channel arrangements and depositional styles in the sao lourenco fluvial megafan brazilian pantanal wetland abstract the brazilian pantanal is an extensive lowland tropical basin characterized by the presence of fluvial megafans and seasonally inundated savanna floodplain wetlands with an area of about 16 000 km 2 the sao lourenco is the second largest megafan in the pantanal three distinct fluvial channel styles that formed at different times during the late quaternary are found here a geomorphological and sedimentary assessment of these depositional patterns provides valuable insight on the environmental context of their evolution new optically stimulated luminescence data indicate that the upper five meters of sediment in the sao lourenco megafan has been accumulating since the late pleistocene ancient fan lobes located in upper and intermediate fan settings consist of medium and coarse grained fluvial sands and exhibit well preserved distributary braided paleochannels on their surfaces as the megafan evolved through time pleistocene lobes were incised by a prominent valley filled with holocene aged meander belt deposits which consist of silts interbedded with very fine sands and clays currently the incised valley is a zone of sediment bypass modern deposition occurs along the distal toe of the megafan system where lobes characterized by distributary channel levee ridges are widespread these features formed by progradation of avulsion belts into a broad swampy floodbasin which caused the lower portion of the meander belt to be abandoned the significant differences observed in intra fan morphology appear to be linked to the variability in effective precipitation fan lobes deposited with braided distributary channels occurred under relatively dry conditions in the late pleistocene by contrast aggradational meander belt deposits and lobes with distributary channel levee ridges formed during fluctuating precipitation conditions of the holocene when the pantanal emerged from deglacial aridity modern lobes form under heavy seasonal flooding and deposition occurs in response to very rapid and common avulsion events these results have implications for interpreting the complexity of megafan facies in similar continental basins

tectonics and slumping in the source region of the 1998 papua new guinea tsunami from seismic reflection images in september 1999 we collected seven high resolution seismic reflection profiles along the northern continental margin of papua new guinea which targeted the source region of the 1998 tsunami that inundated sissano lagoon we utilized swath bathymetry collected by the jamstec sopac groups in january 1999 the seismic profiles image several faults bottom simulating reflectors and a large rotational slump the slump has a head scarp of 100 m vertical extent coinciding with the headwall and tension cracks observed previously by submersible at the southern edge of the amphitheater the central back rotated part of the slump is coherent with parallel reflections the interpreted basal failure plane has a maximum depth of 760 m below the seafloor and it crops out at a steep escarpment about 100 meters high located 4 5 km north of the head scarp this escarpment separates the slide toe from a series of seafloor parallel coherent reflections that are top lapped by basin deposits at the foot of the amphitheater to the north the cross sectional area of the displaced mass is 2 3 km2 from the bathymetry the width is approximately 2 5 3 km yielding a total volume assuming parabolic shape of 3 8 4 6 km3 based on these interpretations the slump was restored to its undeformed position this technique yields a center of mass vertical drop of 380 m horizontal movement of 840 m and slip of 980 m along the slide plane

low sinuosity and meandering bedload rivers of the okavango fan channel confinement by vegetated levees without fine sediment abstract the river systems of the okavango fan negate present fluviological perceptions that fluvial geometry is primarily dependent upon the type of sediment load being carried by the river in northwest botswana meandering and low sinuosity rivers both of which may show anastomosis are distinctly bedload in character this is mainly because of a restricted source of clastic sediment consisting of aeolian sand from the tertiary to recent kalahari basin all that seems to be required therefore to control low sinuosity and meandering geometries is adequate confinement of channels in the study examples this is provided by heavily vegetated levees comprising peat formed from and colonised by a cyperus papyrus dominated flora fine sediment plays almost no role in the confinement process active and abandoned examples of low sinuosity river channels were studied an inversion of topography develops in the latter caused by the low survival probability of metres thick peat levees desiccation and burning of peat ultimately form a degraded ash layer only tens of centimetres thick the channel sand then stands as a ridge rising above the surrounding fan surface in both examples studied no crevasse splays occur but hippopotami trails breach the levees to form minor distributary channels which become filled with sand the sand ultimately grades backwards to plug the breach meander belts are also developed particularly in the upper fan and entry corridor cut banks incise into the sand substrate and scroll bar topographies can be discerned beneath their peat cover fine sediment plays no role in the confinement of these channels which are maintained by peat levees similar to those encountered in the low sinuosity river channels the recognition of these bedload low sinuosity and meandering river channels now completes the matrix whereby any geometry of river channel can be developed in bedload mixed load and suspended load rivers important aspects of the modern channels for the study of ancient river systems are 1 the confining effect of peat levees which have low preservation potential geologically and 2 in helping to explain river systems which show contradictory evidence of semi arid and more humid climatic conditions the latter may be explained as perennial rivers entering an otherwise semi arid climatic regime from a distant source which provide a shifting more humid overprint to the inherent environmental characteristics

