petrographic and geochemical analysis of caliche profiles in a bahamian pleistocene dune two caliche profiles from a pleistocene carbonate dune on san salvador island bahamas were examined by petrographic and geochemical analysis profile a is an immature buried caliche profile characterized by caliche pisolites a friable crust and abundant cerion profile b is a more well developed caliche profile at the top of the dune which contains abundant pisolites rhizomorphs laminated calcrete a breccia and abundant cerion geochemical changes in caliche profiles relative to the host rock are an increase in al2o3 fe2o3 and total organic carbon a decrease in mg and sr and a decrease in 13ccarb 18ocarb and 13corg the magnitude of these changes is probably a function of the duration of subaerial exposure and resultant colonization by dune plants and associated microflora abundance of calcified filaments and needle fibre crystals in profile a attests to the importance of microbial processes in the early development of caliche profiles biogenic structures are largely destroyed in profile b due to recrystallization but indirect evidence of biological activity is retained in the form of carbon isotope values

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

failure of volcano slopes magmatic intrusions can initiate and sustain massive and catastrophic volcano collapse their role is twofold involving both driving and resisting forces first flank stability is diminished by magmastatic and magma overpressures and steepened slopes that accompany intrusion second excess pore pressures in potential failure zones can be generated as a result of intrusion related mechanical or thermal straining of the rock fluid medium pressurized retrograde boiling in high level magma chambers or hydrothermal fluid circulation also earthquakes may aid collapse through inertial forces and shaking induced pore pressure generation these excess pore pressures reduce the sliding resistance as shown for wedge shaped slide blocks for selected cases the destabilizing influence of mechanically induced pore pressures is maximized as the intruded width or corresponding overpressure of the intrusion is increased the destabilizing influence of thermally induced pore pressures is conditioned by the seve

recent dyke induced large scale block movement at mount etna and potential slope failure here we report the results of a geodetic survey undertaken on mount etna between 1981 and 1988 observed horizontal ground movements in the vicinity of the valle del bove caldera demonstrate that dyke emplacement during 1983 and 1985 resulted in the 2 8 m eastward displacement of a block of western caldera rim a history of past instability and collapse along the rim is indicated by the presence of large back rotated blocks of prehistoric volcanics1 furthermore the unusually linear form of the present western rim indicates past slope failure along north south aligned surfaces and therefore that dyke induced collapse may have been an important agent in caldera enlargement we suggest a self sustaining mechanism whereby the stress regime generated as a consequence of the caldera s existence results in the repeated injection of north south orientated dykes adjacent to the western rim2 3 dilation associated with magma intrusion leads in turn to periodic phases of slope instability and failure of the cliff wall causing a progressive westward migration of the western rim

late pleistocene landscape response to climate change eolian and alluvial fan deposition cape liptrap southeastern australia abstract sea cliffs along the western coast of cape liptrap at arch rock provide nearly continuous exposure of calcareous eolianites dated at 68 112 ka five optically stimulated luminescence osl ages calcareous eolian deposition began immediately after the last interglacial marine highstand oxygen isotope stage ois 5e and continued during sea level fall until the beginning of ois 4 west southwesterly winds transported calcareous sand across 12 km of exposed continental shelf by the beginning of ois 4 a brief period of cold arid windy continental climate with ephemeral but intense surface runoff immediately preceded the last glacial maximum lgm this resulted in fluvial reworking of the calcarenites into an alluvial fan dated at 23 25 ka four osl ages the fan overlies peat dated at 25 279 yr cal bp and is capped by a paleosol dated at 6010 yr cal bp concurrent eolian reworking by northwesterly winds of siliceous sediments on marine terraces along the eastern and central portion of cape liptrap formed siliceous longitudinal dunes with ages ranging from 19 to 24 ka five osl ages the phase of maximum landscape instability at cape liptrap coincides with solar insolation and air temperature minima and preceded the lgm by several thousand years

very shallow earthquakes and brittle deformation in active volcanic areas the eatnean region as an example abstract some aspects of the stress field acting in active volcanic areas were investigated by studying the relationship between surficial seismicity h 1 2 km and the brittle deformation pattern of the etna volcano the magmatic composition and structural character of mt etna are described together with its geodynamic regional context after a discussion of the problem of the state of stress in active volcanoes and a definition of very shallow seismicity the high level of surficial seismicity the morphology of the sedimentary basement and the kinematic behaviour of the faults suggest that the eastern flank of mt etna is a shallow seismotectonic domain structurally decoupled from the rest of the volcanic body this flank shows a tendency to slide in an eastern direction and is bound to the north by a left lateral oblique slip normal fault trending e w and in the south by an arcuate fault system with right lateral features right lateral oblique slip normal faults

evolution of ocean island rifts the northeast rift zone of tenerife canary islands the northeast rift zone of tenerife presents a superb opportunity to study the entire cycle of activity of an oceanic rift zone field geology isotopic dating and magnetic stratigraphy provide a reliable temporal and spatial framework for the evolution of the ne rift zone which includes a period of very fast growth toward instability between ca 1 1 and 0 83 ma followed by three successive large landslides the micheque and guimar collapses which occurred approximately contemporaneously at ca 830 ka and on either side of the rift and the la orotava landslide between 690 10 and 566 13 ka our observations suggest that canarian rift zones show similar patterns of development which often includes overgrowth instability and lateral collapses collapses of the rift flanks disrupt established fissural feeding systems favoring magma ascent and shallow emplacement which in turn leads to magma differentiation and intermediate to felsic nested eruptions rifts and their collapses may therefore act as an important factor in providing architectural and petrological variability to oceanic volcanoes conversely the presence of substantial felsic volcanism in rift settings may indicate the presence of earlier landslide scars even if concealed by postcollapse volcanism comparative analysis of the main rifts in the canary islands outlines this general evolutionary pattern 1 growth of an increasingly high and steep ridge by concentrated basaltic fissure eruptions 2 flank collapse and catastrophic disruption of the established feeder system of the rift 3 postcollapse centralized nested volcanism commonly evolving from initially ultramafic mafic to terminal felsic compositions trachytes phonolites and 4 progressive decline of nested eruptive activity

characterization of debris avalanche deposits in japan abstract seventy one debris avalanche deposits are identified from 52 japanese quaternary volcanoes the structures of these volcanoes are mostly stratovolcanoes and lava domes no avalanche deposit is found in calderas pyroclastic cones or maar volcanoes debris avalanche deposits are found in 18 of all quaternary volcanoes or 25 of quaternary stratovolcanoes and lava domes the ratio rises to 49 when considering only active stratovolcanoes and lava domes at least five debris avalanche deposits have formed since 9th century the maximum height difference of sliding h for each debris avalanche ranges from 200 to 2400 meters and the maximum runout distance of sliding l ranges from 1 6 to 32 km the ratio h l ranges from 0 2 to 0 06 and becomes smaller in larger debris avalanches they are more mobile than landslides in non volcanic areas volume is within a range of 0 03 and 9 km 3 there is no relation between the direction of sliding and the regional horizontal compressional stress axis at the site of a volcano two dimensional computer simulations of avalanches using a simplified physical model are made the maximum velocity is mainly controlled by the length of steep slope

calcrete in quaternary coastal dunes in southwestern australia a capillary rise phenomenon associated with plants abstract non pedogenic calcrete is forming as a thin sheet 10 50 cm thick just above the water table in the subsurface of a barrier dune terrain in south western australia the calcrete is forming in response to the regional evapo transpirative regime the annual rainfall is high but of short duration and it infiltrates rapidly into the sandy substrates relatively high air temperatures and evaporation coupled with wind stress combine to produce a water vapor deficit across the dune terrain the vegetation responds by drawing upon phreatic water and pellicular water of the vadose zone thereby precipitating caco3 where plants are not drawing phreatic water calcrete is developing by evaporation of water at the top of the zone of capillary rise various structure types of calcrete are developed in the study area namely rhizoconcretionary mottled massive and laminar forms these occur in a definite stratigraphic sequence related to maturity of profile vegetation cover and thickness of the vadose zone rhizoconcretionary calcrete forms in the vadose zone mottled and massive calcrete frequently capped by laminar calcrete develop in the zone of capillary rise these latter calcrete types form a sheet that is ubiquitous and parallel to the water table since it is a feature of the water table the calcrete sheet may potentially transect regional stratigraphic boundaries and unconformities at the local level the various structural types of calcrete may he used as paleowater table indicators

aeolianite calcrete microbialite and karst in southwestern australia as indicators of middle to late quaternary palaeoclimates abstract the mid late pleistocene and holocene aeolianites of the tamala limestone on the northern swan coastal plain in southwestern western australia consist of six members that show cyclic deposition of coastal aeolianite overlain by calcrete microbialite karstified surface and palaeosol field work combined with mineralogical chemical stable isotope analysis and uranium thorium u th and optically stimulated luminescence osl dating provides an insight into the repetitive glacial and interglacial climatic periods over the past 500 kyr deposition of the carbonate aeolianites occurred during interglacial episodes marine isotope stage mis 1 5 7 9 11 and possibly 13 due to migration of coastal dunes under the influence of strong southerly to southwesterly winds rainfall was insufficient to support vegetation cover on the dunes and so was probably limited or seasonal the transition from interglacial to glacial climates was characterised by higher effective rainfall accompanied by aeolianite dissolution and karstification during the colder climates and less effective rainfall of the glacial periods there was no carbonate sand deposition instead laminated microbialite and or laminar calcrete formed followed by palaeosol formation the oxygen isotope composition of the microbialites indicates average temperatures during glacial periods 4 c 8 c lower than today and 13 c values demonstrate a higher proportion of c4 plants and therefore a drier or more seasonal climate data from individual members of the tamala limestone show that the wettest interglacial period was mis 5 when extensive karstification and pinnacle development occurred and rainfall was probably higher than at any other time in the past 500 kyr of the glacial periods mis 10 was relatively wet or less seasonal whereas mis 8 and the last glacial maximum lgm were relatively dry and windy the low rainfall during the peak of the glacial periods was probably intensified by colder water offshore due to weakening of the leeuwin current and its replacement by the cold north flowing west australian current

causes and mobility of large volcanic landslides application to tenerife canary islands abstract giant volcanic landslides are one of the most hazardous geological processes due to their volume and velocity since the 1980 eruption and associated debris avalanche of mount st helens hundreds of similar events have been recognised worldwide both on continental volcanoes and volcanic oceanic islands however the causes and mobility of these enormous mass movements remain unresolved tenerife exhibits three voluminous subaerial valleys and a wide offshore apron of landslide debris produced by recurrent flank failures with ages ranging from upper pliocene to middle pleistocene we have selected the la orotava landslide for analysis of its causes and mobility using a variety of simple numerical models first the causes of the landslide have been evaluated using limit equilibrium method and 2d finite difference techniques conventional parameters including hydrostatic pore pressure and material strength properties together with three external processes dike intrusion caldera collapse and seismicity have been incorporated into the stability models the results indicate that each of the external mechanism studied is capable of initiating slope failures however we propose that a combination of these processes may be the most probable cause for giant volcanic landslides second we have analysed the runout distance of the landslide using a simple model treating both the subaerial and submarine parts of the sliding path the effect of the friction coefficient drag forces and hydroplaning has been incorporated into the model the results indicate that hydroplaning particularly can significantly increase the mobility of the landslide which may reach runout distances greater than 70 km the models presented are not considered definite and have mainly a conceptual purpose however they provide a physical basis from which to better interpret these complex geologic phenomena and should be taken into account in the prediction of future events and the assessment of landslide related hazards

