growth of a zoned plagioclase porphyroblast in a mylonite zoning patterns in a plagioclase porphyroblast in a blastomylonite derived from lewisian gneiss near loch eriboll northwest scotland suggest that the crystal grew during deformation discontinuities in the concentrations of cao k 2 o and feo mark the boundaries of overgrowths and define a core overgrowth structure the simultaneous changes in concentration of cao and k 2 o are used to construct a qualitative chemical potential diagram that reflects changes in a ca a 2 h and a k a h in the coexisting fluid during growth increases in these activity ratios are believed to have caused supersaturation of the grain boundary fluids with respect to plagioclase the repeated periods of growth indicate repeated overstepping of equilibrium which could have been caused by ion exchange on surfaces newly exposed during deformation these data fit a model that relates cyclic variations of strain rate in fault zones with cyclic periods of crystal growth which in turn could have a major influence on fault rock rheology

development of single crystal σ shaped quartz porphyroclasts by dissolution precipitation creep in a calcite marble shear zone abstract within a greenschist facies calcite marble shear zone isolated quartz grains change shape across the shear zone profile whereas quartz grains have a spherical to elongated shape in the coarse grained marble protolith and protomylonite they are asymmetric shaped porphyroclasts with wedge shaped appendages wings in ultramylonites in all cases quartz grains are single crystals they are sometimes twinned but never recrystallized stress induced dissolution precipitation creep is the favourable shape controlling process during deformation providing a relatively undeformed core truncation of pre existing cathodoluminescence cl patterns and syntaxial precipitation of wings the necessary fluids may have been released from fluid inclusions during dynamic recrystallization of the calcite matrix the development of shape is not related to the crystallographic orientation of the quartz porphyroclasts crystallographic orientation analysis by electron backscatter diffraction ebsd and cl analyses exclude crystal plasticity as a shape controlling mechanism of quartz grains during mylonitisation however in ultramylonites quartz clasts have a strong crystallographic preferred orientation cpo with c axes sub parallel to the shear direction this fabric is uncommon for quartz under greenschist facies conditions it might be explained by a strengthening of a pre existing weak cpo during mylonitisation by rigid particle rotation of elongated quartz grains

towards a protocol for laser scanning in fluvial geomorphology advances in spatial analytical software allow digital elevation models dems to be produced which accurately represent landform surface variability and offer an important opportunity to measure and monitor morphological change and sediment transfer across a variety of spatial scales many of the techniques presently employed aerial lidar edm theodolites gps photogrammetry suffer coverage or resolution limitations resulting in a trade off between spatial coverage and morphologic detail captured this issue is particularly important when rates of spatial and temporal change are considered for fluvial systems this paper describes the field and processing techniques required for oblique laser scanning to acquire 0 01 m resolution digital elevation data of an upland reach of the river wharfe in the uk the study site is variable with rapidly changing morphology diverse vegetation and the presence of water and these are evaluated with respect to laser data accuracy scan location frequency and distance are discussed with reference to survey accuracy and efficiency and a field protocol is proposed scan data cloud merging was achieved with a high degree of precision sub centimetre and positional data are shown to be very accurate for exposed surfaces vegetation and water decrease the accuracy as the laser pulse is often prevented from reaching the ground surface or is not returned copyright 2006 john wiley sons ltd

ground motion scaling in eastern sicily italy we describe the characteristics of crustal wave propagation in eastern sicily by using the background seismicity of the area we follow the approach de scribed by malagnini hermann and di bona 2000 and malagnini et al 2002 our data set consists of 106 earthquakes recorded by nine three component digital seismic stations between 1994 and 2001 we used only crustal events depths shal lower than 25 km with local magnitudes ranging from 1 0 to 4 3 and hypocentral distances from 10 to 130 km peak ground velocities from 1311 narrow bandpass filtered waveforms are mea sured in thefrequency range 1 0 16 0 hz and regressedtodefinecrustalpropagation excitation and site characteristics with respect to a reference station a subsequent modeling effort is carried out through the use of random vibration theory rvt for obtaining a quantitative evaluation of the apparent geometrical spreading g r and of the crustal quality factor q f an attenuation parameter j0 is also evaluated relative to a reference rock site the attenuation and source parameters estimated in this study are used through the rvt in order to predict the peak horizontal ground acceleration pga and the 5 damping pseudoacceleration spectra psa

evolution of mid channel bars in a braided river and complex response to reservoir construction an example from the middle hanjiang river china using the middle hanjiang river as an example this paper deals with the development of mid channel bars in a braided river as controlled by channel boundary conditions runoff and sediment load as well as reservoir construction relations have been established between indices describing the mid channel bars and the controlling variables such as the channel width the percentage silt clay content in the channel boundary and the energy expenditure of flowing water bank erosion provides space and material for mid channel bar formation so bank erosion rate can be closely related to mid channel bar indices the middle channel bars exhibit a complex evolutionary response to the reservoir regulated hydrological regime in the middle hanjiang river a descriptive model showing the complex response has been established 1997 john wiley sons ltd

a revision of the 1693 eastern sicily earthquake and tsunami the 1693 earthquake was a disastrous event affecting eastern sicily southern italy where it caused over 60 000 victims and total destruction of several villages and towns in the districts of siracusa ragusa and catania the earthquake was followed by a tsunami that struck the ionian coasts of sicily and the messina strait and was probably observed even in the aeolian islands historical documents on sea waves and flooding though not abundant allow us to form a picture of the tsunami first attack and inundation the first water movement all along the sicilian coastline was a strong sea withdrawal followed by a violent sea return and coastal flooding the main purpose of this research is to put constraints on the focal mechanism of this earthquake on the basis of the available documents on the tsunami 1 by simulating tsunami from different possible sources via numerical modeling based on finite element technique and shallow water approximation and 2 by choosing the source best fitting the tsunami data as the most plausible cause for this tsunami the relevance of this study should also be evaluated in light of the circumstance that no certain indication on the earthquake fault can be deduced from the available macroseismic data alone solving the source problem for this event one of the largest occurring in southeastern sicily in historical times is a significant contribution to understanding the seismotectonic regime of the region and to assessing the related earthquake and tsunami hazard risk with implications on mitigation policies

scour chain employment in gravel bed rivers abstract the dynamics of river beds can be assessed fromscour and fill data obtained from scour chains chains have not been used extensively in gravel bed rivers due to a variety of employment difficulties chain insertion anchoring and relocation can be determined with minimal manpower by utilising a set of tested employment methodologies these are decribed in sufficient detail to allow fluvial geomorphologists ecologists and river engineers to more commonly utilise chains in studies of river stability and river response

