of major reptile groups a global review of triassic sedimentary facies shows that there were climatic and floral changes towards the end of the triassic it is envisaged that increasing aridity in the later triassic resulting from plate motions and particularly affecting gondwanaland and southwestern laurasia brought about floral changes and then the reptile extinctions with the rapid evolution of new floras of conifers and bennettitaleans the dinosaurs came to dominate all terrestrial faunas within the space of only a few million years

an extended organic carbon isotope record across the triassic jurassic boundary in the queen charlotte islands british columbia canada abstract new lithologic and organic carbon isotope data are presented for the triassic jurassic boundary section at kennecott point queen charlotte islands british columbia canada the previously reported late norian to earliest hettangian record is extended by over 130 m and three new isotopic features are revealed the record now shows a negative offset in baseline carbon isotope values from approximately 29 in the late norian to 31 in the hettangian this offset is accompanied by the previously reported 2 negative excursion at the triassic jurassic boundary and a 5 positive excursion in the early hettangian there is a significant long term negative isotopic trend in the hettangian interval of the section which may be due to camp volcanism the positive excursion is attributed to a decline in bio calcification as well as changes in microbial ecology both related to the mass extinction at the triassic jurassic boundary

foraminiferal biostratigraphy and sequence stratigraphy of peritidal carbonates at the triassic jurassic boundary karaburun peninsula western turkey abstract continuous shallow marine carbonates spanning the triassic jurassic boundary are exposed in the karaburun peninsula western turkey the studied section tahtaiskele section consists of upper triassic cyclic shallow marine carbonates intercalated with clastics overlain by lower liassic carbonates based on the microfacies stacking patterns three main types of shallowing upward cycles have been recognized cycles are mostly composed of subtidal facies at the bottom intertidal supratidal facies and or subaerial exposure structures at the top the duration of the cycles suggests that cycles were driven by the precessional milankovitch rhytmicity in the sequence stratigraphic frame of the tahtaiskele section 4 sequence boundaries were detected and globally correlated the first sequence boundary is located at the alaunian sevatian boundary nearly coinciding with the first appearance of triasina hantkeni the second falls in the rhaetian corresponding to a major sea level fall which led to the invasion of forced regressive siliciclastic deposits over the peritidal carbonates the third occurs close to the t j boundary and the fourth lies slightly above the base of the jurassic in the studied section extinction survival and recovery intervals have been recognized based on the stratigraphic occurrence patterns of benthic foraminifera and algae foraminifers became nearly totally extinct in the inner carbonate shelves at the triassic jurassic boundary and an interval of approximately 0 5 my passed before the begining of the recovery of jurassic foraminifera

service life of a high density polyethylene geomembrane under simulated landfill conditions at 85 c abstractthe time to rupture of a 1 5 mm thick high density polyethylene geomembrane aged in a typical landfill composite liner configuration is investigated under a pressure of 250 kpa at 85 c the geomembrane was underlain with a geosynthetic clay liner and had a 560 g m2 needle pinched nonwoven geotextile protection layer separating it from 50 mm of drainage gravel containing leachate seventeen 0 6 m diameter tests were conducted in addition to 9 months required to deplete antioxidants stage i the tests indicated a lag period stage ii of 5 5 months and a time from the start of degradation to rupture stage iii of 20 months giving a total inferred time to rupture of 34 5 months 2 9 years there were up to 61 brittle ruptures per sample i e 2 million cracks per hectare the ruptures were predominately oriented in the machine direction and located 1 directly beneath a gravel contact 2 at the side of a gravel indentation or 3 between gravel indentations the ruptures between gravel

interface shear damage to a hdpe geomembrane ii gravel drainage layer abstractan experimental program of large scale direct shear tests has indicated that shear displacement of a gravel drainage layer and nonwoven geotextile protection layer over a high density polyethylene hdpe geomembrane under moderate to high normal stress conditions can cause much greater damage to the geomembrane than static pressure alone essentially no damage was observed at low normal stress the greatest damage occurred at high normal stress 1 389 kpa using a lightweight geotextile 335 g m2 and yielded an average of 31 holes m2 with a maximum hole size of 29 mm surprisingly geomembrane damage measured using a lightweight geotextile was greater than that measured using no geotextile due to a change in failure surface location for the same conditions shear induced damage was slightly less for a geomembrane placed on a compacted sand subgrade than on a compacted clay subgrade interface shear strength increased significantly with decreasing geotextile mass area due to greater out of plan