evidence for obliquity forcing of glacial termination ii variations in the intensity of high latitude northern hemisphere summer insolation driven largely by precession of the equinoxes are widely thought to control the timing of late pleistocene glacial terminations however recently it has been suggested that changes in earth s obliquity may be a more important mechanism we present a new speleothem based north atlantic marine chronology that shows that the penultimate glacial termination termination ii commenced 141 000 2500 years before the present too early to be explained by northern hemisphere summer insolation but consistent with changes in earth s obliquity our record reveals that terminations i and ii are separated by three obliquity cycles and that they started at near identical obliquity phases

vertical and lateral collapses on tenerife canary islands and other volcanic ocean islands recent studies demonstrate that tenerife has undergone large lateral collapses this has led to the suggestion that the las canadas caldera one of the best exposed calderas in the world is the result of lateral collapse we have tested this idea using the available structural stratigraphic volcanological and geochronological data we conclude that the las canadas caldera is the result of a complex sequence of vertical collapse events associated with a long history of phonolitic explosive activity in the central part of tenerife our results indicate however that vertical collapses may have played a major role in triggering lateral collapses we propose that the association of vertical and lateral collapse events such as inferred for tenerife can also explain similar sequences of events interpreted to have affected other large volcanic ocean islands

catastrophic collapse at stratovolcanoes induced by gradual volcano spreading unlike ordinary mountains which are formed by slow uplift and erosion volcanoes are constructed rapidly as a consequence many are liable to massive flank failures leading to debris avalanches for example at mount st helens in 1980 such failures occur worldwide about once every 25 years ref 1 and even small ones can present a major hazard in particular if far reaching tsunamis are generated as at mayu yama in 1792 ref 2 previous work has tended to emphasize differences in eruption style associated with flank failure2 but here we focus on the fundamental structural causes of failure most volcanic failures are generated by magmatic intrusion and flank spreading3 we present evidence however that mombacho volcano in nicaragua experienced a previously unrecognized type of failure triggered by sub volcanic basement spreading notably collapses related to basement spreading do not require that the volcano be magma tically active and thus flank failure may pose a significant risk even at inactive volcanoes which are rarely monitored

geomorphological evidence for a changing tectonic regime pasinler basin turkey the pasinler basin in the east anatolian contractional province features a suite of geomorphological zones visible in the field air photographs and landsat and shuttle radar topography mission srtm digital elevation model imagery these zones reflect past and current tectonically influenced processes relicts of the erzurum kars plateau representing mio pliocene volcanism associated with transtensional tectonics have been modified by two stages of drainage development an earlier shallow valley network which was modified following uplift and tilting to form the present system characterized by deep narrow valleys that supply alluvial fan complexes these fans discharge onto the present aggradation dominated basin floor initial normal faulting induced massive slope failures on the basin9s northern margin this extensional phase within the basin was reversed by the late pleistocene with thrust faults modifying and producing landforms and affecting sediment sequences along both its northern and southern margins the shift from a transtensional regime and the associated volcanism to normal faulting in the pliocene to early pleistocene and then to the present regime of compression induced thrusting appears to correspond to a regional tectonic shift resulting from the collision of the eurasian and arabian plates and the subsequent westwards movement of the anatolian microplate

long term 17 ma turbidite record of the timing and frequency of large flank collapses of the canary islands volcaniclastic turbidites on the madeira abyssal plain provide a record of large volume volcanic island flank collapses from the canary islands this long term record spans 17 ma and comprises 125 volcaniclastic beds determining the timing provenance and volumes of these turbidites provides key information about the occurrence of mass wasting from the canary islands especially the western islands of tenerife la palma and el hierro these turbidite records demonstrate that landslides often coincide with protracted periods of volcanic edifice growth suggesting that loading of the volcanic edifices may be a key preconditioning factor for landslide triggers furthermore the last large volume failures from tenerife coincide with explosive volcanism at the end of eruptive cycles many large volume canary island landslides also occurred during periods of warmer and wetter climates associated with sea level rise and subsequent highstand however these turbidites are not serially dependent and any association with climate or sea level change is not statistically significant

multi event oceanic island landslides new onshore offshore insights from el hierro island canary archipelago abstract this paper presents a combined onshore offshore morpho structural characterization of the el golfo giant landslide island of el hierro canary archipelago spain offshore data from multibeam echosounders chirp sub bottom profiles and multichannel seismic reflection data and onshore data coming from water wells and galleries have been analyzed the geomorphology and the internal architecture of this giant flank collapse are defined in order to determine its multi event nature the subaerial headscarp shows a non continuous arcuate profile formed by two nested semi circular amphitheaters that extend offshore along a smooth chute suggesting the occurrence of at least two large retrogressive events channels gullies and escarpments developed along the submarine sector of the scar also indicate smaller scale events and predominance of sediment bypass in the lower slope two subunits of submarine mass transport deposits mtds debris avalanche are identified on multichannel seismic reflection profiles with a total estimated volume of 318 km3 84 km3 and 234 km3 for the younger and older mtds respectively data from wells and galleries show abrasion platforms with beach deposits at sea level 0 masl formed after the landslide scar and buried by the post collapse el golfo lavas infill suggesting an age at least older than 23 5 82 5 ka for the landslide

the anthropogenic nature of present day low energy rivers in western france and implications for current restoration projects abstract as in other european countries western france has seen an increase in river restoration projects in this paper we examine the restoration goals methods and objectives with respect to the long term trajectory and understanding of the contemporary dynamics of the small low energy rivers typical of the lowlands of western europe the exhaustive geomorphological paleoenvironmental and historical research conducted in the seulles river basin normandy provides very accurate documentation of the nature and place of the different legacies in the fluvial systems we have inherited the sedimentation rate in the seulles valley bottom has multiplied by a factor of 20 since the end of the bronze age and has generated dramatic changes in fluvial forms hydraulic control of the rivers and valley bottoms drainage throughout the last millennium has channelized rivers within these deposits the single meandering channel which characterizes this river today is the legacy of the delayed and complex effects of long term exploitation of the river basin and the fluvial system bring to light that the naturalness of the restored rivers might be questioned our research emphasizes the gap between the poor knowledge of the functioning of these rivers and the concrete objectives of the restoration works undertaken including dam and weir removal account of the long term history of fluvial systems is required not only to produce a pedagogic history of the river degradation but more fundamentally i to situate the current functioning of the fluvial system in a trajectory to try to identify thresholds and anticipate the potential turning points in a context of climate and land use change ii to understand the role of morphosedimentary legacies on the current dynamics iii to open the discussion on reference functioning or expected states and iv to open discussion on the sustainability of ecological restoration to conclude we point out the necessity to take into account the hybrid nature of low energy rivers in rural environments and to develop specific evaluation protocols which would include both biophysical processes and usual human activities which could be a way to share the evaluation and overcome conflicts between socioeconomic needs and environmental issues

volcanic evolution of the island of tenerife canary islands in the light of new k ar data new age determinations from tenerife together with those previously published 93 in all provide a fairly comprehensive picture of the volcanic evolution of the island the oldest volcanic series with ages starting in the late miocene are formed mainly by basalts with some trachytes and phonolites which appear in anaga teno and roque del conde massifs in anaga ne three volcanic cycles occurred one older than 6 5 ma a second one between 6 5 and 4 5 ma with a possible gap between 5 4 and 4 8 ma and a late cycle around 3 6 ma in teno nw after some undated units the activity took place between 6 7 and 4 5 ma with two main series separated by a possible pause between 6 2 and 5 6 ma in the zone of roque del conde s the ages are scattered between 11 6 and 3 5 ma between 3 3 and 1 9 ma the whole island underwent a period of volcanic quiescence and erosion the large canadas volcano made up of basalts trachytes and phonolites was built essentially between 1 9 and 0 2 ma to the ne of this central volcano linking it with anaga is a chain of basaltic emission centers with a peak of activity around 0 8 ma the canadas caldera had several collapse phases associated with large ignimbrite emissions there were at least an older phase more than 1 ma old on the western part of the volcano and a younger one less than 0 6 ma old in the eastern side the two large valleys of guimar and la orotava were formed by large landslides less than 0 8 ma ago and probably before 0 6 ma ago the present canadas caldera was formed by another landslide less than 0 2 ma ago this caldera was later filled by the huge teide volcano which has been active even in historic times during the same period a series of small volcanoes erupted at scattered locations throughout the island the average eruptive rate in tenerife was 0 3 km3 ka with relatively small variations for the different eruptive periods this island and la gomera represent a model of growth by discontinuous pulses of volcanic activity separated by gaps often coinciding with episodes of destruction of the edifices and sometimes extended for several million years the neighbouring gran canaria on the other hand had an initial rapid shield building phase during which more than 90 of the island was built and a series of smaller pulses at a much later period a comparison between these three central islands indicates that the previously postulated westward displacement in time of a gap in the volcanic activity is valid only as a first approximation several gaps are present on each island overlapping in time and not clearly supporting either of the models proposed to explain the evolution of the canaries

large scale mass wasting in ancient volcanic materials abstract giant landslides are significant hazards associated with many active volcanic edifices we describe a similar feature on ancient 4 ma volcanic deposits subject to active tectonism the landslide is approximately 3 km long by 1 km wide with an estimated depth of 400 m side margins are straight and parallel mimicking regional structure narrow valleys incised down these margins provide low strength side release surfaces between these is a giant slump consisting of at least four largely intact discrete blocks that have moved down dip a distance of 500 m a series of flows with areal extents ranging from 0 01 to 0 5 km 2 extends from the front of the failure the materials represent an eroded sequence of andesite flows on the flanks of a stratovolcano these have undergone two phases of hydrothermal alteration and are deeply weathered to low density 1040 80 kg m 3 silt 59 and clay 35 materials with strength properties typical of weathered silts c 26 3 kn m 2 42 8 the size and location of this landslide preclude detailed geotechnical investigation of the failure the worth of numerical stability analysis as an alternative technique in assessing the nature of the failure and hence the risk it poses to nearby communities is investigated sensitivity analysis identified likely conditions under which initial failure may have occurred analyses for sensitivity to strength and earthquake acceleration needed conversion to critical combinations f 1 0 of water table and strength acceleration to remove the overriding influence of water table fluctuations failure was likely initiated either by a high water table level 83 84 or some combination of intensity vii ix earthquake waves together with water table heights of 40 80 a general hazard assessment indicates that the risk associated with creep and catastrophic failure of the main mass is small whereas the risk from flow failures near the toe of the landslide may be high important parameters hydrological regime flow failure morphology age of initiation and rates of movement requiring closer investigation are identified development of a model is crucial to assessing the hazard associated with a feature such as that described here with limited resources a detailed stability analysis is a powerful tool as an initial stage in hazard analysis

role of olivine cumulates in destabilizing the flanks of hawaiian volcanoes the south flank of kilauea volcano is unstable and has the structure of a huge landslide it is one of at least 17 enormous catastrophic landslides shed from the hawaiian islands mechanisms previously proposed for movement of the south flank invoke slip of the volcanic pile over seafloor sediments slip on a low friction decollement alone cannot explain why the thickest and widest sector of the flank moves more rapidly than the rest or why this section contains a 300 km3 aseismic volume above the seismically defined decollement it is proposed that this aseismic volume adjacent to the caldera in the direction of flank slip consists of olivine cumulates that creep outward pushing the south flank seawards average primary kilauea tholeiitic magma contains about 16 5 wt mgo compared with an average 10 wt mgo for erupted subaerial and submarine basalts this difference requires fractionation of 17 wt 14 vol olivine phenocrysts that accumulate near the base of the magma reservoir where they form cumulates submarine erupted kilauea lavas contain abundant deformed olivine xenocrysts derived from these cumulates deformed dunite formed during the tholeiitic shield stage is also erupted as xenoliths in subsequent alkalic lavas the deformation structures in olivine xenocrysts suggest that the cumulus olivine was densely packed probably with as little as 5 10 vol intercumulus liquid before entrainment of the xenocrysts the olivine cumulates were at magmatic temperatures 1100 c when the xenocrysts were entrained olivine at 1100 c has a rheology similar to ice and the olivine cumulates should flow down and away from the summit of the volcano flow of the olivine cumulates places constant pressure on the unbuttressed seaward flank leading to an extensional region that localizes deep intrusions behind the flank these intrusions add to the seaward push this mechanism ties the source of gravitational instability to the caldera complex and deep rift systems and therefore limits catastrophic sector failure of hawaiian volcanoes to their active growth phase when the core of olivine cumulates is still hot enough to flow