fluid rock reaction weakening of fault zones the presence of weak phyllosilicates may explain the low shear strengths of fault zones if they define well developed fabrics the growth of phyllosilicates is favored in meteoric water dominated granitic fault systems where mineral aqueous fluid equilibria predict that modal phyllosilicate will increase via feldspar replacement reactions in deeper more alkaline rock dominated regimes the reactions reverse and feldspars tend to replace phyllosilicates in mg rich mafic rocks however phyllosilicates chlorite biotite can replace stronger framework and chain silicates in both shallower approximately 10 km meteoric h sub 2 o dominated and in deeper alkaline rock dominated regimes where these phyllosilicates precipitate in active fault zones they contribute directly to reaction softening because low temperature deformation of phyllosilicates is not governed by frictional processes alone but can occur by pressure independent dislocation glide the strength of phyllosilicate rich fault rocks can be low at all depths low strain rate creep during interseismic periods can align phyllosilicate grains in foliated gouge and phyllonites where preferred orientations are strong and contiguity of phyllosilicates is large strengths of rocks within fault zones may approach minimum strengths defined by single phyllosilicate crystals fault zones containing localized high concentrations of phyllosilicates with strong preferred orientations in well defined folia can exhibit aseismic slip especially where mafic mg rich rocksmore occur along the fault like parts of the san andreas fault 104 refs 6 figs 1 tab less

the deep seismicity of the tyrrhenian sea summary l he study reappraises the deep seismicity of the tyrrhenian sea careful examination of the quality of reported hypocentres shows that the earthquakes define a zone dipping nw about 200 km along strike 50 km thick and reaching a depth of about 500 km the zone is slightly concave to the nw at a depth of 300 km but contrary to many previous reports is not tightly concave nor are there significant spatial gaps in the seismicity which is effectively continuous with depth seismicity is however concentrated in the depth interval 250 300 km where the dip of the seismic zone changes from 70 above 250 km to a more gentle dip of 45 at greater depths seven fault plane solutions are available for the largest earthquakes in this depth interval all of them consistent with a p axis down the dip of the seismic zone and all of them requiring movement on faults out of the plane of the subducting slab two deep earthquakes near naples lie well outside the main zone of activity for one of which a fault plane solution is available that has ap axis not aligned with the dip of the seismic zone the tightly concave slabgeometry favoured by other reports is supported mainly by the location of these events near naples which we think may represent deformation in a separate probably shallower dipping piece of subducted lithosphere the lack of shallow seismicity and particularly of thrust faulting earthquakes at the surface projection of the benioff zone suggests that active subduction has ceased estimates of the convergence rate responsible for subduction in the last 10 myr far exceed the present convergence rate of africa and eurasia suggesting that the subduction was related instead to the stretching and thinning of the crust in the tyrrhenian sea

a 550 km long moho traverse in the tyrrhenian sea from o b s recorded pn waves six obs deployed on a 550 km line in the tyrrhenian sea furnish reversed and overlapping profiles from 43 shots at 12 km intervals head waves recorded from a 8 km s refractor the moho permitted the computation of the crustal thickness which shows this basin to be underlain by an oceanic type of crust at least in two 100 km wide regions variations of pn arrival times mirror strong topographical changes of the moho differences in dips at the extremities towards corsica and calabria are documented

fluid enhanced deformation transformation of granitoids to banded mylonites western sierra nevada california and southeastern australia abstract deformation of tonalite and adamellite from the western sierra nevada california and southeastern australia has produced mylonite zones that show a broad range of microstructural development varying from strongly banded and or foliated to locally non foliated accompanying these fabrics are new mineral assemblages commonly rich in quartz and epidote whereas the banded foliated varieties appear to develop from progressive deformation of the granitic host they also occur in close proximity cm m to domains of non banded and or weakly to non foliated fabrics of similar mineralogy suggesting a complex timing and partitioning of deformation fluid flow and metamorphism in the mylonite zone whole rock major and trace element analyses of the tonalites show large enrichments of sio 2 cao fe 2 o 3 total fe and sr and strong depletions in na 2 o k 2 o feo mgo ba and rb with increasing stages of deformation although substantial chemical change appears to occur under static conditions locally chemical changes in the adamellite are much less dramatic all suites show systematic decrease in 18 o and convergence of oxygen isotopic compositions of whole rock and quartz with increasing deformation minimum fluid rock is estimated to lie between 0 1 and 10 increasing with intensity of deformation and depending on host composition isotopically exchanged seawater or connate water are the most plausible fluids chemical data from a number of mylonite zones in various orogenic belts show widely varying behavior gain loss of major and minor elements eleven factors control which and how much elements are gained lost during mylonitization of the granitoids the most influential of which are primary composition mineralogy and primary texture of the host as well as several aspects of fluid interaction active during deformation these influences may be a function of local rather than regional geological conditions

the lithosphere asthenosphere system in the calabrian arc and surrounding seas southern italy a fairly detailed structural model of the lithosphere asthenosphere system thickness s and p wave velocities of the crust and of the uppermost mantle layers has been defined in the calabrian arc region southern tyrrhenian sea calabria and the northwestern part of the ionian sea in southern italy using seismic data from literature as a priori constraints of the nonlinear inversion of surface wave data

dissolution and replacement creep a significant deformation mechanism in mid crustal rocks abstract zoning patterns and zoning truncations in metamorphic minerals in a granodioritic orthogneiss indicate that strain and s c fabrics in these rocks were produced by dissolution precipitation and replacement processes even at epidote amphibolite facies metamorphic conditions the metamorphic fabric is defined by alternating layers and folia dominated by quartz feldspars and biotite epidote zoning patterns in most metamorphic plagioclase orthoclase epidote and sphene are truncated at boundaries normal to the shortening direction suggesting dissolution interfaces of relict igneous orthoclase phenocrysts that face the shortening direction are embayed and replaced by biotite epidote and myrmekitic intergrowths of plagioclase and quartz metamorphic plagioclase grains are also replaced by epidote we interpret these microstructures to reflect strain enhanced dissolution the cores of many grains show asymmetric overgrowths with at least two generations of beards all oriented on the ends of grains that face the extension direction we interpret these textures to reflect precipitation of components dissolved by deformation enhanced dissolution while biotite and quartz probably deformed by dislocation creep the overall deformation was accommodated by dissolution perpendicular to the shortening direction and precipitation parallel to it these chemical processes must have been activated at lower stresses than the dislocation creep predicted from extrapolations of data from experiments in dry rocks thus wet crust is likely to be weaker than calculated from these experimental studies

direct dating of mylonite evolution a multi disciplinary geochronological study from the moine thrust zone nw scotland rb sr dating of sub closure temperature syn deformationly crystallized white micas from the moine mylonites knockan and dundonnell has yielded ages which vary from 437 ma to 408 ma morphological and major element analyses of the micas indicate that all the micas within the analysed samples were re crystallized during the moine thrust shearing the ages yielded are therefore interpreted as marking the end of crystal plastic deformation associated with shearing on the moine thrust the variation in ages between samples is significantly greater than the individual analytical errors and may be a product of strain localization within the shear zone alternatively it may indicate flow of strontium rich fluids derived from outside the shear zone implying that feldspars may act as potentially unreliable initial isotopic reservoirs even in very high strain samples within the greenschist facies shear zones however the rb sr age are internally consistent and compatible broadly with existing geological and geochronological data for the region suggesting that even if the feldspars have not acted as perfect initial isotopic reservoirs the resulting errors were minimal the general cessation of ductile deformation at c 430 ma probably dates the general initiation of imbrication within footwall to the moine thrust the age of 430 ma is therefore likely to be a time of significant brittle displacement on the underlying ben more thrust k ar dating of the re crystallized moine mylonite micas yielded anomalously old ages in comparison to rb sr values as a result of incorporation of excess ar during shearing the degree of incorporated excess ar decreases away from the base of the shear zone into the hanging wall becoming indiscernible at c 1 5 km structurally above the base of the shear zone the distance c 1 5 km may represent the distance that fluid can have flowed out of the shear zone during deformation