flow transmission along an arid zone anastomosing river cooper creek australia cooper creek is characterized by an exceptionally wide floodplain and a complex system of anastomosing channels which together can accommodate a large range of highly variable flows in consequence flood frequency curves are unusually steep with minimal tributary contribution over the two study lengths currareva nappa merrie 400 km and nappa merrie innamincka 32 km downstream output is largely controlled by upstream input so that similar flow regimes and hydrograph forms can be maintained despite transmission losses and the variable activation of channels input output relationships defined in terms of total flow volume and peak discharge suggest that above a threshold flow of about 25 duration transmission losses exceed 75 on average over the currareva nappa merrie length the large difference in absorption between primary channels on the one hand and subsidiary channels and the floodplain surface on the other means that transmission losses vary non linearly with stage they are relatively low when flow is confined to the primary channels but increase at higher stages as lesser channels and the floodplain are activated early levels do not recur until flows of 0 5 duration are attained when output input ratios increase rapidly with discharge the influences of seasonality and background flow on output discharge are small relative to that of input discharge despite the long river distance peak flows at currareva and nappa merrie are well correlated however over the shorter nappa merrie innamincka length with its more confined system of channels correlations are better and transmission losses less they vary from 60 just above the threshold discharge to lo at flows below 20 duration over this length outflow hydrographs can be effectively estimated by the three parameter muskingum procedure at least on an event by event basis but further application must await additional records to understand fully how the parameters vary in an environment where streamflow is transmitted through a highly variable system of channels

comment on source of the great tsunami of 1 april 1946 a landslide in the upper aleutian forearc by g j fryer et al mar geol 203 2004 201 218

geomorphology and evolution of the late pleistocene to holocene fluvial system in the south eastern llanos de moxos bolivian amazon in the bolivian amazon several paleochannel generations are preserved their wide spectrum of morphologies clearly provides crucial information on the type and magnitude of geomorphic and hydrological changes within the drainage network of the andean foreland therefore in this study we mapped geomorphological characteristics of paleochannels and applied radiocarbon and optically stimulated luminescence dating seven paleochannel generations are identified significant changes in sinuosity channel widths and river pattern are observed for the successive paleochannel generations our results clearly reflect at least three different geomorphic and hydrological periods in the evolution of the fluvial system since the late pleistocene changes in discharge and sediment load may be controlled by combinations of two interrelated mechanisms i spatial changes and re organizations of the drainage network in the upper catchment and or ii climate changes with their associated local to catchment scale modifications in vegetation cover and changes in discharge inundation frequencies and magnitudes which have likely affected the evolution of the fluvial system in the llanos de moxos in summary our study has revealed the enormous potential which geomorphic mapping and analysis combined with luminescence based chronologies hold for the reconstruction of the late pleistocene to recent fluvial system in a large portion of amazonia

t waves from the 1998 papua new guinea earthquake and its aftershocks timing the tsunamigenic slump t waves recorded at hydrophone and seismic stations following the papua new guinea earthquake of 17 july 1998 and its aftershocks show that a small event at 09 02 gmt featured source properties incompatible with an elastic dislocation of appropriate body wave magnitude m b 4 4 these include an exceptional duration 47 s at the wake island hydrophone station wk31 a spectrum rich in high frequencies 7 to 12 hz and a generally low spectral amplitude these characteristics can be explained by the model of an underwater slump accelerating from a standstill and eventually slowing down the relocation of the 09 02 event is compatible with its location within an amphitheater inside which shipboard cruises in 1998 and 1999 documented the presence of a 4 c km3 geologically fresh slump we propose that the slump took place at 09 02 on 17 july 1998 i e 13 minutes after the mainshock and that it generated the locally catastrophic tsunami whose properties amplitude and distribution of runup timing could not be explained by a dislocation model

forms and processes of two highly contrasting rivers in arid central australia and the implications for channel pattern discrimination and prediction tooth s nanson g c 2004 forms and processes of two highly contrasting rivers in arid central australia and the implications for channel pattern discrimination and prediction geological society of america bulletin 116 7 8 802 816 rae2008