extensive perched aquifer and structural implications revealed by 3d resistivity mapping in a galapagos volcano abstract due to the complexity of geological formations and limited subsurface data in volcanic islands hydrogeological conceptual models can differ from one island to another and for the same island the galapagos islands like most inhabited volcanic islands face important water resource problems which might have a major impact on their unique and pristine ecosystems endanger world heritage list june 2007 the scarcity of geological and hydrological data combined with the difficulty of access for field measurements lead to a poor understanding of the island hydrogeology and unconvincing interpretation of traditional geophysical data here we present three dimensional 3 d resistivity maps for the supposedly waterless santa cruz island obtained by using the skytem device a helicopter borne transient electromagnetic method the latter is non invasive and measurements over inaccessible terrain were of vital importance we show that even in high relief terrain with extreme subsurface resistivity contrasts 1 6 000 ohm m the method is sensitive to low resistivity layers of hydrogeological interest 50 200 ohm m to a depth of approximately 300 m the unique spatial resolution and 3 d view of the subsurface resistivity structures allow identification of two zones of hydrogeological importance a previously unknown extensive perched aquifer 50 km 2 on the southern mountain side and the geometry of the salt water wedge in the basal aquifer located with an accuracy of a few meters this finding supports the existence of hidden perched aquifers on basaltic islands until now only inferred from hydrogeological studies it is seen to be affected by faulting beyond the vital implications for water resource and ecosystem management in the unique yet severely threatened galapagos islands some conceptual flow models of volcanic islands have to be reconsidered the presence of such structures in a volcanic edifice recognized as low strength layer may help to explain the origin of potentially catastrophic landslides

present day downcutting of the raba river channel western carpathians poland and its environmental effects abstract timing and causes of the present day channel downcutting of carpathian tributaries to the vistula river are exemplified by a case study of the raba river a gravel bed stream characterized by great variability of water stage and discharge up to 3 m of river incision has occurred since the beginning of the present century associated with an increase in stream power caused by river control works and reduction in bed material load linked to changes in basin management gravel extraction from the channel and modifications in flood flows have increased rates of incision over the last thirty years lowering of ground water levels on the valley floor increase in river bank susceptibility to erosion decrease or cessation of overbank sediment accretion and impoverishment of plant and animal communities of riverside biotopes are the principal environmental effects of channel downcutting

mechanical relationship between catastrophic volcanic landslides and caldera collapses large scale sector collapses of volcanic edifices and collapse calderas represent some of the most catastrophic geological events taking place at the earth s surface examples of these two processes occurring simultaneously suggest that a mechanical relationship between landslides and collapse calderas may exist we demonstrate that a caldera collapse can trigger large scale landslides in volcanic terrains moderate seismic shocks caused by seismogenic slip on the ring fault on which the caldera subsidence takes place act as the driving force necessary to destabilize the volcano flank this process is favored on steep volcanoes and where flank strength is reduced by agents such as hydrothermal alteration pore fluid pressure increase or the presence of weak soils

spatial disaggregation and aggregation procedures for characterizing fluvial features at the network scale application to the rhone basin france network scale heterogeneity in fluvial forms and processes has been analyzed for decades through the field based characterization of a reduced number of sites spatially continuous data sets are increasingly available at a national scale e g digital elevation models or aerial orthophotographs and open up new possibilities to investigate spatial structures in stream networks the paper introduces a gis methodological framework to support and automate the large scale characterization of the fluvial system based on spatial disaggregation and aggregation procedures the spatial disaggregation consists in the longitudinal discretisation of geographical objects into relatively high resolution spatial units to characterize fluvial features continuously along stream networks because rivers are heterogeneous and hierarchically organized the spatial aggregation aims to delineate statistically pattern or process based spatial units to answer questions at appropriate scales the paper develops the gis implementation of the disaggregation and aggregation procedures for characterizing stream networks in a geomorphic perspective we illustrate the approach on the rhone network focusing on the characterization of three geographical objects commonly used in classification schemes the streamline the valley bottom and the active channel the latter on a limited area the spatial aggregation is automated using the threshold test of pettitt 1979 to detect change points in univariate data series and delineate homogeneous spatial units throughout the stream network we provide three simple application examples to illustrate the potentialities of the spatial aggregation to investigate spatial heterogeneity in stream networks finally insights limitations and future challenging issues emerging from the application of the methodological framework are discussed

large ferruginized palaeorhizospheres from a paleogene lateritic profile of uruguay abstract it is proposed herein that columns included in the unconformity between mercedes upper cretaceous and asencio lower eocene formations of uruguay forming caves known since the xix century are large ferruginized palaeorhizospheres diagnostic characters are concentric internal structure radiating secondary prolongations preservation of original lamination trace fossils and other attributes of the original deposit in contrast with rhizoliths which originated as root casts or by roots and their peritrophic zones palaeorhizospheres are originated from peritrophic zones to a few tens of centimeters in the soil surrounding the roots in many cases like those presented herein rhizoliths are not preserved inside the palaeorhizospheres specimens were studied in 6 localities from central uruguay where 5 different morphological types were recognized according to its internal structure 1 rimmed 2 concentric 3 concentric disrupted 4 nodular or mottled and 5 brecciated the palaeorhizosphere hypothesis can explain this diversity of internal structures which may be compatible with different stages of root and rhizosphere development types 1 and 2 could be produced by living roots whereas 3 to 5 more probably by percolation and staining by fe solutions coming from the overlying asencio formation through decaying or dead roots the rim that surrounds most structures may be interpreted as the boundary of the original rhizosphere where fe ions translocated outward from the root by chelation found oxidizing conditions concentric pattern would result from the centrifugal displacement of the oxidizing rim type 3 to 5 structures would start when most biologic processes around the living or decaying root cease and periodic formation of rings stops even when palaeorhizospheres are included in the mercedes formation their possibility to be produced during mercedes times is unlikely because the strong oxidation processes involved were exclusive of the asencio times when favored by the early eocene climate optimum laterites reached the latitude of uruguay large palaeorhizospheres are probably common features in many continental successions but mostly overlooked or misinterpreted until now

assessment of downstream trends in channel gradient total and specific stream power a gis approach geographic information systems gis analyses of digital elevation models dems coupled with catchment area based discharge estimation techniques provide a relatively simple means of modelling contiguous downstream trends in channel gradient total stream power and in riverscapes conducive to regime analysis also specific stream power for a small high relief coastal catchment in se australia good agreement was obtained between channel gradients derived from a 25 m cell size dem and field survey equivalents over distances of several kilometres indicating that channel gradients derived from dems can have a reasonable degree of absolute as well as relative accuracy over multi kilometre reach scales assessment of downstream rates of change in channel gradient and specific stream power across four river systems suggests that some of the river reaches most responsive to high magnitude floods occur in zones where these variables rapidly decrease downstream modelling of downstream trends in channel gradient total and specific stream power from catchment wide dems has potential to provide a framework with which to investigate conceptual and empirical models between channel gradient stream power and the form and dynamics of river systems

morphological and geological aspects related to large slope failures on oceanic islands the huge la orotava landslides on tenerife canary islands huge volcanic landslides are one of the most hazardous geomorphological processes that can occur during the evolution of volcanic ocean islands the causes of these phenomena however are very complex and combine non volcanic and volcanic factors in the canary islands more than 20 events have been detected during the last decades a detailed analysis was carried out for la orotava amphitheatre on tenerife in order to understand the relationship between geomorphological and geological aspects and huge volcanic landslides the results indicated four major features that play a significant role in such mass movements deep erosive canyons high coastal cliffs widespread residual soils and structural axes high coastal cliffs and deep erosive canyons locally reduce the stability conditions and control both the seaward and the lateral boundary of the landslide weak residual soils formed above phonolitic pyroclastic deposits occur repeatedly in the stratigraphic column of la orotava and are characterised by their large extent thus one of these soils may have evolved into the slip surface of the failure part of the head scarp of the amphitheatre is defined by a volcanic rift zone as indicated by the measurement of dike orientation and a density map of eruptive vents the four features are not able to trigger a failure but to destabilise the volcano flank and determine the boundary of the slide therefore information on depth and orientation of canyons location and height of coastal cliffs stratigraphic repetition extension and thickness of residual soils and orientation and density of dikes and eruptive vents along structural axes should be incorporated into a hazard assessment on large landslides on volcanic islands

offshore evidence for a huge landslide of the northern flank of tahiti nui french polynesia a bathymetric analysis of the flanks of tahiti nui french polynesia reveals the existence of a major catastrophic north directed landslide during its eruptive history the related debris avalanche da deposits extend north 70 km from the island shore and have a total volume of about 800 km3 two contrasted facies of the debris are recognized 1 relatively small sized material including a few blocks with well developed flow structures elongate downslope directed ridges and transversal pressure ridges and 2 a scattering of large kilometer sized individual blocks that form in part a prominent bathymetric hummock in the proximal central part of the landslide deposits bathymetric analyses suggest that the tahitian failure evolved through two main successive shots the da debris were rapidly overlain by subsequent volcanic material producing a smooth surface down to 1500 m below sea level the on land and offshore structures indicate a listric fault geometry for the landslide scar the volume removed by the landslide is thus estimated between 400 km3 and 450 km3 discrepancy in the volume of the scar and the debris derived from it is due in part to expansion of the debris to fragmentation of the avalanche and to incorporation of sediments comparison with a recently recognized southern tahitian landslide clouard et al 2001 and with landslides recognized around the hawaiian islands and the canary islands shows that the huge northern tahitian landslide described here has a reduced mobility in its central part perhaps the older tetiaroa eruptive complex to the north acted as a buttress to inhibit movement of the da products the northern and southern tahiti nui landslides moved in opposite directions away from the main central e w directed rift zone that served as the main magma feeding structure then the huge northern landslide strongly controlled the later volcano structural evolution by capturing subsequent volcanic activity to the north despite the northwestward displacement of the pacific plate over the society hot spot

morphology and origin of coastal karst landforms in miocene and quaternary carbonate rocks along the central western coast of sardinia italy in the area of punta funtanas arbus central west sardinia some small surfaces of miocene limestones crop out partially covered with quaternary calcarenites and plio quaternary basalts the biggest of these outcrops forms a fossil wave cut shore platform of up to 50 m wide with an altitude above sea level of approximately 4 5 m on this platform a wide variety of dissolution landforms can be observed these morphologies are related to the influence of the seawater zone of wave action marine splash and spray zone up to progressively more continental environments and to biokarst processes erosional action of marine organisms algae and micro organisms and are arranged in bands parallel to the coast corresponding to different morphological zones this paper describes all the karst landforms observed in this coastal area from a morphological and genetic point of view