subduction zone geometry and stress patterns in the tyrrhenian sea joint hypocenter determination is performed for intermediate and deep earthquakes of the tyrrhenian sea region

the bed morphology of upland single thread channels in semi arid environments evidence of repeating bedforms and their wider implications for gravel bed rivers single thread gravel bed streams of moderate slope in the northern negev are characterized by three channel units bars exhibit steeper than average slopes and poorly sorted mixtures of small medium cobbles and coarse very coarse pebbles flats are associated with more gentle slopes and well sorted medium fine pebbles and granules and transitional units have intermediate slopes and grain size in general all three units are planar span the full channel width and have well defined boundaries bars and flats are more common than the transitional units and alternate downstream for distances of several hundred metres forming sequences that are reminiscent of the riffle pool structure commonly observed in humid temperate gravel bed rivers a notable contrast is the absence of significant bed relief bars lack crests and flats lack depressions the relative lack of bed relief in bar flat sequences is attributed to the high rate of sediment supply from the sparsely vegetated hillslopes which promotes the infilling of depressions and to the erosion of crests under conditions of intense transport this reduction of bed relief lowers channel roughness which in turn increases flow velocity and therefore the ability of the channel to transmit the large sediment loads it receives although our analyses pertain to a semi arid river system the results have wider implications for understanding the adjustment of channel bedform to high sediment loads in other fluvial environments copyright 2012 john wiley sons ltd

information on grain sizes in gravel bed rivers by automated image analysis abstract the time required in the field to characterize textural variation over gravel surfaces can be reduced by taking vertical photographs for subsequent image analysis we present modified edge detection algorithms which combine edge seeding with an image porosity concept and partial watershed segmentation the methods allow quick reliable and operator independent size analysis from a wide range of vertical bed surface images they are tested using 24 naturally lit images of an exposed river bed with mixed lithologies and partial burial of gravel by sand grain size percentiles derived by automated image analysis correlate closely with those from manual image analysis with only small and consistent degrees of bias they also correlate well with percentiles from field measurements with substantial bias which however is consistent so that it can be corrected for leaving a residual scatter of 0 25 where log2 mm over a wide range of bed conditions the bias depends somewhat on sand cover and the biggest residual discrepancies are for tail percentiles

on the mesozoic ionian basin summary new seismic reflection profiles of the italian deep crust project crop provide new insights on the structure of the ionian sea in spite of the apennines and hellenides neogene subduction zones two conjugate passive continental margins are preserved at the margins of the ionian sea along the malta escarpment to the southwest and the apulian escarpment to the northeast the ionian sea is likely to be a remnant of the mesozoic tethys ocean confined by these two conjugate passive continental margins the transition from continental to oceanic crust appears sharper to the northeast than to the southwest the basin between southeast sicily and southwest puglia was about 330 km wide and suggests a low spreading rate the inferred oceanic ridge should have been flattened by thermal cooling and buried by later sediments based on stratigraphic and structural constraints to the north in the apennines belt the ocean continued to the northwest this palaeogeography is supported by the seismicity of the apennines slab underneath the southern tyrrhenian sea which implies downgoing oceanic lithosphere the adjacent absence or paucity of deep seismicity does not imply absence of subduction but rather it can be interpreted as due to the more ductile behaviour of the subducted continental lithosphere surprisingly we note that where the oceanic inherited basin is subducting underneath the apennines in the hangingwall of the subduction hinge there are outcropping slices of continental crystalline basement previously deformed by the alpine orogen

the effect of dislocation density on the aqueous solubility of quartz and some geologic implications a theoretical approach the internal energy associated with dislocations is calculated in quartz as a function of dislocation density these calculations show that at dislocation densities of 109 1010 1011 and 1012 cm dislocation cm3 the energy stored per mole of quartz is 2 2 19 7 170 and 1426 j respectively the density of free dislocations in natural quartz rarely exceeds 109 line cm cm3 and the resulting increase in free energy is probably too small to affect any geochemical processes significantly this applies to the overwhelming volume of rocks in the earth s crust the density of dislocations in tangles may exceed 1011 line cm 2 which is significant but the volume of quartz containing tangles is a very small fraction of most quartz grains nevertheless where fluid rock ratios are low the aqueous activity of sio2 may be significantly increased by the dissolution of quartz containing dislocation tangles such dissolution could be geologically significant in active greenschist facies fault zones and mylonites where repeated cold working would produce a sustained source and large population of dislocation tangles in such a setting the locally high internal energies of quartz containing dislocation tangles would lead to strain solution the resulting high activity of aqueous silica would enhance the stability of feldspars and would establish chemical potential gradients of sio2 which would drive the diffusive mass transfer of sio2 out of the fault zone

evidence for deformation induced k feldspar replacement by myrmekite several examples of deformation induced myrmekite have been found in two amphibolite facies mylonites derived from granitic protoliths namely a muscovite poor s c mylonite and a single foliation muscovite poor mylonitic gneiss back scattered sem and conventional optical microscopy show that in both rock types syntectonic myrmekitic intergrowths of oligoclase and quartz formed on the two sides of k feldspar grains that faced the local inferred incremental shortening direction for the mylonite myrmekite does not occur on the two ends of the grain that faced the incremental stretching direction the replacement of k feldspar by plagioclase and quartz results in a volume decrease and is favoured on high normal stress sites around the grains we suggest that the ambient temperature pressure and chemical activities were such that the replacement reaction was favoured but the addition of extra strain energy along the high pressure sides of the grains localized the reaction at these sites this energy could arise from elastic strain or strain associated with tangled dislocations or twin boundaries the relative roles of stress and strain energy concentrations in driving the replacement reaction are not known but both were probably important

the non layering of gravel streambeds under ephemeral flood regimes abstract the two layer format common to perennial streambeds in which a relatively coarse armour overlies a finer subarmour develops as a function of both the ingress and subsequent near surface winnowing of interstitial material and the selective non entrainment or slower transport velocity of coarse clasts ephemeral streams appear to lack such vertical layering or are characterized by weak layer development some of this may be due to the degree of mixing associated with the scour and fill process however continuous monitoring of bedload discharge in the nahal yatir in the northern negev desert reveals that sediment transport rates are extremely high so that the chance of armour layer development through selective non entrainment is much reduced indeed a comparison of the bedload and bed material size distributions confirms a high degree of similarity and hints at equal mobility regardless of clast size the monitoring programme also indicates that the bed becomes highly mobile at comparatively modest fluid shear so that practically all floods are associated with high transport rates consequently the winnowing that might be brought about by low transport rate events does not occur even within a single event winnowing is precluded by the rapid nature of flow recession that is so characteristic of flash floods the high degree of bed material mobility is attributable in part to the lack of strength that would otherwise be a corollary of armour development however it also highlights the divergent nature of the feedback loops that govern the relationship between flow and channel deposit in ephemeral and perennial systems