chloride as a signature indicator of soil textural and hydrologic stratigraphies in variable charge deep profiles soil properties that influence water movement through profiles are important for determining flow paths reactions between soil and solute and the ultimate destination of solutes this is particularly important in high rainfall environments for highly weathered deep profiles we hypothesize that abrupt changes in the distribution of the quotient qt silt sand clay reflect the boundaries between textural units or textural ts and hydrologic hs stratigraphies as a result qt can be used as a parameter to characterize ts and as a surrogate for hs secondly we propose that if chloride distributions were correlated with qt under non limiting anion exchange then chloride distributions can be used as a signature indicator of ts and hs soil cores to a depth of 12 5 in were taken from 16 locations in the wet tropical johnstone river catchment of northeast queensland australia the cores belong to nine variable charge soil types and were under sugarcane saccharun officinarum s production which included the use of potassium chloride for several decades the cores were segmented at i m depth increments and subsamples were analysed for chloride ph soil water content theta clay silt and sand contents selected bores were capped to serve as piezometers to monitor groundwater dynamics depth incremented qt theta and chloride correlated each individually significantly with the corresponding profile depth increments indicating the presence of textural hydrologic and chloride gradients in profiles however rapid increases in qt down the profile indicated abrupt changes in ts suggesting that qt can be used as a parameter to characterize ts and as a surrogate for hs abrupt changes in chloride distributions were similar to qt suggesting that chloride distributions can be used as a signature indicator of qt ts and hs groundwater data indicated that chloride distributions depended at least partially on groundwater dynamics providing further support to our hypothesis that chloride distribution can be used as a signature indicator of hs copyright c 2005 john wiley sons ltd

side valley tributary fans in high energy river floodplain environments sediment sources and depositional processes navarro river basin california side valley tributary fans within the main axial valley river floodplain system are integral components of the sediment assemblage characterizing floodplains in the high energy navarro river basin california laboratory analyses of subsurface core and auger samples from four study sites reveal that sediment size distributions within the floodplain are controlled by spatial and temporal variation in sediment sources and depositional processes over 75 of sediment within individual lower fan strata are poorly sorted and include gravel clasts inferred to be contributions from the side valley tributary whereas remaining strata are composed of fine sediment less than 2 mm without gravel high water marks indicate that portions of the side valley tributary fans are episodically inundated by axial valley overbank flow a factor that influences fan relief and profile thus two dominant sources supply sediment to this transitional environment side valley tributaries and the axial valley river the transport and depositional processes that supply sediment to the fans operate under three conditions 1 tributary debris or fluvial flows and selective entrainment of fines by fan surface flows deposit sediment when there is no overbank flow from the axial channel 2 overbank flow deposits sediment derived from the axial valley river when there is no tributary input and 3 tributary flows deposit sediment while the floodplain is inundated by floods from the axial valley river the mixing and interlayering of sediment from these disparate sources within the active floodplain illustrate the significance of both hillslope floodplain and channel flood plain interactions in high energy fluvial systems with floodplains

shoreline processes and the age of the lake lahontan highstand in the jessup embayment nevada the well developed shoreline record of pluvial lake lahontan in the jessup embayment nevada is used to refine the history of late pleistocene lake level fluctuations and to assess controls on shoreline development and distribution controls on the strength and type of shorelines developed include local slope the amount and characteristics of sediment available for transport the availability of accommodation space and length of time the lake level resides at a particular shoreline elevation at the sehoo highstand and during the early part of the regression strong storm winds and waves from the south southeast set up a clockwise net shore drift pattern near the head of the embayment although significant differences in local slope geometry of the shoreline and wave energy existed in the embayment crestal heights of constructional shoreline features formed at the highstand vary 2 6 m in elevation and hence provide a relatively precise marker of the highstand elevation radiocarbon dating of a camel bone preserved in high shoreline deposits indicates that the lake reached its highest elevation of 1338 5 m in the embayment and receded from that elevation immediately prior to 13 070 60 yr b p similar and slightly older radiocarbon ages on gastropod shells preserved in barrier deposits at 1327 m 13 280 110 yr b p and 1331 m 13 110 110 yr b p suggest that the final rise to the highstand was very rapid and that the lake maintained its highest stand for a very brief period of time perhaps only for years or decades the brevity of the highstand is reasonable in light of the recent formation of similar barrier features in modern pyramid lake which formed in less than seven months due to a rapid increase in lake level