a giant landslide on the north flank of tenerife canary islands the extent of mass wasting along the north flank of tenerife has been mapped using swath bathymetry gloria side scan sonar and 3 5 khz echo sounder data the marine surveys show that north of tenerife a giant landslide is exposed over an area of 5500 km2 of the seafloor more than twice the surface area of the island the landslide truncates an older ridge and valley topography that is associated with the shield building basalts on tenerife we interpret the ridge and valley topography as the result of subaerial erosion the landslide is estimated to have a length of 100 km a width of up to 80 km and a volume of about 1000 km3 it extends onshore into the orotava and icod valleys which have been interpreted as of landslide origin k ar dating of basaltic flows in the steep headwall of orotava suggests an age of formation for the valley is younger than 0 78 ma and may even be younger than 0 27 ma the icod valley is located immediately to the north of the most recent volcano on tenerife las canadas and has been associated with the collapse of its caldera between 1 2 and 0 2 ma a young age for the landslide is supported by the 3 5 khz echo sounder data which show that the landslide is draped by a thin 10 m layer of younger sediment the landslide did not form however during a single catastrophic event but represents the amalgamation of a number of separate landslides the occurrence of the ridge and valley topography in water depths of up to 2 5 km suggests that the shield building basalts have subsided by at least this amount since they formed 3 3 8 0 ma we speculate that this subsidence is caused by some form of stress relaxation that occurs in the underlying lithosphere the giant landslide imaged in our sonar data is associated with the late stages in the development of the most recent volcano on tenerife las canadas which only began at about 1 8 ma thus landsliding may be a particular feature of the time soon after emplacement when because of incomplete isostatic adjustment oceanic volcanoes have their greatest elevations above sea level and therefore are most susceptible to slope failure

karst pocket valleys and their implications on pliocene quaternary hydrology and climate examples from the nullarbor plain southern australia abstract karst on the nullarbor plain has been studied and described in detail in the past but it lacked the determination of the karst discharge and palaeo watertable levels that would explain the palaeohydrological regime in this area this study explores the existence of previously unrecognised features in this area karst pocket valleys and gives a review on pocket valleys worldwide initial gis analyses were followed up by detailed field work sampling mapping and measuring of morphological geological and hydrological characteristics of representative valleys on the wylie and hampton scarps of the nullarbor plain rock and sand samples were examined for mineralogy texture and grain size and a u pb dating of a speleothem from a cave within a pocket valley enabled the establishment of a time frame of the pocket valleys formation and its palaeoenvironmental implications the pocket valleys document the hydrological evolution of the nullarbor karst system and the neogene pleistocene palaeoclimatic evolution of the southern hemisphere a review of pocket valleys in different climatic and geological settings suggests that their basic characteristics remain the same and their often overlooked utility as environmental indicators can be used for further palaeoenvironmental studies the main period of intensive karstification and widening of hydrologically active underground conduits is placed into the wetter climates of the pliocene epoch subsequent drier climates and lowering of the watertable that followed sea level retreat in the quaternary resulted in formation of the pocket valleys gravitational undermining slumping exudation and collapse which combined with periodic heavy rainfall events and discharge due to impeded drainage caused the retreat of the pocket valleys from the edge of escarpments

stratigraphy of the bandas del sur formation an extracaldera record of quaternary phonolitic explosive eruptions from the las canadas edifice tenerife canary islands explosive volcanism has dominated the large phonolitic shield volcano of tenerife the las canadas edifice for the last 1 5 m y pyroclastic deposits of the bandas del sur formation are exposed along the southern flanks and record the last two of at least three long term cycles of caldera forming explosive eruptions each cycle began with flank fissure eruptions of alkali basalt lava followed by minor eruptions of basanite to phonotephrite lavas minor phonotephritic to phonolitic lava effusions also occurred on the flanks of the edifice during the latter stages of the second explosive cycle non welded plinian fall deposits and ignimbrites are the dominant explosive products preserved on the southern flanks of these a significant volume has been dispersed offshore many pyroclastic units of the second explosive cycle exhibit compositional zonation banded pumice occurs in most units of the third youngest explosive cycle and ignimbrites typically contain mixed phenocryst assemblages indicating the role of magma mixing mingling prior to eruption at least four major eruptions of the third cycle began with phreatomagmatic activity producing lithic poor accretionary lapilli bearing fallout and or surge deposits the repeated brief phase of phreatomagmatism at the onset of these eruptions is interpreted as reflecting an exhaustive water supply probably a small caldera lake that was periodically established during the third cycle accidental syenite becomes an increasingly important lithic clast type in ignimbrites up sequence and is interpreted as recording the progressive development of a plutonic complex beneath the summit caldera successive eruptions during each explosive cycle increased in volume with the largest eruption occurring at the end of the cycle more than ten major explosive eruptions vented moderately large volumes 1 ges 10 km 3 of phonolitic magma during the last two cycles culminating each explosive cycle was the emplacement of relatively large volume 5 10 km 3 ignimbrites with coarse vent derived lithic breccias interpreted to record a major phase of caldera collapse in the extracaldera record explosive cycles are separated by 0 2 m y periods of non explosive activity repose periods were characterized by erosion remobilization of pyroclastic deposits by discharge events and pedogenesis the current period of non explosive activity is characterized by the construction of the teide pico viejo stratovolcanic complex within the summit caldera this suggests that eruptive hiatuses in the extracaldera record may reflect effusive activity and stratovolcano or shield building phases within the summit caldera alternating effusive and explosive cycles have thus been important in the volcanic evolution of the las canadas edifice

susceptibility of mid ocean ridge volcanic islands and seamounts to large scale landsliding 1 with a view to assessing the incidence of large scale landsliding a morphologic database was created for volcanic islands and seamounts on young oceanic lithosphere the database included 44 mid ocean ridge seamounts jasper seamount and the islands of ascension bouvet guadalupe and several of the galapagos and azores islands supplemented with published reports from a further five volcanic edifices the data reveal that major landslides are common on edifices taller than 2500 m but are rare in shorter edifices implying a threshold of instability at around 2500 m a number of causes of this threshold are discussed for example many structures taller than 2500 m are or were originally volcanic islands and therefore their flanks probably include extensive weak hyaloclastite built up from lava sea interactions around coasts compaction of hyaloclastites in larger edifices lead to regions of low permeability which may help to explain the more deeply seated slope failures it is intriguing that the threshold also coincides with the edifice height at which volcanic ridges become observable a stage at which dike intrusion is probably common because slope oversteepening or excess pore pressure associated with dike intrusions have been proposed elsewhere as landslide triggers the current indications of landsliding reveal no observable relation to rainfall as landslides occur equally in wet and dry climates and no relation to tectonic setting as there are relatively few major landslides in the seismically active azores group

growth and persistence of hawaiian volcanic rift zones hawaiian volcanic rift zones are modeled by representing the rifts and adjacent volcano flanks as long ridges with the geometry of flattened triangular prisms the intrusion of dikes along the axis of a rift requires a mechanism to generate the appropriate dike trapping stress field within the prism possible factors that affect the state of stress in the prism include multiple dike intrusion along the ridge axis faulting and gravitational sagging of the topography in extreme models with very steep slopes and high poisson s ratio corresponding to the gelatin models of rift zones by fiske and jackson 1972 results of finite element calculations indicate that gravity induced stresses are sufficient to trap a dike into propagating within the prism and parallel to the rift zone as proposed by fiske and jackson however the mechanism does not work for gently sloping flanks or a more acceptable poisson s ratio of about 0 25 additionally trapping stresses in the gravity loading and density stratification models will not persist after a few dike injection episodes therefore in mature hawaiian rift zones with possibly thousands of dikes additional processes must act to control the stresses that permit continued dike intrusion and rift persistence it is proposed that accommodation to dike emplacement occurs by slip on deep faults possibly of the type proposed for the 1975 kalapana hawaii earthquake as suggested by others for this earthquake the faults could coincide with the contact of the volcano with the seafloor within the weak seafloor sediments such faulting not only provides a means for the flanks to adjust continuously to intrusions but also generates the stress patterns needed to constrain future dikes to propagate along the rift axis other possible faulting mechanisms such as shallow gravity slides and normal faulting of the flanks do not appear to favor rift zone persistence in this model the horizontal stress generated by a standing column of magma at the time of dike emplacement the stresses in the ridges and the fault strength are coupled this results in a feedback between the maximum height that magma can rise along the rift fault friction and fault width through this feedback the slope of the volcano flank is controlled by the fault friction when applied to kilauea volcano the model yields an estimate for the coefficient of fault friction as high as 0 39 assuming normal hydrostatic pore fluid pressure an implication of this model supported by other studies is that rift intrusion and lateral spreading could be major contributors to volcano growth

importance of gravitational spreading in the tectonic and volcanic evolution of mount etna the interaction between gravity and thermal effects largely determines the structural and magmatic evolution of volcanic constructs at scales spanning several orders of magnitude from small cones to the oceanic crust1 3 although gravitational spreading is a direct consequence of this interaction and a fundamental process in volcano growth it is rarely recognized as such here we describe a striking example of this process at etna volcano in italy the volcano and its clay rich substratum are slowly spreading towards the east and south driven by gravity spreading produces extensional structures in the summit region and contpressional structures at the base of the volcano eastward movement of the volcanic edifice over a stationary magma supply may be the cause of an apparent westward migration of volcanic activity as gravitational spreading seems to control the location and magnitude of shallow seismicity and flank eruptions an appreciation of its effects could become an essential element of future volcanic hazard evaluation our model proposed here for etna may also be relevant to a reinterpretation of the geological history of a number of other volcanoes

roots rock and regolith biomechanical and biochemical weathering by trees and its impact on hillslopes a critical literature review the role of trees and forests as a critical component of the biosphere and critical zone and of the earth system more generally is widely appreciated less known and acknowledged are the geomorphological functions of tree roots although their importance has been widely referred to in soil studies paleopedology and paleobotany tree roots and their impact on weathering processes and soil production were incorporated in the devonian plant hypothesis and tree root casts served as a key evidence of recognition of past soils in geology sedimentology and paleopedology however knowledge of biomechanical and biochemical weathering induced by vascular plant roots mainly trees has been rarely utilized in geomorphic studies biogeomorphic and pedologic studies in recent decades have highlighted the importance of tree uprooting in which roots play a primary role in soil development regolith disturbance and bedrock mining other important functions of roots were also recognized e g soil displacement by growing roots infilling of stump holes and root cavities root groove development direct and indirect effects taking place in the rhizosphere and mycorrhizosphere mainly biochemical weathering of minerals support by microbial communities and symbiotic fungi and changes in porosity permeability and hydrology of soils in the root zone however further studies are urgently needed because many aspects of biochemical and biomechanical weathering are not well understood this is especially true with respect to taxa specific impacts variations in root architectures edaphic settings ecological relationships and geographic ranges result in substantially different biogeomorphic impacts of different tree species additionally the same species in different environmental settings may have different effects

chronology of quaternary coastal aeolianite deposition and the drowned shorelines of southwestern western australia a reappraisal abstract aeolianite successions of low gradient continental margins commonly show complex records of coastal dune deposition linked to a wide range of sea level positions and climatic periods of the middle and late pleistocene recording both regional and broader scale drivers of sediment production coastal dune development and landform preservation to better characterise the general pattern of sedimentation that occurs over quaternary glacial interglacial cycles on low gradient temperate carbonate continental shelves we examine the morphology stratigraphy and age of aeolianite deposits in the perth region western australia this includes an analysis of well defined drowned coastal landforms preserved on the adjacent shelf new and previously published optical ages provide a preliminary timeframe for the deposition of aeolianite in the perth region and on rottnest island 17 km offshore an extensive aeolianite ridge near perth representing a former barrier has optically stimulated luminesence osl ages that range from 120 12 to 103 10 ka mis 5e 5a in the context of associated age uncertainties osl ages for an exposure in the same ridge 2 5 km inland record the onlap of much older aeolianite osl age 415 70 ka by shell rich estuarine beds osl age 290 30 ka a further 5 5 km inland from the coast two thick aeolianite units separated by a well developed palaeosol have stratigraphically consistent osl ages of 310 30 and 155 20 ka in contrast aeolianite units that form the northern coast of rottnest island have osl ages of 77 12 ka and 27 5 ka the new osl ages and previously reported tl and u th ages indicate that the bulk of the island comprises dunes deposited around the end of the last interglacial sensu lato mis 5a 4 and during the last glacial mis 4 2 accumulating over a last interglacial coral reef and basal calcarenite drowned barrier and dune landforms preserved on the adjacent continental shelf reveal that barriers were formed during periods of intermediate sea level e g mis 3 and significant dune mobility occurred when the shelf was subaerially exposed the pattern of shelf sedimentation discernible in the perth region large scale coastal carbonate dune deposition during periods of high and intermediate sea level and reactivation during glacial lowstands is largely consistent with published stratigraphic and age data for large scale aeolianite deposits on other low gradient carbonate shelves based on these data a general model is proposed for the cycle of quaternary sedimentation and landform evolution that occurs on these shelves which are dynamic sedimentary environments with coastal landforms and sedimentary successions that are very sensitive to erosion and sediment reworking