red sedimentary units as indicators of early pleistocene tectonic activity in the southern negev desert israel abstract alluvial units termed red units accumulated along the western margin of the dead sea rift dsr valley southern negev desert israel in the early pleistocene these sedimentary units consist of coarse to fine grained alluvium of local origin which contain calcic paleosols the sediments of the red units accumulated in stream valleys and newly forming semi closed local tectonic basins during a tectonic phase that deformed the western margin of the dsr as a result of this deformation the pliocene northward flowing regional drainage system of the southern negev disintegrated to the present northeast flowing ephemeral drainage systems of nahal zihor nahal hiyyon and nahal paran all of them draining to the arava valley in the dsr this change was induced by two deformation episodes 1 reactivation of the zihor and the milhan faults two major northeast trending tectonic lines and 2 east and northeast tilting of the entire region during upwarp arching of the central negev the paleosols of the red units are characterized by pedogenic features such as rhizoconcretions and bk horizons the paleosols developed in the alluvial sediments that were deposited and preserved in local small structural basins along the main fault lines and in reversed or abandoned westward flowing pliocene stream valleys formation of paleosols was initiated in the stream valleys when they attained a near horizontal gradient due to gradual eastward directed regional tilting followed by low rates of deposition the sections of the red units in the pliocene valleys were incised due to continuing tilting which completely reversed the primary westward gradient of the valleys and they were incised by new east and northeast flowing streams the red units have paleoclimatic implications since the middle pleistocene the southern negev has been characterized by gypsic and salic soils typical of an extremely arid climate while the calcic soils detected in the red units point to a semi arid climate this indicates a gradual transition from more humid conditions in the early pleistocene to the present extreme aridity therefore the red units reflect a distinct tectonic and climatic regime and can serve as regional morphostratigraphic marker of early pleistocene age in this paper we used this marker to reconstruct the tectonic deformation that established the present configuration of the southern negev terrain

how do gravel bed rivers braid sedimentary processes and bed forms leading to the onset of braiding were observed in small scale hydraulic models of gravel bed streams the laboratory streams had a variety of combinations of constant discharge and slope but identical bed material particle size distributions from initially straight channels braiding occurred by four different processes deposition and accumulation of a central bar chute cutoff of point bars conversion of single transverse unit bars to mid channel braid bars and dissection of multiple bars in these experiments the chute cutoff mechanism was the most common but the predominant braiding mechanism depends upon sediment mobility excess bed shear stress and the bed form regime at very low excess bed shear stress the central bar process dominates but at higher excess bed shear stress slip face unit bars are more common bed scour at confluences is more pronounced and propogation of alternate convergence scour and divergence deposition is more likely thus chu

strain induced mineral growth in ductile shear zones and a preliminary study of ductile shearing in western newfoundland in the fleur de lys and the central gneiss terranes the presence of strain induced mineral growth characteristic of ductile shear zones within zones of rocks with mylonitic fabrics indicates the existence of major belts of layer parallel ductile shearing with complex evolutionary sequences kinematic markers in several of these shear belts indicate that shearing movements on initially probably gently inclined surfaces directed not normal to the axial trend of the orogen but parallel to it are tectonically important in western newfoundland the shear belts are in excess of 1 km thick and one well exposed example exhibits a pattern in which zones of the highest strain anastomose on the map scale the base of the fleur de lys supergroup is marked by one such major zone of shearing decollement in which kinematic indicators record movements directed to the north and to the south before the regional attitude of the rocks was steepened along the baie verte line earlier north and south directed movements

automatic grain sizing of vertical exposures of gravelly deposits abstract the grain size distribution gsd is a key indicator in stratigraphy and morphology it is a basic tool used by a variety of disciplines geology geomorphology archeology ecology and engineering automatic grain sizing ags has been developed to estimate the gsd of surfaces in a rapid and effortless manner yet the traditional bulk method time consuming and laborious is still in use for the determination of the gsd of coarse grained sedimentary deposits and of the near subsurface of landforms principally river beds the ags technique is examined here in its application to the stratigraphic record and to the subsurface images processed by ags and manual samples of coarse grained deposits in section were compared for evaluation of accuracy and determination of the extent of validation of the ags technique the ags often achieves results very similar to field counting especially when the largest grains are accounted for in the size of the sampling area and when photographs are taken afar without flash best results are provided when two images of the same sediment are taken at close range and also from afar to combine their gsds hence overcoming errors generated by resolution sampling area and grain size the computed errors are larger than those in prior studies yet remain reasonably small even though results are not bias corrected axes exposed in an outcrop very likely differ from those exposed on the surface and sediment properties and lighting conditions vary although results indicate a 25 burial effect the performance of the ags for sections is high unlike prior application of ags for riverbed surface openwork gravels conglomerate sections and the near subsurface include a matrix resulting in a somewhat larger mean irreducible error the technique may be utilized in studies of conglomerate texture allowing the evaluation of entire gsds under difficult sampling conditions an example use of ags to subsurface gsd evaluation is provided among others enabling an easy and fast method to calculate extent of armoring

the calabrian arc and the ionian sea in the dynamic evolution of the central mediterranean in the central mediterranean area it is possible to recognize three main realms the tyrrhenian sea the pelagian block and the ionian block these domains are limited by important fracture zones that are easily recognizable on land and offshore these fracture zones can be grouped into four main trends 1 the nw se trend which is characterized by dextral horizontal movements 2 the ne sw trend which is generally characterized by sinistral lateral horizontal movements 3 the e w trend which also shows dextral shear movements and 4 the n s trend which is characterized by normal faults only the tyrrhenian sea realm is characterized by a thinned crust of oceanic type and is connected to the apenninic chain by means of listric faults from a geophysical point of view the area shows a high heat flow which follows the main structural trends and positive gravimetric anomalies which are compatible with seismic refraction data and can be explained by the proposed model the pelagian block shows a continental crust about 20 km thick which progressively increases beneath the sicilian chain here an abrupt interruption with the tyrrhenian block takes place in the pelagian realm rifting processes developed according to the nw se and n s trend the n s trend characterizes the westernmost zone of the realm where volcanic processes and a relatively high heat flow can also be observed the ionian block is characterized by the following a thinned crust 17 20 km which increases 40 km towards the southern calabrian chain a thick sedimentary sequence high positive bouguer anomalies 300 mgal and very low heat flow 50 mw m 2 geophysical and structural analyses allowed us to evaluate the post tortonian evolution of the whole area under consideration this evolution resulted in continental crust formation according to a rigid plastic deformation model according to our model the ionian block can be considered as a domain characterized by a thinned continental crust and affected by intrusive material derived from the upper mantle furthermore this domain of probably jurassic age can be considered as a pelagic basin bordered by the pelagian block to the west and by the apulian block to the east northeast this basin according to its position with respect to the apenninic and sicilian chains has not been affected by tectogenesis and still represents a site of continuous sedimentation from a kinematic point of view the ionian realm can be linked with the pelagian block shifting towards the east northeast whereas it is limited towards the north by an e w fracture zone which regulates the opening of the tyrrhenian sea and the counterclockwise rotation of the apenninic chain according to the proposed model the opening of the tyrrhenian sea can be considered as a megaextension fracture which developed parallel to the maximum principal stress direction and evolved as a triangular shaped structural feature in preparing the model the authors have taken into account a large set of data collected both on land and offshore