frequency and spatial distribution of landslides in a mountainous drainage basin western foothills taiwan maps from 1904 and 1915 and air photographs from 1963 1980 1985 1993 and 1996 provide a record of landslide incidence in a 92 1 km2 drainage basin a headwater tributary of the cho shui river in taiwan interpretation of landslide patterns from the early maps indicate that in four sub basins 36 km2 structural geological factors control chronic landsliding regularly reactivated by intense rains within these four sub basins all later air photographs reveal a continuing high incidence of landslides with landslide densities of 3 11 ha km2 air photographs taken in 1963 following extensive logging in 1985 following highway construction and in 1996 following the very large typhoon herb event demonstrate the short term effects of disturbance in these structurally weak sub basins air photographs from 1980 and 1993 demonstrate recovery of the land surface from logging and highway construction impacts respectively for the adjacent sub basins 56 km2 two modes of response to perturbations were identified six sub basins 48 km2 showed direct response to logging road construction and typhoon herb and five sub basins 8 km2 were more buffered and showed some lagged responses even this last category of sub basins is more active than the average for taiwan where the mean landslide density is 0 84 ha km2 it is proposed that for the 92 1 km2 hoshe basin the formative event sensu brunsden z geomorphol suppl 79 1990 1 is one that produces approximately 200 ha of landslides a value that has been equaled or exceeded in each of the periods of study 1963 1980 1980 1985 1985 1993 and 1993 1996 logging activity major road construction and extreme typhoon and earthquake events produce short term acceleration of landslide incidence in principle recovery rates of the land from pulsed perturbations of about 20 years for logging activity and about 8 years for major road construction may also be suggested

carbon isotope stratigraphy and palynostratigraphy of the triassic jurassic transition in the tiefengraben section northern calcareous alps austria abstract the end triassic is characterized by enhanced rates of biotic turnover in both the marine and terrestrial realms carbon isotope anomalies have been reported worldwide that may indicate coeval global disturbances in the biogeochemical cycles here we present the results of an integrated study of the palynomorph assemblages and the carbon isotope composition of organic matter in the tiefengraben section near st wolfgang austria carbon isotope values from bulk organic matter show significant fluctuations through the triassic jurassic t j boundary interval with two prominent negative 13 c org excursions an initial negative carbon isotope excursion occurs at the base of the kendlbach formation tiefengraben member pre planorbis beds although triassic ammonoids and conodonts have their highest occurrence at the top of the underlying kossen formation the palynomorph and calcareous microfossil assemblages indicate still a rhaetian age for the lower part of the tiefengraben member high abundance of prasinophytes during the interval of the initial carbon isotope excursion may represent a bloom of green algae that flourished as a result of the disturbance of the marine ecosystems increased spore abundance together with the disappearance of distinctive late triassic pollen types e g ovalipollis rhaetipollis indicate vegetation changes on land that are contemporaneous with the marine biotic crisis a second negative carbon isotope excursion occurs in the middle part of the tiefengraben member based on palynological evidence the t j boundary may be drawn at about this level by the lowest occurrence of cerebropollenites thiergartii the established carbon isotope curve as well as palynostratigraphic and other biostratigraphic events can be correlated with st audrie s bay england

the potential contribution of geomorphology to tropical mountain development the case of the manrecur project abstract a comprehensive interdisciplinary study of a small andean watershed in ecuador poats j v 2002 el angel river watershed carchi ecuador disk 9 of 9 in himalayan andean collaborative watershed project international development resource centre ottawa has produced practical recommendations for its sustainable management with emphasis on new governance mechanisms comparatively little is said about questions of watershed stability in geomorphic terms though water supply sources and sinks are identified as crucially important in this paper three alternative frameworks those of montology less favoured area investment and panarchy are examined it is concluded that each of these frameworks by insisting on a balance between socio economic and biophysical analysis does offer scope for the incorporation of geomorphic concepts though none of them demand explicit geomorphic content the framework which seems most flexible is the panarchy metaphor holling c s 2001 understanding the complexity of economic ecological and social systems ecosystems 4 390 405 not only does this framework insist on asking questions about the socio economic and biophysical organisation of the watershed system but it also leads to some arresting conclusions about the probable imminent collapse of watersheds under increasing population and land use pressure the panarchy metaphor identifies collapse and reorganisation as a common characteristic of socio economic and biophysical systems if this metaphor is even close to being accurate the first issue in sustainable management of this small andean watershed is how to ensure a creative collapse leading to a more sustainable system a significant geomorphic contribution in this context would seem to include the identification of functioning hydro geomorphic response units connectivities and spatial scale effects leading to more nuanced application of management strategies

disequilibrium of holocene sediment yield in glaciated british columbia it is generally supposed that specific sediment yield the quantity of sediment passing a monitored river cross section per unit area drained upstream of that section declines as the area drained increases1 3 part of the sediment mobilized from the land surface is supposed to go back into storage at field edges and on footslopes and floodplains in contrast we show here that data from british columbian rivers reveal a pattern of increasing specific sediment yield at all spatial scales up to 3 104 km2 this results from the dominance of secondary remobilization of quaternary sediments along river valleys over primary denudation of the land surface the result controverts the conventional model which has been derived from studies of small highly disturbed agricultural catch ments the rivers are still responding to the last glaciation giving a landscape relaxation time greater than 10 kyr this holds pro found implications for geomorphological theory and for studies of erosion