the formation of the pinnacle karst in pleistocene aeolian calcarenites tamala limestone in southwestern australia abstract a spectacular pinnacle karst in the southwestern coastal part of western australia consists of dense fields of thousands of pinnacles up to 5 m high 2 m wide and 0 5 5 m apart particularly well exposed in nambung national park the pinnacles have formed in the pleistocene tamala limestone which comprises cyclic sequences of aeolian calcarenite calcrete microbialite and palaeosol the morphology of the pinnacles varies according to the lithology in which they have formed typically conical in aeolianite and cylindrical in microbialite detailed mapping and mineralogical chemical and isotopic analyses were used to constrain the origin of the pinnacles which are residual features resulting mainly from solutional widening and coalescence of solution pipes within the tamala limestone the pinnacles are generally joined at the base and the stratigraphy exposed in their sides is often continuous between adjacent pinnacles some pinnacles are cemented infills of solution pipes but solution still contributed to their origin by removing the surrounding material although a number of pinnacles contain calcified plant roots trees were not a major factor in their formation pinnacle karst in older better cemented limestones elsewhere in the world is similar in morphology and origin to the nambung pinnacles but is mainly influenced by joints and fractures not evident at nambung the extensive dissolution associated with pinnacle formation at nambung resulted in a large amount of insoluble quartz residue which was redeposited to often bury the pinnacles this period of karstification occurred at around mis 5e and there was an earlier less intense period of pinnacle development during mis 10 11 both periods of pinnacle formation probably occurred during the higher rainfall periods that characterise the transition from interglacial to glacial episodes in southern australia the extensive karstification around mis 5e indicates that the climate was particularly humid in southwestern australia at this time

an experimental investigation of the mechanical behavior and microstructural features of a volcanic soil isparta turkey and stability of cut slopes in this soil abstract volcanic soils are widely distributed group of soils which cover significant parts of the world s surface and include areas occupied by urban settlements structures and infrastructures and may create geo engineering problems these soils exhibit a distinctive behaviour that is a consequence of their formation history mineralogy and structure some part of the subsoil of a large area surrounding the city of isparta western turkey mainly consists of volcaniclastic deposits this paper presents the results of the part of a research programme aiming at geotechnically characterizing the uppermost layer of this volcaniclastic sequence particularly focusing on its collapse potential shear behaviour and the influence of microstructure on these behaviours in addition its main futures were compared with those of some similar volcanic soils at different parts of the world and the stability of sub vertical cuts in this soil was also assessed the experimental investigation mainly consisted of index and classification tests double oedometer and direct shear box tests to assess the collapse potential and shear behaviour of the soil respectively matric suction of the samples was also determined for preliminary evaluation of the influence of suction on collapse and shear behaviours of the soil in addition thin section studies and x ray diffraction xrd and scanning electron microscopy sem analyses were also conducted to determine mineralogical and microstructural features and to evaluate their influences on the mechanical behaviour of the volcanic soil the deposit is composed of weakly bonded firm silty sand with an open structure low unit weight and high porosity generally unsaturated in situ the results of the double oedometer tests suggest that the volcanic soil generally falls in the category of slight collapse potential at normal stresses ranging between 5 and 100 kpa while at normal stresses greater than 100 kpa its collapse potential increases and ranges between moderate and moderately severe collapse potential classes at normal stresses lower than 100 kpa matric suction may have an effect on collapse behaviour the direct shear box test results indicated that the volcanic soil has two different types of shear strength behaviour represented by bi linear failure envelopes in other words the shear strength parameters of the volcanic soil within a low normal stress range generally between about 6 and 200 kpa exceed those of determined at higher normal stresses since no matric suction was measured during the direct shear box tests it could not be possible to evaluate the effect of suction on the bi linear failure envelopes however some differences between the suction and degree of bonding of the samples taken from different locations might probably have been contributed to the separation of the bi linear behaviour at different normal stress levels the destruction of the bonding cementation between the particles is probably more responsible from the bi linear form of the failure envelope comparisons between the sem micrographs taken from natural and tested specimens revealed that the mechanical behaviour of the volcanic soil is strongly influenced by the bonding material the results of the stability analyses showed a good agreement with the current situation of the cut slopes observed in the study site and suggested that vertical cut slopes with a height of 14 15 m will maintain their stability based on a reasonable factor of safety such as 1 5

assessing channel response of a long river influenced by human disturbance article i nfo this paper describes an approach to assess channel changes of a long anthropogenised river the middle loire river over decadal timescales channel changes are evaluated along geomorphically homogeneous river reaches the classic geomorphic parameters active channel width bed slope grain size are complemented with parameters extracted from a 1d hydraulic model width depth ratio effective bed shear stress and specific stream power calculated for the biennial discharge assimilated to bankfull flow conditions the delineation of reaches is undertaken by combining visual inspection with the implementation of simple statistical tests to corroborate discontinuities in flow and sediment transport the 450 km long study area has been divided into 167 homogeneous reaches the general trends observed over the last fiftyyearsarenarrowingoftheactivechannel width and incision of the river bed however changes in bed level and active channel width are not consistently correlated channel changes at the reach scale are mainly controlled by the presence of former sediment extraction sites significant incision is observed at the peak of the in stream sediment mining period this was followed by channel recovery when extractions stopped the 1d numerical model provides a more rigorous manner to derive hydraulic parameters the effective bed shear stress made dimensionless by its critical value and the width depth ratio helps to explain observed channel responses more effectively by relating patterns to geological units along the middle loire

turbidite record of frequency and source of large volume 100 km3 canary island landslides in the last 1 5 ma implications for landslide triggers and geohazards during the last two decades numerous studies have focused on resolving the landslide histories of the canary islands issues surrounding the preservation and dating of onshore and proximal submarine landslide deposits precludes accurate determination of event ages however submarine landslides often disaggregate and generate sediment gravity flows volcaniclastic turbidites sampled from madeira abyssal plain piston cores represent a record of eight large volume failures from the western canary islands in the last 1 5 ma during this time there is a mean recurrence rate of 200 ka while the islands of el hierro and tenerife have individual landslide recurrences of 500 ka and 330 ka respectively deposits from the 15 ka el golfo landslide from el hierro and 165 ka icod landslide from tenerife are examined this study also identifies potential deposits associated with the orotava 535 ka guimar 850 ka and rogues de garcia landslides 1 2 ma from tenerife el julan 540 ka and el tinor 1 05 ma landslides from el hierro and the cumbre nueva landslide 485 ka from la palma seven of eight landslides occurred during major deglaciations or subsequent interglacial periods which represent 55 of the time however all of the studied landslides occur during or at the end of periods of protracted island volcanism which generally represent 60 of the island histories although climate may precondition failures it is suggested that volcanism presents a more viable preconditioning and trigger mechanism for canary island landslides

500 ka precipitation record from southeastern australia evidence for interglacial relative aridity 230 th 234 u dating of speleothems from southeastern australia documents changes in effective precipitation over the past 500 k y at a temporal resolution not previously achieved results show that the highest effective precipitation for the southeastern interior of australia occurred during stadials and cool interstadials of the past four glacial cycles interglacials and warm interstadials as well as glacial maxima are comparatively arid we suggest that lower regional temperatures over the continent and changes in atmospheric circulation stronger walker circulation produced the observed periods of increased effective precipitation

volcanic dry avalanche deposits identification and comparison with nonvolcanic debris stream deposits abstract a volcanic dry avalanche deposit is defined as a volcaniclastic deposit formed as a result of a large scale sector collapse of a volcanic cone associated with some form of volcanic activity avalanche transport occurred in response to the gravitational field in a manner similar to the transport of nonvolcanic debris streams e g hsu 1975 such deposits are characterized by megablock structure deformed and fractured large blocks up to several hundreds meters in diameter a megablock preserves original layering intrusive contacts or weathered surfaces of the source volcanic edifice surface topography of the deposit is characterised with hummocky relief ratios of fell height to travel distance for volcanic dry avalanche deposits are between 0 18 and 0 06 this range is similar but smaller than the value of 0 58 to 0 08 for nonvolcanic debris stream deposit this similarity suggests similar transportation mechanisms excessive travel distances as defined by hsu 1975 calculated for volcanic dry avalanche deposits give values larger than for debris stream deposits of the same volume the difference is explained by lower rigidity of the collapsing mass due to the existence of soft pyroclastic layers alteration around the vent development of fractures owing to new cryptodome intrusion and boiling of supercritical fluid contained within the collapsed mass

the genesis of solution pipes evidence from the middle late pleistocene bridgewater formation calcarenite southeastern australia abstract solution pipes are abundant in late pleistocene aeolian calcarenites at cape bridgewater in southwestern victoria and were studied using field work morphometric analysis thin sections mineralogical and chemical analyses and osl dating the solution pipes are vertical tubes formed in aeolian limestone with matrix porosity they are typically 0 1 1 m wide and 1 5 m deep with rounded terminations and cemented rims up to 10 cm thick they are overlain by palaeosols and filled mostly with palaeosol material rhizoliths are commonly present in the solution pipe fills and the surrounding calcarenite the solution pipes have formed by focused dissolution of aeolianite relatively quickly after the sand deposition and concurrently filled with soil as they developed they most likely formed beneath trees as a result of focused infiltration due to stemflow or due to fingered flow unstable wetting front that breaks into fingers as it moves downwards solution pipe formation was strongly dependent on climate periods of solution pipe formation followed the deposition of aeolianites at the end of interglacials mis 7 9 and 11 when the dunes were stabilised by vegetation and there was sufficient rainfall for substantial subsoil dissolution the cemented rims formed in the following drier glacial climates solution pipes are most abundant in the youngest aeolianite probably reflecting the wetter climate at the end of mis 7 that allowed a dense forest to cover the dunes from mis 5 to mis 2 no deposition of calcareous sand occurred on cape bridgewater and combined with a very wet interglacial period mis 5e resulted in additional karstification allowing the pipes in the mis 7 aeolianite to extend deeper and drill down into the underlying member a well developed calcrete layer drapes over these solution pipes and probably formed during the dry windy climate of the last glacial maximum

new quartz sar osl ages from the stranded beach dune sequence in south east south australia a sequence of stranded coastal barriers in south east south australia preserves a record of sea level variations over the past 800 ka huntley et al quat sci rev 12 1993a 1 quat sci rev 13 1994a 201 attempted to test thermoluminescence tl dating methods and found good agreement between quartz tl ages with independent ages for these dunes we investigate the accuracy of the single aliquot regenerative dose sar procedure radiat meas 32 2000 57 over an extended age range of 0 250 ka by comparing sar osl ages determined on quartz extracts from these dunes with the existing chronology we show that robe ii range is 60 ka and that robe iii is 100 ka old not surprisingly the osl ages increase monotonically from the robe ii range to the west naracoorte range for the younger dunes 240 ka the sar osl ages agree with the expected ages within 1 errors whereas for the older dunes the sar ages are consistent with independent ages within 2 error limits we consider these results to be very promising and lend support to the large number of quartz sar osl ages being presented in the literature where such comparisons with independent chronology are not usually possible