evolution of the calabrian accretionary wedge central mediterranean 1 the neogene tectonics of the central mediterranean are related to the subduction and trench rollback of the ionian basin under eurasia causing the opening of the liguro provencal and tyrrhenian back arc basins and the formation of the calabrian accretionary wedge the calabrian accretionary wedge is a partially submerged accretionary complex located in the ionian offshore and laterally bounded by the apulia and malta escarpments while the history of the back arc extension process is fairly well defined the structure and evolution of the wedge are still poorly known we have analyzed and interpreted the available reflection multichannel and single channel seismic profiles in the ionian offshore and integrated them with other geological and geophysical data acquired in the last 40 years here we present unpublished seismic profiles to provide a new map of the tectonic structure of the ionian offshore and to define the structure of the wedge and its evolution during the last 15 myr our reconstruction points out that the messinian salinity crisis represents an important break in the evolution of the wedge as the basal decollement ramps up onto the messinian salt deposits producing a dramatic and fast forward propagation of the frontal thrust and resulting underplating of the underlying crustal ionian sequence during progressive trench rollback our results provide new insight into the style of accretion in a weakly converging setting which is typical for the mediterranean region

fluid rock interaction in some shear zones from the pyrenees mylonites from shear zones cutting hercynian gneisses in the central pyrenees have been studied in thin section and using the electron microprobe the shear zones contain retrogressive greenschist facies assemblages implying introduction of an aqueous fluid during deformation in the zones textural evidence suggests that fluid rock interaction occurred throughout the active life of the shear zones whole rock chemical changes during deformation are documented in a variety of mylonitic lithologies and retrogressed country rocks the overall effect was to reduce chemical differences between lithologies activity diagrams show that this would be expected if a hydrous fluid was circulating between different lithologies during deformation in most cases fluid rock ratios were relatively small resulting in gradual chemical changes and repeated recrystallization open system behaviour with reduction in the number of phases is seen in some granite mylonites suggesting focusing of fluid movement in parts of the shear zones continual fluid rock interaction may have led to reaction enhanced ductility in the shear zones over a long period of time the source of fluid is uncertain but may be related to underthrusting of material beneath the area investigated

effect of flood recession on scouring at bed sills the effect of the flood recession time on the local scour depth at bed sills in gravel deposits is examined experiments were carried out to study the development of scour holes under time varying hydraulic conditions with no upstream sediment feed triangular shaped hydrographs having recession times up to three times the duration of the rising limb were used traditionally the peak water discharge in any flood event is used as a design value in estimating the final depth of scour formed by a flood this approach is overly conservative when the flow hydrograph is steep i e during the occurrence of flash floods the actual reduction of the scour depth from this estimated value is dependent on both the characteristics of the flood event and the characteristics of the stream the results show that the maximum potential scour depth can be achieved only for hydrographs with long recession times while the rate of this process can be estimated as a function of the ratio between a characteristic flood time and the steady state temporal scale of scour development a method is proposed for the prediction of the scouring process under unsteady flows in terms of two dimensionless temporal parameters results obtained for clear water boundary conditions can be extended to sediment supply tests if specific supply input conditions hold

depositional character and preservation potential of coarse grained sediments deposited by flood events in hyper arid braided channels in the rift valley arava israel abstract four coarse grained braided channels undergoing rapid deposition in the hyper arid arava rift valley have been studied to determine the dynamics of strata deposition by monitored flood events and to ascertain the sedimentologic character of these event deposits the systems span granule sand to sandy gravel bed material having longitudinal bars with simultaneously increasing grains size slope and bed relief scour and fill were monitored along cross sections using scour chains and repeat surveys while event strata fill were described with reference to sediment calibre type of support grading thickness and location unlike many previous investigations of gravel sedimentology the source of information for this study involves not only stratigraphic description but also observation of the concomitant dynamics of the channel bed as expressed by the extent of event deposition the texture of the deposited sediment generally coarsens in sympathy with the surface bed texture of the studied channels the thickness of event deposited sediments increases as the magnitude of flow events increases the stratigraphic record is characterized by 1 sub parallel stratification 2 no grading 3 clast supported gravel infilled with sand granule matrices and 4 rapid sedimentation rates this character is hypothesized to mirror the elevated bedload fluxes in this hyper arid fluvial setting lacking densely vegetated banks the proximal braidplain of this arid environment often contains no extensive fine textured floodplain successions the depth of fill as well as the extent of strata obliteration increase with flood magnitude explaining the increased preservation potential of event strata with increase in flood magnitude it also explains why most event strata including large ones are only partially preserved

mineralogy geochemistry and the development of ductile shear zones in the grampian slide zone of the scottish central highlands the grampian slide zone comprises a system of shear zones characterized by strain induced syn tectonic muscovitization growth of porphyroblasts of plagioclase garnet and muscovite concordant quartz veinlets and by later tectonic sillimanite and late to post tectonic kyanite traverses across shear zones in the central highland division show progressive modification of original gneissic fabrics demonstrating that metamorphism and gneissification preceded the shearing event mylonitization involved bulk mobilization of alkalies na ca k and trace elements ba rb sr ni cr zr accompanied by decreasing fe oxidation ratios and increasing shearing progressively changed the mineral chemistry of reversely zoned plagioclase zoned garnet and micas advanced syn shearing blastesis produced a suite of lenticular pegmatitic segregation veinlets in the mylonites a coeval suite of larger intrusive pegmatites represents more mobile material that has migrated through the shear zones the pegmatites and the mylonite matrices yield u pb monazite ages of c 806 ma corresponding to the precambrian knoydartian event in the moine rocks of the northern highlands the shear zones record compressional transport directed towards the nne and in the northern sector of the central highlands were reactivated by later caledonian extensional se directed movement the presence of the c 806 ma event in the grampian group challenges recent proposals that early deformation across the entire dalradian supergroup can be correlated with the c 590 ma tay nappe

active fault kinematics and crustal stresses along the ionian margin of southeastern sicily since the late cretaceous onset of plate convergence between africa and europe the malta escarpment has been converted from a mesozoic passive margin into a mega hinge fault system with an additional sinistral strike slip component the modern tectonic stress regime with nw se directed maximum horizontal stresses has been established since late messinian times since the pleistocene sinistral strike slip deformation and contemporaneous normal faulting along the malta escarpment have induced the opening of oblique trending onshore grabens at the eastern margin of the hyblean plateau in this study we focus on the kinematics the controlling state of stress and the temporal variation of the neotectonic to active strike slip and normal fault structures the stress tensor calculations reveals that the widespread map scaled to meso scaled normal fault structures are governed by the long term extensional state of stress during the quaternary this long term stress tensor is predominantly controlled by gravitational induced stresses due to vertical load 1 sv and lateral extension due to the topographic gradient of the malta escarpment 3 sh ne sw in this case the average tectonic stresses 2 sh nw se transmitted by the regional to plate tectonic stress field are significantly smaller than the gravitational induced stresses in contrast the clear localization of conjugate sets of meso scaled strike slip fault structures and shear zones without accompanying normal fault structures give strong indications for episodic seismotectonic strike slip faulting under critical stress conditions in this state tectonically induced maximum horizontal stresses are successively increased by ongoing plate convergence from low level stress magnitudes 1 sv 2 sh nw se up to critical stress magnitudes 1 sh nw se 2 sv which are significantly larger than gravitational stresses at the critical state seismotectonic stress release occurs by active strike slip faulting as recently indicated in mid crustal levels by the moderate 1990 augusta earthquake and re establishes the long term extensional state of stress because the strike slip faults and shear zones in the study area were formed as surface ruptures they additionally give indications of episodic large earthquakes in this region with magnitudes greater than 6 0 as reported by several large earthquakes devastating e and se sicily in historical times