climate sea level and tectonic controls on sediment discharge from the sepik river papua new guinea during the mid to late pleistocene abstract amongst the rivers draining the mountainous islands of the indonesian archipelago the sepik river of papua new guinea is the largest contributor of solute and particulate material to the world ocean sites u1484 and u1485 drilled during international ocean discovery program iodp expedition 363 provide a continuous 555 kyr long high resolution record of mainly siliciclastic slope sedimentation on the northern continental margin of png just offshore the mouth of the sepik river sedimentological analysis based on a combination of smear slide petrography particle size analysis high resolution physical properties track data and visual core description offers an unprecedented opportunity to investigate the evolution of this major tropical river throughout changing climate and sea level conditions during the mid to late pleistocene the sites u1484 and u1485 sediment records exhibit a dramatic lithologic change at 370 ka the oldest deposits are dominated by pelagic mud suggesting that the coarser grained terrigenous discharge from rivers draining the new guinea highlands including a proto sepik river was captured before reaching the ocean when the sepik river basin was an epicontinental sea the occurrence of coarser grained mass gravity mainly hybrid flows after 370 ka suggests that the epicontinental sea became a more restricted shallow water to nonmarine basin probably due to both basin infilling and the uplift of local coastal ranges during the last three glacial interglacial cycles 300 kyr this shallow inland basin was strongly affected by global variations in sea level during sea level lowstands the sepik river cut into older sediments and discharged further offshore onto the shallow continental margins promoting mass gravity flows pelagic mud deposition on the continental margin during the most extreme highstands following deglaciations suggests a return to shallow marine conditions in the sepik basin and repositioning of the river mouth further inland away from the shelf and from the location of the iodp sites this also indicates that variations in terrigenous fluxes during these extreme highstands were not solely controlled by the intensity of the hydrological cycle and that global sea level variations also influenced sediment deposition the sequence is interrupted by several massive grain flow deposits occurring diachronously at sites u1484 and u1485 and related to a period of intensified tectonic activity between 280 ka and 140 ka the sedimentologic characteristics of these mass gravity deposits and their lack of correlation between sites are interpreted as resulting from channelized flows along margin parallel fault controlled channels caused by local and regional failures of the continental margins including the area of the yalingi canyon 50 km north of the sites where large tsunamigenic events have also occurred in recent years time series analyses of magnetic susceptibility and natural gamma radiation proxies for sand and clay content respectively indicate that river discharge fluxes were modulated at orbital frequencies including obliquity scale cycles which suggests that precipitation and river discharge were not only linked to precessionally driven shifts in the mean position of the intertropical convergence zone but also to high latitude climate change

the okavango fan and the classification of subaerial fan systems abstract controversy exists over the classification of fluvially formed subaerial fans authors either restrict alluvial fans to debris flow dominated types or extend the spectrum to fans dominated by braided rivers the okavango fan provides an end member which extends this spectrum to fans dominated by meandering and low sinuosity rivers the fan is a large 150 km radial axis shallowly sloping 0 00036 highly vegetated subaerial fan which can be subdivided into four subenvironments these are 1 the entry corridor or panhandle characterized by single and anastomosing meander belts 2 the upper fan characterized by meander belts diverging from the fan apex comprising peat confined meandering channels with interchannel swamps forming thick peats 3 the middle fan with highly confined single and anastomosing low sinuosity rivers and less common prograding meander belts whose channels are confined by thick peats with however little chance of peat preservation and 4 the lower fan in which annual floods from relatively unconfined channels spread over the fan surface and interact with pre existing aeolian and lacustrine deposits with the recognition of this new fan type the spectrum of subaerial fan types can be expressed in terms of 1 debris flow dominated fans of which the death valley fans are a member 2 braided river dominated fans of which the kosi fan is a member and 3 low sinuosity meandering losimean river dominated fans of which the okavango fan is a member this spectrum can be expressed in terms of variation in slope maximum size and percentage of surface vegetation but crucial to the evolution of the various fan types is variation in the flashy to continuous nature of the discharge and the degree of channel confinement evident on the fan surface comparable ancient examples of the three fan types are recognizable many of which provide intermediates between the ideal end members debris flow dominated and braid dominated fan types are known from throughout earth history however the losimean fan type because of its reliance on confining vegetation may only have developed after the devonian period the spectrum of subaerial fan types can be expressed on a triangular field of variation with the vertices defined by the relative importance of the processes which shaped a particular fan system be they debris flows processes associated with braided rivers or processes associated with meandering and low sinuosity rivers