conditions favouring catastrophic landslides on tenerife canary islands catastrophic failures of volcano flanks represent one of the most hazardous geological phenomena these immense mass movements originate either by increasing the destabilizing forces driving forces or by reducing the strength of the materials involved or both the study of large volcanic landslides on tenerife suggests that the presence of weak residual soils palaeosols in combination with the pre existence of deep narrow canyons created by fluvial erosion have played a fundamental role in the initiation of large scale sector collapses of the volcanic edifice regardless of the triggering mechanism considered residual soils strongly reduce the material strength during undrained loading while pre existing canyons control the lateral limits of the landslide the existence of a wet climate in some sectors of the island favours these circumstances

river response to channel regulation case study of the raba river carpathians poland processes induced by the channelization of the raba river in the present century are examined to illustrate the response of a gravel bed stream following narrowing and straightening of its channel up to 3 m of incision has occurred the change from a slow and relatively steady degradation in the lower reaches to separate degradation events in the higher reaches is attributed to the differential rate of headcut retreat and to the control exerted by mid channel bars upon the rate of river energy dissipation progressive outwashing of finer grains from bed material has followed the diminishing sediment yield of the basin and the increase in stream power the ensuing growth in mean grain size and changes in sediment fabric have increased boundary resistance to flow and reduced particle susceptibility to entrainment downstream magnification of peak discharges has become increasingly pronounced with the advancing incision the decrease in flood plain storage and self acceleration of flows passing the relatively deep and straight channel has caused flood waves to become progressively more flashy in nature an increase in channel depth and reduction in gradient caused by downward and backward erosion as well as bed material coarsening has promoted the re establishment of an equilibrium conversely flow velocity increases due to flow concentration in the deepened channel reduction in grain mobility allows the river to attain a new equilibrium at flow velocity and stream power levels higher than before the channelization numerous disadvantages of the applied regulation scheme and its failure to reduce flood hazard raise the question of its maintenance to be successful any regulation design must take into account changes in sediment supply and flood hydrographs resulting from the simultaneous alterations in basin management

fluvial geomorphological analysis of the recruitment of large woody debris in the yalobusha river network central mississippi usa abstract the management of large woody debris lwd should be based on a rational assessment of its recruitment rate relative to its natural decay and removal lwd recruitment may be controlled by natural episodic terrestrial factors or by in channel geomorphological controls related to the rate of bank erosion the geomorphological controls are hard to quantify in laterally migrating channels but in incising channels a conceptual model may be developed based on the density of riparian trees relative to the knickpoint migration rate and bank stability analyses that predict the post knickpoint width of the channel the yalobusha river network in central mississippi usa has twice been destabilised by channel straightening for flood defence and land drainage most recently in 1967 system wide rejuvenation has followed through a series of upstream migrating knickpoints several metres high that have caused mass failure of streambanks and the recruitment of large volumes of trees to the channel lwd recruitment is maximised at the transition between stage iii and stage iv channels focusing attention on 11 sites in the network the sites are upstream of knickzones ranging between 2 2 and 5 4 m high and migrating at rates of 0 13 8 m year 1 based on 23 30 months of monitoring riparian conditions in 500 m2 plots on each bank upstream of the knickpoints range from treeless to forested containing 0 98 trees with an average diameter at breast height of 0 18 m and average maximum height of 14 0 m the average volume of wood on each bank is 0 02 m3 m 2 under rapid drawdown conditions bank stability analyses suggest that the channels will widen in amounts ranging from 1 8 to 31 5 m combined with the knickpoint migration rates riparian land losses are estimated to range from 8 0 to 433 8 m year 1 resulting in the recruitment of almost 28 m3 of wood or 100 trees annually from the 11 sites assuming this lwd recruitment rate a model is developed for the in situ potential for debris dam initiation and growth based on the ratio of tree height to channel width under current and post knickpoint conditions the annual delivery of large trees and the annual total of lwd recruitment by volume a longer term model is also developed based on knickpoint severity and vegetation density in upstream and headwater riparian zones of each tributary the 11 study sites are classified into groups with similar lwd management concerns based on these analyses the models developed in this research provide the first precise quantification of lwd recruitment according to geomorphological controls and standing vegetation and a rational assessment of its meaning but further research is required to improve the accuracy of such estimates

rifting recurrent landsliding and miocene structural reorganization on nw tenerife canary islands we studied mechanisms of structural destabilization of ocean island flanks by considering the linkage between volcano construction and volcano destruction exemplified by the composite teno shield volcano on tenerife canary islands during growth tenerife episodically experienced giant landslides genetically associated with rifting and preferentially located between two arms of a three armed rift system the deeply eroded late miocene teno massif allows insights into the rifting processes the failure mechanisms and related structures the semicircular geometry of palaeo scarps and fracture systems breccia deposits and the local dike swarm reconfigurations delineate two clear landslide scarp regions following an earlier collapse of the older los gigantes formation to the north the rocks around the scarp became fractured and intruded by dikes substantial lava infill and enduring dike emplacement increased the load on the weak scarp and forced the flank to creep again finally resulting in the collapse of the younger carrizales formation once more the changing stress field caused deformation of the nearby rocks a fracture belt formed around the scarp and dikes intruded into new concentric directions the outline size and direction of the second failed flank of teno very much resembles the first collapse we suggest structural clues concerning mechanisms of recurrent volcano flank failure verifying the concept that volcano flanks that have failed are prone to collapse again with similar dimensions

geomorphic response of lillooet river british columbia to meander cutoffs and base level lowering abstract a detailed record of channel profiles slopes and stream discharge on lillooet river provides an opportunity to study the effects of natural and artificial channel changes that have occurred over the past century we analyze the long term effects of channel alterations that may affect flood hazard in the mid 1940s several meanders were artificially severed side channels blocked off and the level of downstream lillooet lake was lowered these measures were thought to increase hydrologic efficiency and decrease flood risk in the largely agricultural valley between 1947 and 1994 average channel width in the upper reaches decreased by 50 most of which occurred by the late 1950s between 1945 and 1969 lillooet river degraded its bed elevation by 3 4 m 12 5 to 16 7 cm a 1 in the upper reaches and up to 2 m 8 3 cm a 1 in the lower reaches this sudden and profound degradation compares to average bed elevation increases of 2 4 cm a 1 prior to the engineering works between 1969 and 1985 the cross section area increased by 22 in the upper reaches and 13 in the lower reaches and decreased to 12 and 8 respectively for the time period 1985 to 2000 the increased sediment supply that was caused by channel straightening accelerated delta advance in lillooet lake from 7 m a 1 1858 to 1948 to 30 m a 1 for the five year period following the 1948 channel works these rates have decreased over time but with a current advance rate of 10 5 m a 1 1986 2009 are still above the long term average prior to the channel changes this study demonstrates the time scale direction and magnitude of channel changes following significant artificial river alterations while the initial goal of decreasing flood risk had been achieved in the short term the lower river apparently is slowly returning to an overall aggradational phase ongoing delta advance will ultimately increase channel elevations in the lower reaches and lead to significant flood hazards for populated areas

a criticism of the proposed regional extent of late cenozioc arid zone advances into south western australia summary geomorphological sedimentological evidence for late cenozoicarid zone extensions is widespread in western australia however their regional extent into the extremes of southwestern australia is in dispute it has been suggested that a widespread coastal yellow sand facies is a desert eolian sediment indicative of arid zone advances into this region the claim is examined through a comparison of grain size characteristics grain surface textures and field relationships of coastal and inland sands

lower eocene carbonate cemented chimneys varna ne bulgaria formation mechanisms and the a biological mediation of chimney growth abstract in the area of pobiti kamani varna northeast bulgaria massive carbonate cemented columns chimneys up to 1 5 m diameter and 8 m high and horizontal interbeds 1 5 m thickness occur in dispersed outcrops over an area of 70 km2 within loose lower eocene sands field observations and petrographical and stable isotope geochemical characterisation of four studied locations reveal a relationship between these structures and processes of ancient hydrocarbon seepage column and interbed structures both consist of similar well sorted silt to sand sized nummulitic host sediments predominantly cemented by early diagenetic low magnesium calcite filamentous textures about 10 m in diameter and 80 650 m long are only locally detected within interparticle calcite cement of columns column samples from two sites reveal a similar linear and inverse covariant trend of 13c 18o values which was interpreted as a mixing trend between two end member fluid precipitation conditions i e 1 a methane and or higher hydrocarbon derived carbon member characterised by 13c values as low as 43 and marine controlled precipitation conditions with 18o of 1 0 5 v pdb and 2 a member with less contribution of methane which was mixed most likely with less depleted carbon sources explaining 13c values ranging up to 8 v pdb the corresponding depleted 18o values with many samples clustering around 8 v pdb are interpreted in terms of precipitation at elevated temperatures this suggests the venting system was not a true cold seep sensu stricto furthermore column cross transects often document an internal pattern consisting of concentric zones with distinct isotopic signatures which vary between the two end members the mixing and internal pattern of column isotopic data together with petrographical observations are qualitatively interpreted as evidence of alternating precipitation conditions controlled by varying seepage rates of a single fluid source at depth during build up of individual chimney pipes near the sediment surface based on several field observations migration of the hydrocarbon charged fluids in lower eocene times was possibly channelled along ne oriented faults isotopic signatures of calcite cemented horizontal interbeds with depleted 18o ratios as low as 8 88 v pdb and variable 13c 1 to 16 mainly around 5 to 7 suggest that ascending fluids contributed to their cementation or resetted the calcite cement isotopic signature predominantly during periods of active seepage of warmer fluids only few petrographical and preliminary lipid biomarker evidence has been found pointing to the presence or possibly former activity of microbiota involved in carbon cycling and calcite precipitation typical of cold seep settings this may result from diagenetic alteration of organic components however considering the processes of chimney formation a cementation process governed by the inorganic oxidation of hydrocarbons in which interstitial oxygen is rapidly consumed without bacterial mediation is considered

geomechanical parameters of intact rocks and rock masses from the canary islands implications on their flank stability abstract new data on the geomechanical properties of the highly cohesive volcanic rocks of the canary archipelago and their role in the flank stability on oceanic islands are provided in this work on the basis of the textural and petrological features a preliminary classification of rocks grouped into lithotypes was carried out this classification includes vesicular and non vesicular basalts trachybasalts trachytes phonolites welded and non welded ignimbrites strength and strain related features are summarized here for each distinctive lithotype taking into account the results of the uniaxial and triaxial compressive tests the geological strength index of rock masses and their textural structural features an estimate of the rock mass parameters and mohr coulomb fit has been carried out a final discussion on the impact of those geomechanical parameters as factors governing the stability of steep slopes in volcanic islands is then made here as a contribution in volcanic risk

evolution of the north flank of tenerife by recurrent giant landslides geomorphologic analysis of submarine and subaerial surface features using a combined topographic bathymetric digital elevation model coupled with onshore geological and geophysical data constrain the age and geometry of giant landslides affecting the north flank of tenerife shaded relief and contour maps and topographic profiles of the submarine north flank permit the identification of two generations of post shield landslides older landslide materials accumulated near the shore 40 km and comprise 700 km3 of debris thickening towards a prominent axis suggests one major landslide deposit younger landslide materials accumulated 40 70 km offshore and comprise the products of three major landslides the la orotava landslide complex the icod landslide and the east dorsal landslide complex each with an onshore scar a proximal submarine trough and a distal deposit lobe estimated lobe volumes are 80 80 and 100 km3 respectively the old post shield landslide scar is an amphitheatre 20 25 km wide partly submarine now completely filled with younger materials age width relationships for tenerife s coastal platform plus onshore geological constraints suggest an age of ca 3 ma for the old collapse young landslides are all less than 560 ka old the la orotava and icod slides involved failures of slabs of subaerial flank to form the subaerial la orotava and icod valleys offshore they excavated troughs by sudden loading and basal erosion of older slide debris the onshore east dorsal slide also triggered secondary failure of older debris offshore the slab like geometry of young failures was controlled by weak layers deep drainage channels and flank truncation by marine erosion the partly submarine geometry of the older amphitheatre reflects the absence of these features relatively low h l ratios for the young slides are attributed to filling of the slope break at the base of the submarine edifice by old landslide materials low aspect ratios of the failed slabs and channelling within troughs post shield landslides on tenerife correlate with major falls in sea level reflecting increased rates of volcanism and coastal erosion and reduced support for the flank landslide head zones have strongly influenced the pattern of volcanism on tenerife providing sites for major volcanic centres