measurements in a braided river chute and lobe 2 sorting of bed load during entrainment transport and deposition grain size distributions of bed material bed load and bar head deposition were sampled during the evolution of a chute and lobe in the braided gravel bed sunwapta river alberta although bed shear stress and total bed load transport rate varied substantially within the reach and from day to day ferguson et al this issue the median diameter d50 of bed load was remarkably constant the bed initially fined from chute to bar head but became more uniform sediment deposited on the bar head also had a near constant d50 similar to that of the bed load truncated at the same lower size limit both load and deposition were finer on average than the bed suggesting overall selective transport despite little sign of local sorting in contrast to median diameters maximum sizes dmax of sediment in motion and deposited on the bar head varied substantially and showed a weak but significant dependence on shear stress inferring selective entrainment from this evidence alone would be dubious because dmax was also found to increase systematically with the mass of sediment sampled however two different methods of analysis of fractional transport rates throughout the size range also showed size selective entrainment and transport in the marginal transport conditions of this study size sorting appears to occur but only weakly and mainly in the coarser fractions

morphotextural characterization of dryland braided channels braided streams have been extensively studied in humid environments or in flumes that simulate them dryland rivers have bare catchments rapid recession hydrographs and unarmored beds resulting in high bed load discharges our objective was to characterize the morphotexture of the morphological elements bar anabranches chutes and confluences in a dryland braided system morphological elements measured in wadis ze elim rahaf and roded located in southeast israel were scanned using terrestrial laser scanning from which digital elevation models were generated roughness was evaluated from the standard deviation of detrended surfaces or from wolman sampled surface texture armoring of the bar and the adjacent anabranch was also evaluated scour chains were deployed in confluences to measure scour and fill during flow events dryland anabranches were finer grained and less armored than the adjacent bars bed load deposited as midchannel bars or on top of existing bars and thus associated with the depositional braiding process was enriched by the coarser fractions while the remaining bed load was deposited in the anabranches during the rapid flow recession chutes associated with erosional braiding processes were formed as topographic features with high local gradients enabling winnowing of fines deposited immediately downstream or transported further away scour chains inserted in the confluence zones demonstrated the formation and obliteration of a scour hole during a flow event the terrestrial laser scanning based digital elevation models and roughness analyses suggest that the hydrological regime of ephemeral channels with short lived recessions is responsible for the morphotextural setting of braid systems in arid environments

plio quaternary tectonic evolution and structure of the catania foredeep the northern hyblean plateau and the ionian shelf se sicily abstract available multi and single channel seismic reflection profiles calibrated by onshore borehole data have been used for defining the structural styles in the shelf and slope of the ionian sea between catania and augusta se sicily the geological and geophysical data suggest that this area represents a segment of the foredeep foreland system which collapsed after late pliocene times the foundering was controlled by normal faults trending ne sw which flank the southern margin of the catania foredeep onland in outcrop these faults appear largely to be post dated by lower pleistocene sediments nearshore carbonates passing laterally into basinal clays which lie unconformably upon older substrata offshore close to the southern edge of the foredeep seismic lines allow recognition of two distinct units a syn rift wedge upper pliocene submarine tholeiites and sediments and a post rift sequence which can be correlated with lower pleistocene carbonates sands and clays recognisable on land both in outcrop and by borehole data the true frontal part of the thrust belt as detected by the seismic lines occupies the inner part of the area investigated and is buried by upper pliocene and lower pleistocene sediments however the compressive deformation seems to propagate toward the south southeast by means of growing detachment levels developing at depth within pleistocene marine clays for a length of about 10 km ahead of the present day thrust front offshore the faults trending ne sw are dissected towards the east by faults trending nnw sse subparallel to the malta escarpment which flank the edge of the submerged messina rise these faults originating in a steep scarp which drops eastwards to the deep ionian basin have triggered submarine slides and affected the present day seafloor sediments as shown by seismic lines and as stressed by the modern seismicity of the area some of the faults along the malta escarpment could be still active

ionian basin and calabria arc some new elements from dss data abstract the interpretation of results from a 250 km long seismic refraction traverse recorded using ocean bottom seismometers in the northwestern ionian sea and a fan profile recorded across southern calabria have augmented previous studies by placing additional constraints on the tyrrhenian sea calabria ionian sea transition overlapping branches of pn phases confirm the existence of a thinned crust about 13 km giving rise to the major bouguer anomaly high of the central ionian basin a low average crustal velocity is observed throughout the basin in accordance with the very thick sedimentary cover exemplified by previous seismic surveys a deepening moho may be followed continuously from the centre of the basin to 40 km offshore from calabria where a sudden depth decrease 30 to 20 km is accompanied by a sharp change in the crustal velocity structure the estimated depth of such a shallower moho towards the northwest confirmed by a shot recorded in a fan geometry across southern calabria is in accordance with that found earlier for the southernmost margin of the tyrrhenian basin

two stage growth of the calabrian accretionary wedge in the ionian sea central mediterranean constraints from depth migrated multichannel seismic data new structural images of the calabrian accretionary wedge are presented from depth migrated multichannel seismic data a combined interpretation swath mapping bathymetry allows us to identify five morphological domains on the basis of their tectonic style 1 beneath the undeformed abyssal plain a set of deep nw vergent reverse faults cuts the ionian oceanic crust and thick pre messinian sediments 2 towards the nw the low taper post messinian wedge overlying a shallow nw dipping decollement at the base of the messinian evaporites and exhibiting strong tectonic thickening 3 beneath the flat central transition zone a backthrust marks the contact between the post and pre messinian wedges here the decollement dip increases 3 cutting through deeper sediments to reach 10 km depth 4 beneath the pre messinian calabrian wedge some steep landward dipping features are imaged where underplating may occur 5 beneath the inner plateau a fore arc basin lies above the top of the calabrian continental basement imaged at 8 km depth the architecture of the calabrian accretionary complex is very similar to the mediterranean ridge both systems consist of a an external low taper post messinian wedge overlying a thick undeformed section of underthrust mesozoic sediments and b an internal pre messinian wedge where the decollement steps down and where the underthrust section is presumably underplated we perform area balancing and show that since the messinian the calabrian accretionary wedge has undergone extremely rapid outward growth at an average rate of 30 km ma which makes it the fastest growing accretionary wedge over the past 5 ma highlights relation between the pre and post messinian juxtaposed wedges contact between these wedges along a major backthrust the 130 km long outer calabrian prism a huge salt bearing body one of the fastest growing wedges 2 0 cm year in recent earth history 170 km amount of post messinian subduction subduction rate 3 4 cm year