modelling the 14c bomb pulse in young speleothems using a soil carbon continuum model abstract the bomb pulse method is a chronological approach to further constrain the age of speleothems that grew between 1950 ce present establishing dependable chronological constraints is crucial for modern calibration studies of speleothems to instrumental climate records which provides the basis for paleoclimate interpretations however a large unknown is how 14c is transferred from the atmosphere to any individual speleothem owing to the site specific residence times of organic matter above cave systems here we employ the bomb pulse method to build chronologies from 14c measurements in combination with a new unsaturated zone c model which considers c decomposition as a continuum to better understand unsaturated zone 14c dynamics the bomb pulse curves of eight speleothems from southern australia in three contrasting climatic regions the semi arid wellington caves site the mediterranean golgotha cave site and the montane yarrangobilly caves site are investigated overall the modelled 14c bomb pulse curves produce excellent fits with measured 14c speleothem data r2 0 82 0 99 the c modelling reveals that unsaturated zone c is predominately young at the semi arid site with a weighted mean residence time of 32 years and that tree root respiration is likely an important source of vadose co2 at the montane site 39 of c is young

multiphase breakdown sequence of collapse doline morphogenesis an example from quaternary aeolianites in western australia abstract the morphology of collapse dolines varies according to their maturity and effectiveness of the removal of collapsed material in addition the variable balance between various geomorphic processes due to local geologic hydrologic and climatic settings results in a diverse morphology of collapse dolines and dynamics of their morphogenesis a single generalised proposed sequence of collapse dolines morphogenesis has therefore limited value and more detailed study is needed in terrains which differ in terms of geology hydrology and or climate there is a particularly well exposed karst in stockyard gully national park in the southwestern coastal part of western australia formed in quaternary aeolianites consisting of a dense field of collapse dolines up to 100 m in diameter and on average 10 m deep extensive field work combined with available data of local rock stratigraphy and a comparison to collapse dolines worldwide revealed that the principal processes of collapse doline formation in stockyard gully national park are similar to processes responsible for collapse doline formation worldwide i e collapses above underground chambers and removal of the collapsed material however rock characteristics in the area influence their morphometry due to the mechanical weakness of aeolianite compared to well cemented limestones and a surface calcrete layer with stronger mechanical resistance than underlying aeolianite consequently we propose a new 4 stage multiphase breakdown sequence of collapse doline morphogenesis in aeolianites divided into cave dome calcrete caprock dome young collapse doline and mature collapse doline calcrete caprock dome is stabilised by the uppermost well cemented calcrete and represents a distinctive phase just before the final breakdown to form an actual collapse doline

identifying dynamic equilibrium of an undeveloped alluvial stream by extremal hypotheses abstract the indeterminate channel problem arises from uncertainty in finding a closure relation for alluvial channels created by self organizing erosional and depositional processes extremal hypotheses have been proposed as one potential approach to closing the system of governing equations for alluvial channels many different extremal hypotheses have been presented but no substantive evidence has been developed to select which hypothesis may be most appropriate for natural alluvial river systems this paper evaluates the ability of ten extremal hypotheses to identify dynamic equilibrium across a geomorphic gradient in the remote and undeveloped mid latitude watershed of rio murta chile this study a introduces extremal hypotheses b describes the field site and geomorphic conditions and c examines which extremal hypotheses are supported by the field data in identifying the evolutionary trend toward dynamic equilibrium the extremal hypotheses that identified dynamic equilibrium within the geomorphic gradient in the field are 1 minimum kinetic energy 2 minimum specific stream power 3 maximum friction factor and 4 maximum total friction factor which collectively support minimizing kinetic energy of the system

causes of planform stability of a low energy meandering gravel bed river cher river france abstract for at least two centuries the lateral mobility of the meandering reaches of the cher river france has been very low this article aims to identify the main causes of this behavior two not mutually exclusive explanatory hypotheses are proposed under the first hypothesis the natural mechanisms of loop migration would have been inhibited or blocked by the presence of bank protections under the second hypothesis a decrease in the frequency and or intensity of morphogenic hydrological events since the nineteenth century would have reduced the frequency of bedload mobilization and or reduced the capacity of the river to erode its banks to test these hypotheses the diachronic evolution of the planform was reconstituted at different time scales using a gis and field surveys morphological transformations were characterized and quantified eroded and vegetated areas length of eroded banks rates of bank retreat and the critical discharges of bedload mobilization and of lateral erosion were estimated engineering works in the riverbed were identified and when possible dated the results show that meander morphodynamics have been highly constrained and disrupted by engineering works probably for over a century however the meanders still have noticeable potential for bedload mobility and lateral erosion and hence for self restoration

large eruption triggered ocean island landslide at tenerife onshore record and long term effects on hazardous pyroclastic dispersal an extensive debris avalanche deposit has been discovered on canadas volcano tenerife canary islands the onshore component of the 733 3 ka abona landslide deposit exposes classic block facies and mixed facies across 90 km 2 three lines of evidence together show that the avalanche was triggered by an ignimbrite forming explosive eruption 1 the deposit is enclosed by phonolitic ignimbrites and is draped by a plinian fallout layer all within a single eruption unit 2 it contains prismatic jointed pumice blocks that were hot during landslide emplacement indicated by chilled rims and breadcrust surfaces 3 these blocks yield the same 40 ar 39 ar date as the associated ignimbrite and fall deposit landslide hummocks dammed surface water forming ephemeral lakes perched on the volcano flank phonolite dome growth destabilized the southeast sector of a mid pleistocene canadas caldera wall and created a major breach that affected the passage of destructive pyroclastic density currents on tenerife for 0 5 m y showing that landslides can have enduring consequences for pyroclastic dispersal and hazards

fingered flow the creator of sand columns in dune and beach sands sand columns sand cones sand mushrooms and other striking sand forms are frequently observed in the dutch and german beach and dune sands this paper aims to clarify the mechanism of sand column formation recently it has become evident that homogeneous beach and dune sands often become irregularly wetted by infiltrating rainwater in otherwise dry sandy soils wet preferential flow paths fingers may develop at two test sites the volumetric soil moisture content varied between 0 2 and 12 0 per cent the wet fingers represent the premature state of sand columns when the dry sand in between these fingers is blown away by the wind the more resistant wet sand of the fingers will remain in its place and appear as sand columns at the surface as a result of wind and erosive sand drifts striking sand forms may be formed

river channel adjustments downstream from channelization works in england and wales relatively little attention has been given to river channel adjustments that occur downstream from channelization works this study is concerned with the nature of channel adjustments downstream from a total of 46 channelization works located in low and high energy environments in england and wales channel changes are identified principally by the method of field survey and by reconstructing the original positions of eroded beds and banks use is also made of maps aerial photographs and engineering drawings of different dates and the technique of space for time substitution is applied enlargement of channel cross sections through erosion had occurred downstream from a variety of types sizes and dates of channelization works the maximum increase of channel size was 153 per cent out of a total of 14 sites with enlarged channel cross sections seven had undergone a change of width only at a further three width increased rather than depth and at the remaining four sites depth increases were dominant these sites all have relatively high stream powers factors causing spatial variation of erosion included tree roots locally binding bank sediments and the occurrence of bends planform change had taken place at only one site a further three high stream power sites had downstream reaches incised into bedrock and therefore did not exhibit adjustment channel enlargement is explained in terms of increased flood flows downstream from channelization works causing higher stream velocities which in turn cause erosion thereby increasing channel width and or depth examination of flow records for 35 stations revealed flood events which would formerly have spread overbank but are now confined by the channelization works and are therefore likely to alter downstream flows at sites with downstream change it is proposed that the energy of increased flows was sufficient to exceed a threshold required for erosion of perimeter sediments by contrast the absence of change at a majority of sites in low energy lowland areas could be a reflection of both the incompetence of increased flows to erode and resistance provided by perimeter sediments sites with erosion features appear not to have yet attained new equilibrium conditions

estimating the probability of river channel adjustment river channels respond not only to natural external controls and natural controls internal to individual drainage basins but also to the influence of human activity although many site specific instances of change have been documented the complexity of the process interactions means that very little is known about the general nature of different styles of adjustment or their relative sensitivity to drainage basin controls data obtained from the thames basin southeast england are used in a probabilistic approach to differentiate between four styles of river channel adjustment and a variety of drainage basin characteristics adopting a probabilistic approach quantifies the degree of confidence attributable to any prediction of river channel adjustment while acknowledging that certainties are difficult to obtain in studies of the natural environment this approach could thus allow environmental planning decisions to be made with a quantified degree of uncertainty four multivariate logistic regression models are described which use a combination of continuous and categorical variables to associate drainage basin characteristics with four styles of river channel adjustment derived from a reconnaissance evaluation survey in comparison it is shown that laterally migrating river channels are the most common natural channel type in the thames basin and their probability of occurrence rises to 71 per cent in sand gravel environments in channels regulated by low weirs deposition is the most likely channel activity where gradients are lower than 0 0040 whilst above this threshold the majority of channels are morphologically inactive in urban channels many of which are also lined by concrete the likelihood of obtaining a stable channel is mostly in excess of 80 per cent in channels straightened during this century deposition is most likely in gradients below 0 0050 whereas erosional enlargement is most probable above this value in channels which were initially channelized prior to this century deposition gives way to stability at a threshold gradient of 0 0080

on the formation of dissolution pipes in quaternary coastal calcareous arenites in mediterranean settings a large number of uniform cone shaped dissolution pipes has been observed and studied in quaternary coastal calcareous arenites in apulia and sardinia italy and tunisia these cylindrical tubes have a mean diameter of 52 8 cm and are up to 970 cm deep mean depth for sediment free pipes is 1 38 m they generally have smooth walls along their length are perfectly vertical and taper out towards their bottoms their development is not influenced by bedding nor fractures sometimes their walls are coated by a calcrete crust their morphology has been studied in detail and their relationships with the surrounding rocks and with the environment have been analysed the perfectly vertical development is a clear evidence of their genesis controlled by gravity the depth of the dissolution pipes can be described by an exponential distribution law the milanovic distribution strongly suggesting they developed by a diffusion mechanism from the surface vertically downward we believe dissolution pipes preferentially form in a covered karst setting local patches of soil and vegetation cause infiltration water to be enriched in carbon dioxide enhancing dissolution of carbonate cement and local small scale subsidence this process causes the formation of a depression cone that guides infiltrating waters towards these spots giving rise to the downward growth of gravity controlled dissolution pipes a change of climate from wetter phases to drier and hotter ones causes the formation of a calcrete lining fossilizing the pipes when the pipes become exposed to surface agents by erosion of the sediment cover or are laterally breached the loose quartz sand filling them may be transported elsewhere copyright 2010 john wiley sons ltd

stratigraphy structure and geochronology of the las canadas caldera tenerife canary islands after a long period of subaerial fissure fed extrusions of basaltic magmas 12 to 3 ma volcanic activity was then concentrated in the central part of tenerife phonolitic magma chambers formed and a central volcanic complex was constructed the las canadas edifice the formation of a large depression the las canadas caldera truncated the top of the edifice the active twin strato cones teide pico viejo are sited in this depression the history of the las canadas caldera and edifice are established from stratigraphy geochronology k ar dates and volcanological studies two different groups are recognized separated by a major unconformity the lower group is dated at 2 to 3 ma and includes the products of several volcanic centres which together represent several cycles the upper group ranges from 1 56 to 0 17 ma and includes three different formations representing three long term 100 to 300 ka volcanic cycles the periods of dormancy between each formation were of 120 to 250 ka duration the las canadas caldera is a multicyclic caldera which formed over the period 1 18 0 17 ma each cycle of activity represented by a formation culminated in caldera collapse which affected different sectors of the las canadas edifice geological observation and geochronology support an origin by collapse into a magma chamber the minimum volume of pyroclastic ejecta is substantially greater than the present caldera depression volume 45 km3 but approaches the inferred volume of the original caldera depression 140 km3 after the formation of the caldera sector collapses could also occur at the northern flank of the volcano causing the disappearance of the northern side of the caldera wall

coastal evolution on volcanic oceanic islands a complex interplay between volcanism erosion sedimentation sea level change and biogenic production abstract the growth and decay of oceanic hotspot volcanoes are intrinsically related to a competition between volcanic construction and erosive destruction and coastlines are at the forefront of such confrontation in this paper we review the several mechanisms that interact and contribute to the development of coastlines on oceanic island volcanoes and how these processes evolve throughout the islands lifetime volcanic constructional processes dominate during the emergent island and subaerial shield building stages during the emergent island stage surtseyan activity prevails and hydroclastic and pyroclastic structures form these structures are generally ephemeral because they can be rapidly obliterated by marine erosion with the onset of the subaerial shield building stage coastal evolution is essentially characterized by rapid but intermittent lateral growth through the formation of lava deltas largely expanding the coastlines until they typically reach their maximum extension with the post shield quiescence in volcanic activity destructive processes gradually take over and coastlines retreat adopting a more prominent profile mass wasting and marine and fluvial erosion reshape the landscape and if conditions are favorable biogenic processes assume a prominent role post erosional volcanic activity may temporarily reverse the balance by renewing coastline expansion but islands inexorably enter in a long battle for survival above sea level reef growth and or uplift may also prolong the island s lifetime above the waves the ultimate fate of most islands however is to be drowned through subsidence and or truncation by marine erosion

stable isotope composition of the carbonate concretion in loess and climate change carbonate concretions are commonly found in the loess in china oxygen and carbon isotopic compositions of carbonate concretions collected from 14 different paleosols s1 s14 in the lishi formation of luochuan loess section china were analysed the isotopic compositions of concretion in loess are useful tools in paleoclimatic study usually the more developed the paleosol is the less negative the 18o values and the more negative the 13c values are the oxygen isotopic composition of these paleosols varies within a range of about 1 3 the carbon isotopic composition however shows larger variations from one paleosol to the other within a range of 5 3 an attempt was made to semi quantitatively estimate the paleosol formation temperature and precipitation based on the carbon and oxygen isotopic data obtained

the morphology of the submarine flanks of volcanic ocean islands a comparative study of the canary and hawaiian hotspot islands the submarine flanks of volcanic islands are shaped by volcanic constructional processes landslides erosion sediment deposition and tectonic movements we use a newly acquired multibeam sonar dataset from the westerly canary islands el hierro la palma and tenerife to develop a comparison with the hawaiian islands which suggests differences in the processes constructing and modifying their flanks landslides affect the flanks of both island groups debris avalanches fast moving shallow landslides have left smooth chutes and blocky deposits in both cases but blocks within some hawaiian avalanche deposits are markedly larger we attribute the larger block sizes in the hawaiian islands to the fact that their avalanches were relatively unconfined whereas many canary and hawaiian avalanches with small block sizes appear to have been constrained down narrow chutes forcing interactions between blocks within the flows and encouraging disintegration furthermore the hawaiian avalanches with the largest blocks initiated near sea level whereas many of the canary avalanches initiated above sea level so hydraulic resistance of water entering cracks may be an additional factor in resisting block disintegration during flow slow moving deep seated slumps or volcanic spreading have produced submarine benches and tabular escarpments due to thrust faulting adjacent to several hawaiian rift zones but are not well developed in the canaries although volcanic morphology is partly obscured by sedimentation in the canaries we are able to interpret lava terraces around the deep flanks of el hierro which are similar to those found in the hawaiian islands however cones rather than terraces are the most common volcanic forms in the canary islands implying that flank eruptions have involved magma with significant volatile contents assuming that volatile contents dictate whether cones or terraces are formed these differences may ultimately originate from the different building rates of the two island groups for example the lack of evidence for high level magma chambers in the canaries associated with their lower outputs implies that there is less possibility for degassing of magma below the summit before lateral intrusion down rift zones hence cones rather than lava terraces are more commonly observed the apparent lack of slumping or volcano spreading could also reflect a lack of driving pressure from extensive high level magma chambers in the canaries

dimensionless morphological ratios versus stream power variations at bankfull stage in an ephemeral channel abstract dimensionless morphological ratios dmr generally are used in systemic proposals for stream classification and river restoration projects often such morphometric parameters including field data from channel cross sections develop into a template for a given geomorphic reference site in this study high resolution digital terrain models hrdtms combined with orthophotographs from 2018 and ground based surveys were used to analyze the spatial variability of dmr in a semi arid ephemeral stream subject to changes in stream power under bankfull conditions in particular a channel reach of 2 7 km in length along the upper mula stream in southeastern spain was chosen to test the relationships between the two types of variables rosgen s dmr width to depth ratio entrenchment ratio bank height ratio and hydraulic data at bankfull stage flow velocity froude number shear stress mean stream power and energy gradient among others were calculated by 1d hydrodynamic modeling and hrdtms prior entry of field information the resulting maps allowed comparison of stream power with dmr in relation to the channel stretch class and bed stability the results showed similar spatial patterns for the width to depth ratio and the bank height ratio the average values estimated in bend stretches were lower than along straight and slightly sinuous stretches and very similar to those of sub reaches from the inflection point to the meander bend apex however the entrenchment ratio followed a different pattern according to which the straight and slightly sinuous stretches were the most entrenched and the bend stretches presented a more moderate average entrenchment ratio in addition the energy balance and power gradient also experienced spatial variations in relation to the bed stability and dmr only in highly incised sub reaches were such relationships not significant the lack of a significant correlation between excess energy and bank height ratio or width to depth ratio over short lag distances was also verified regardless of the affected bedforms an anova showed important differences between the straight and slightly sinuous stretches and bend stretches which were strongly influenced by the incision and entrenchment ratios and the maximum bankfull depth

characterisation of a volcanic residual soil and its implications for large landslide phenomena application to tenerife canary islands large landslides are common processes during the evolution of volcanoes and individual events can exceed several cubic kilometres in volume volcanic slope failures are a significant risk for the neighbouring population due to their huge volumes and great runout distances around the canary archipelago a total of seventeen deposits of large landslides have been found and on tenerife seven large landslides have affected the subaerial and submarine morphology during the last 6 ma however the causes of such mass movements are still poorly understood this work analyses the events around the canary islands and focuses on the ones that occurred on tenerife in order to obtain new insights into the mechanisms of large volcanic landslides the study is divided into a first part that includes site investigations examining the general features favouring large scale failures at volcanoes the second part describes the laboratory tests used to analyse a residual soil that may be the potential slip surface of the slides on tenerife the site investigation revealed that regional tectonics and the climate have a significant influence on the spatial distribution of the landslides moreover morphological and geological features such as deep fluvial canyons a high coastal cliff and persistent dike intrusion may favour the initiation of slope failure a typical residual soil sample from the lateral scarp of the la orotava amphitheatre on tenerife was studied by carrying out standard laboratory tests the microstructure was analysed using environmental scanning electron microscopy and a particular bonding was found this bonding was also detected by the geotechnical tests consolidation tests and direct shear tests revealed that the mechanical behaviour of the residual soil changes greatly if the bonding of the soil is broken the bonded structure generally fails when the effective normal stress surpasses the yield strength of the bonding in the case of large volcanic landslides with thicknesses up to several hundred meters the high overburden easily exceeds this yield strength and generates a broken bonding therefore volcanic residual soils such as the one analysed in this study are perfect candidates for the potential failure surfaces of large volcanic landslides referring to the la orotava events we assume that residual soil layers and morphological geological and climatic features reduced the slope stability to critical conditions whereas a strong earthquake associated with a caldera collapse episode may have finally triggered the landslide the results obtained indicate that the residual soils play an important role in affecting the stability of volcano slopes and their destabilising influence significantly favours large scale sliding we suggest that the results obtained from this study can be applied to other locations since volcanic residual soils are common in volcanic areas

conceptual assessment of dis connectivity and its application to the ganga river dispersal system abstract connectivity in river dispersal systems is an important evolving concept and helps in understanding their dynamics in this study the types of connectivity have been defined on the basis of two components namely physical contact and transfer of material based on this four types of connectivity are recognized these are a active connected system b inactive connected system c partially active connected system and d disconnected system connectivity indices have been proposed based on the process understanding of different types of connectivity this conceptual understanding of connectivity has been applied to the ganga dispersal system a large river system results of the connectivity analysis on the ganga dispersal system reveal that different sets of data such as sediment budgets geochemical isotopic data and radiogenic 238 u 234 u 230 th data are noncoherent therefore developing rigorous and well constrained quantitative multidisciplinary data sets is needed to have a better understanding of connectivity at multiple spatio temporal scales in large river dispersal systems this would ultimately help model the dynamics of such systems

volcanic hazards from bezymianny and bandai type eruptions major slope failures are a significant degradational process at volcanoes slope failures and associated explosive eruptions have resulted in more than 20 000 fatalities in the past 400 years the historic record provides evidence for at least six of these events in the past century several historic debris avalanches exceed 1 km3 in volume holocene avalanches an order of magnitude larger have traveled 50 100 km from the source volcano and affected areas of 500 1500 km2 historic eruptions associated with major slope failures include those with a magmatic component bezymianny type and those solely phreatic bandai type the associated gravitational failures remove major segments of the volcanoes creating massive horseshoe shaped depressions commonly of caldera size the paroxysmal phase of a bezymianny type eruption may include powerful lateral explosions and pumiceous pyroclastic flows it is often followed by construction of lava dome or pyroclastic cone in the new crater bandai type eruptions begin and end with the paroxysmal phase during which slope failure removes a portion of the edifice massive volcanic landslides can also occur without related explosive eruptions as at the unzen volcano in 1792 the main potential hazards from these events derive from lateral blasts the debris avalanche itself and avalanche induced tsunamis lateral blasts produced by sudden decompression of hydrothermal and or magmatic systems can devastate areas in excess of 500km2 at velocities exceeding 100 m s 1 the ratio of area covered to distance traveled for the mount st helens and bezymianny lateral blasts exceeds that of many pyroclastic flows or surges of comparable volume the potential for large scale lateral blasts is likely related to the location of magma at the time of slope failure and appears highest when magma has intruded into the upper edifice as at mount st helens and bezymianny debris avalanches can move faster than 100 ms 1 and travel tens of kilometers when not confined by valley walls avalanches can affect wide areas beyond the volcano s flanks tsunamis from debris avalanches at coastal volcanoes have caused more fatalities than have the landslides themselves or associated eruptions the probable travel distance l of avalanches can be estimated by considering the potential vertical drop h data from a catalog of around 200 debris avalanches indicates that the h l rations for avalanches with volumes of 0 1 1 km3 average 0 13 and range 0 09 0 18 for avalanches exceeding 1 km3 h l ratios average 0 09 and range 0 5 0 13 large scale deformation of the volcanic edefice and intense local seismicity precede many slope failures and can indicate the likely failure direction and orientation of potential lateral blasts the nature and duration of precursory activity vary widely and the timing of slope faliure greatly affects the type of associated eruption bandai type eruptions are particularly difficult to anticipate because they typically climax suddenly without precursory eruptions and may be preceded by only short periods of seismicity