measurements in a braided river chute and lobe 1 flow pattern sediment transport and channel change this paper and its companion ashworth et al this issue discuss measurements of channel change and associated flow and sediment transport processes in a representative chute and bar reach within a proglacial gravel bed river the sunwapta river in the canadian rockies during a week in which water discharge through the reach increased then decreased a sediment wave passed into and partly along the reach at first the chute aggraded then sediment was eroded from the chute and deposited in a prograding lobe to one side of the original bar head between two distributaries measurements of velocity shear stress and gravel transport rate revealed day to day changes in the divergent pattern of flow and sediment transport the off center location of the lobe reflected an initial asymmetry in the pattern of flow and sediment transport but as the lobe grew the flow and transport gradually switched away to the other distributary width averaged bed load transport rates do not agree well with average rates inferred from bar head deposition or from volumes and spatial patterns of scour and fill the indirect estimates are considered more reliable than those based on direct sampling for necessarily brief durations by the end of the study the new lobe had almost accreted onto the original bar head supporting the idea that most braid bars are of compound origin temporal and spatial patterns in grain size distributions of the bed bed load and deposited sediment are discussed in the companion paper

lithostratigraphic correlation of blaini formation late proterozoic lesser himalaya india with other late proterozoic tillite sequences the blaini formation of the lesser himalaya has long been considered permo carboniferous in age on simple lithological correlation with gondwana tillites in southern india rare and non repeatable finds of fossils from the type area were thought to confirm this recently lower cambrian faunas have been recorded from the overlying tal and krol formations and possible metazoan trails recorded from the blaini itself in addition the blaini formation is even on a lithostratigraphic comparison much more like other late proterozoic glacial sequences the term blaini formation should only be used for rocks of the type area not for widely scattered glacial deposits which may or may not be correlatable with the type section the persistent belief in the paleozoic age of the blaini and adjacent formations has for long retarded unterstanding of lesser himalaya stratigraphy and tectonics

two ship deep seismic soundings in the basins of the eastern mediterranean sea pasiphae cruise summary new results from a two ship refraction and oblique reflection deep seismic cruise are presented to discuss the nature of the crust in the ionian sirte and herodotus abyssal plains these expanding spread profiles were processed and analysed in both the x t and p domains arrival times of reflected and refracted branches are matched by ray tracing in both domains in spite of a shallow evaporitic sequence messinian evaporites deposited on top of a thick sedimentary pile responsible for velocity inversions on many profiles we obtain excellent velocity control down to moho depth pmp and pn 8 4 8 6 km s 1 arrivals are observed the three basins have a relatively thin crust 8 to 11 km overlain by a thick sedimentary cover up to 10km in the herodotus abyssal plain the moho boundary and main crustal units identified in the basins can be followed beneath the calabrian prism to the west and beneath the mediterranean ridge to the east the crustal structure is of oceanic type for both the ionian and sirte basins where typical oceanic layer 2 and 3 are recognized the thin crust of the herodotus basin may be interpreted either as oceanic or thinned continental crust about 10 km thick the top of the crust of the herodotus basin is much deeper therefore the herodotus basin is probably significantly older than the ionian basin triassic versus early cretaceous in age

crustal image of the ionian basin and its calabrian margins abstract previous seismic investigation of the crustal structure in the ionian basin has been limited to shallow penetration seismics of the 1970 s characterized by inadequate source power and low fold earlier obs and esp seismic refraction experiments have not been able to firmly resolve one of the principal scientific problems for this region which is whether the ionian basin is floored by oceanic crust or by highly attenuated continental crust a second elusive problem is the nature of the transition of the boundaries between the ionian basin and its margins in this paper we describe and interpret new deep seismic reflection and wide angle data collected in the western ionian sea and the calabria region of italy one of the principal features of our multichannel reflection data beneath the ionian basin is a band of layered high amplitude reflections near the base of the crust this band shows a quasi monochromatic ca 8 to 10 hz frequency and a traveltime thickness of 1 to 1 5 s these images contrast with the well known reflection patterns of mesozoic oceanic crust investigated in the atlantic ocean there is evidence that the low frequency band dips down towards the edge of the malta escarpment me where landward dipping reflectors separate continental and intermediate type crust in the central tract of the me the increased traveltimes of the lower crustal reflectors and moho from the basin towards the southern and eastern margins of southern calabria could be partially due to the velocity pull down effect of the sedimentary pile of the arc although a true dip of 15 to 18 over 60 km distance can be substantiated moreover the reflecting band maintains its reflectivity and thickness until its abrupt termination beneath the ionian continuation of the calabrian compressional crustal structures the coincident acquisition of wide angle seismic data and marine reflection seismic data provided a landward extension of the survey which will complement existing geologic information on the deep framework of the ionian basin and its calabrian margin

in situ characterization of grain scale fluvial morphology using terrestrial laser scanning the grain scale morphology of fluvial sediments is an important control on the character and dynamics of river systems however current understanding of its role is limited by the difficulties of robustly quantifying field surface morphology terrestrial laser scanning tls offers a new methodology for the rapid acquisition of high resolution and high precision surface elevation data from in situ sediments to date most environmental and fluvial applications of tls have focused on large scale systems capturing macroscale morphologies application of this new technology at scales necessary to characterize the complexity of grain scale fluvial sediments therefore requires a robust assessment of the quality and sources of errors in close range tls data this paper describes both laboratory and field experiments designed to evaluate close range tls for sedimentological applications and to develop protocols for data acquisition in the former controlled experiments comprising high resolution scans of white grey and black planes and a sphere were used to quantify the magnitude and source of three dimensional 3d point errors resulting from a combination of surface geometry reflectivity effects and inherent instrument precision subsequently a methodology for the collection and processing of grain scale tls data is described through an application to a coarse grained gravel system the river feshie d50 32 to 63 mm this stepwise strategy incorporates averaging repeat scans and filtering scan artefact and non surface points using local 3d search algorithms the sensitivity of the results to the filter parameter values are assessed by careful internal validation of digital terrain models dtms created from the resulting point cloud data the transferability of this methodology is assessed through application to a second river bury green brook dominated by finer gravel d50 18 to 33 mm the factor limiting the resolution of dtms created from this second dataset was found to be the relative sizes of the laser footprint and smallest grains copyright 2009 john wiley sons ltd

syntectonic porphyroblast growth in phyllites textures and processes porphyroblast textures in a karakorum phyllite reveal that porphyroblast growth was syn tectonic with respect to a cleavage forming deformation during and after porphyroblast growth it partitions the deformation such that zones of intensified cleavage are developed which wrap around the porphyroblast whilst the porphyroblast and its strain shadow undergo little deformation porphyroblast strain shadows comprise quartz calcite and felspar with little mica and are probably formed by solution transfer during deformation unless the deformation is so strongly partitioned that no deformation of the porphyroblasts and their immediate surrounds occurs inequidimensional porphyroblasts will rotate porphyroblasts undergo some dissolution after they have finished growing

rotation of porphyroblasts in non coaxial deformation insights from computer simulations porphyroblast inclusion trails have the potential to provide critical information about tectonometamorphic events recently however traditional interpretations of inclusion trails have been called into question by the suggestions that porphyroblasts do not rotate during non coaxial deformation and that apparent spiral inclusion trails can be generated in coaxial deformation we present a new computer model that simulates inclusion trail development model results suggest 1 that the extent of porphyroblast rotation is controlled by conditions at the porphyroblast matrix boundary 2 that curved inclusion trails may develop in unrotated porphyroblasts 3 that classic snowball inclusion trails are most simply explained by rotational growth histories and 4 that some of the observations used to support the view that porphyroblasts do not rotate e g weakly sigmoidal inclusion trails apparent truncations of inclusion trails can be accounted for by variations in the growth rate of rotating porphyroblasts

sediment transport and bed morphology at river channel confluences river channel confluences form important morphological elements of every river system being points at which rapid changes in flow sediment discharge and hydraulic geometry must be accommodated this article presents results of a quantitative investigation of sediment transport at channel confluences accomplished through both scaled laboratory flume simulation and complementary monitoring of a natural channel confluence bed morphology at channel confluences is characterized by three distinct elements avalanche faces at the mouth of each confluent channel a deep central scour and a bar within the separation zone formed at the downstream junction corner these elements are controlled predominantly by the confluence angle and the ratio of discharges between the tributary and mainstream channels as confluence angle and discharge ratio increase the sediment contributions from the confluent channels are progressively segregated in their paths through the junction with sediment being transported around rather than through the centre of the confluence this segregation of sediment loads is accompanied by the retreat of the main channel avalanche face from the confluence an increase in the scour depth a change in the orientation of the scour and an increase in the size of the separation zone bar field measurements closely replicate the flume simulation a model of sediment transport and bed morphology links these features to the fluid dynamics of these sites an understanding of confluence dynamics is important not only in considerations of channel morphology and design criteria but must form the basis for the interpretation of confluence sediments in the ancient record

iron coating in recent terrace sequences under extremely arid conditions summary precise documentation of ferric oxide coating on calcareous sands of 13 15 recent alluvial fan terraces in the dead sea area israel indicates a gradual ferric enrichment over the last 12 00 years airborne dust is suggested as the main source the staining on the low terraces indicates that coating during short increments of time than hitherto generally accepted up to periods of a few tenths of years is distinguishable in an extremely arid environment the results suggest an initial stage of alluvial red bed formation

a seismic reflection refraction experiment across the exposed lower crust in calabria southern italy first results exposed crystalline basement of the serre mountains in calabria presents a tilted block of a nearly complete section of the hercynian continental lower crust hclc in addition to petrological and structural data from surface mapping and petrophysical data from the laboratory a seismic reflection refraction experiment was conducted in may 1990 this consisted of a 40 km long n s profile crossing the hclc and of four short transverse profiles each recorded using 3 component receivers with an 80 m spacing and explosive sources the reflectivity of the outcropping lower crustal units is lower than theoretically predicted from the observed compositional layering a low velocity zone outcropping in the north and dipping to the south marks the contact between the hclc and the underlying alpine metamorphic units below this zone the deeper crust appears well structured by strong and continuous discrete reflections down to 6 5 8 s t w t presumably the crust mantle boundary at 19 24 km depth with a dominant dip toward the south analysis of refracted wave velocities reveals values systematically lower by up to 30 than laboratory data on rock samples or calculated data from modal analysis this discrepancy can only partly be explained by the effect of microcracks 10 the underestimation of the amount of leucosomes 2 5 and the effect of seismic anisotropy 0 5 the remaining discrepancy must be attributed to large scale alteration of the rocks due to apennine tectogenetic events

modeling river bed morphology roughness and surface sedimentology using high resolution terrestrial laser scanning 1 recent advances in technology have revolutionized the acquisition of topographic data offering new perspectives on the structure and morphology of the earth s surface these developments have had a profound impact on the practice of river science creating a step change in the dimensionality resolution and precision of fluvial terrain models the emergence of hyperscale survey methods including structure from motion photogrammetry and terrestrial laser scanning tls now presents the opportunity to acquire 3 d point cloud data that capture grain scale detail over reach scale extents translating these data into geomorphologically relevant products is however not straightforward unlike traditional survey methods tls acquires observations rapidly and automatically but unselectively this results in considerable noise associated with backscatter from vegetation and other artifacts moreover the large data volumes are difficult to visualize require very high capacity storage and are not incorporated readily into gis and simulation models in this paper we analyze the geomorphological integrity of multiscale terrain models rendered from a tls survey of the braided river feshie scotland these raster terrain models are generated using a new computationally efficient geospatial toolkit the topographic point cloud analysis toolkit topcat this performs an intelligent decimation of point cloud data into a set of 2 5 d terrain models that retain information on the high frequency subgrid topography as the moments of the locally detrended elevation distribution the results quantify the degree of terrain generalization inherent in conventional fluvial dems and illustrate how subgrid topographic statistics can be used to map the spatial pattern of particle size grain roughness and sedimentary facies at the reach scale

dynamic single thread channels maintained by the interaction of flow and vegetation most rivers on earth today flow as a single channel in some cases with occasional islands and follow a more or less sinuous course however single thread channels have proven difficult to reproduce and study experimentally experimental self formed channels tend to widen and subdivide leading to a braided pattern cohesive sediment has been the main mechanism studied for stabilizing banks and producing a single thread channel we show how laboratory experiments using vegetation to stabilize banks can organize the flow and convert the planform morphology from braided to single thread our experimental strategy a repeated cycle of short periods of high water discharge alternating with longer periods of low discharge accompanied by plant seeding and growth leads to the evolution of a dynamic self maintaining single thread channel with well defined banks and floodplain by eliminating weak flow paths the vegetation corrals the water into a single dominant channel until the reduction in total wetted width leads to a new self organized state in which the flow removes vegetated area as fast as it is produced the new channel is deeper and has a broader distribution of depths than the braided one with channel size adjusted to carry almost all the flood flow the resulting system maintains a dynamic steady state via similar mechanisms to those that operate in meandering channels in the field specifically erosion at the outside of bends bend growth and bar development our methodology provides a basis for experimental development of self sustaining high amplitude meanders and has applications for river management and basic research purposes

downstream changes in dryland river channels the northern plains of arid central australia abstract many dryland rivers undergo marked downstream changes owing to factors such as infrequent floods flow transmission losses and typically few tributary inflows beyond the headwaters along the sandover bundey sandover bundey and woodforde rivers on the northern plains of arid central australia downstream channel changes are broadly similar in upland zones small rocky channels transporting sand and gravel gradually increase in size before entering piedmont zones where channels and narrow floodplains are confined by bedrock alluvial terraces or aeolian dunes in lower gradient lowland zones channels and floodplains remain confined and in the absence of tributary inflows channel cross sectional areas and discharges decrease downstream confining landforms are not present in floodout zones which results in splay formation increased floodplain widths and marked overall downstream decreases in cross sectional areas eventually channelised flow and bedload transport terminate although occasional large floods continue across extensive unchanneled alluvial surfaces termed floodouts these broad similarities apart downstream changes along the three rivers differ in detail the sandover is largely a single thread channel whereas many reaches of the sandover bundey and woodforde are anabranched on the small woodforde river downstream decreases in parameters such as cross sectional area and width are roughly linear on the larger sandover and sandover bundey downstream changes are more irregular particularly through the floodout zones where there are marked fluctuations in widths depths and bed slopes the irregular downstream changes typical of the lower reaches of these large rivers may be due to the reduced influence of vegetation on bankline stability and width adjustment relative to that of smaller rivers on the northern plains as in other drylands complex interactions between discharge sediment transport slope patterns of tributary drainage bank sediment type and vegetation result in variable patterns of downstream channel change