fluvial aeolian interactions part i modern systems two modern fluvial aeolian depositional systems great sand dunes national monument colorado and the mojave river wash california are remarkably similar in spite of different climates sizes fluvial sediment textures and relative directions of aeolian and fluvial transport dune growth and migration and deflation of blowouts create 8 10 m of local relief in unflooded aeolian landscapes there are six prominent fluvial aeolian interactions 1 fluvial flow extends into the aeolian system until it is dammed by aeolian landforms 2 interdune areas overbank interdunes upstream of aeolian dams and alongside channels are flooded 3 water erodes dunes alongside channels and interdunes 4 flood waters deposit sediment in interdune areas 5 fluvially derived groundwater floods interdunes interdune playas 6 wind erodes fluvial sediment and redeposits it in the aeolian system unique and characteristic sediments are deposited in overbank interdunes and in interdune playas reflecting alternate fluvial and aeolian processes and rapidly changing flow and salinity conditions these fluvial aeolian interdune deposits are characterized by irregular concave up bases and flat upper surfaces containing mudcracks or evaporite cement characteristic low relief surfaces form in aeolian systems as an effect of flooding fluvial deposits are resistant to aeolian deflation aeolian sand is preserved when flood sediments are deposited around the bases of the dunes thus repetitive fluvial and aeolian aggradation tends to be stepwise as interdune floors are suddenly raised during floods the effects of flooding should be easy to recognize in ancient aeolianites even beyond the area covered with overbank muds

crevasse splays from the rapidly aggrading sand bed braided niobrara river nebraska effect of base level rise base level rise of 2 35 m on the niobrara river has resulted in aggradation of the channel belt and a recent avulsion overbank areas have become flooded by rising groundwaters and more than eight crevasse splays have formed between 1993 and 1997 two crevasse splays situated on the west and east sides of the niobrara have been studied using ground penetrating radar gpr shallow boreholes and topographic surveys the vibracores and gpr profiles provide a nearly three dimensional view of the architecture of crevasse splay deposits the east splay was initiated in the winter of 1993 94 and has expanded to cover an area 200 m by 1000 m with sediment up to 2 5 m thick the west splay which was initiated by the opening of a crevasse channel through a levee in the autumn of 1995 covers an area 150 m by 250 m with up to 1 2 m of sand deposited in a single year the niobrara splays are sand dominated and characterized by bedload deposition within channels 5 30 m wide and 0 5 2 m deep with the development of slipfaces where splays prograde into standing bodies of water sedimentary structures in cores include horizontal lamination ripple lamination and sets of cross stratification there is a slight tendency for splays to coarsen up but individual beds within the splays often fine up the abundance of crevasse splays on the niobrara river contrasts with other braided river floodplains in the niobrara crevasse splay formation followed aggradation within the channel belt which occurred in response to base level rise the link between crevasse splays channel aggradation and base level rise has important implications for the interpretation of ancient braided river and floodplain sequences it is suggested that crevasse splay deposits should be an important component of aggrading fluvial sediments and hence should be preserved within the rock record in this case the aggradation and crevassing have been tied to a rise in base level elevation and it is suggested that similar deposits should be preserved where braided rivers are affected by base level rise for instance during transgression and filling of palaeovalleys

active deformation in the new guinea fold and thrust belt seismological evidence for strike slip faulting and basement involved thrusting the new guinea fold and thrust belt forms a 1000 km long mountain chain running the length of new guinea but its trend is oblique to the predicted convergence direction a large component of left lateral shear across the mountain belt is expected but geological evidence for such motion is ambiguous surface structures in the fold and thrust belt show mountain building by folding and thrusting supposedly thin skinned of pre pliocene continental shelf sediments although some evidence indicates that active faulting penetrates the basement we examine the active deformation of this mountain belt by using teleseismic long period p and sh waveforms short period p waveforms and p wave first motions to determine reliable focal mechanisms and source depths for the 18 largest earthquakes in the new guinea fold and thrust belt since 1964 eight thrust events with seismic moments m0 between 1017 and 2 1018 n m are distributed throughout the thrust belt at depths ranging from 0 5 to 45 km and have steeply dipping fault planes that strike parallel to surface structural trends six of the eight events are between 11 and 25 km deep the steep dips of nodal planes the depths of these earthquakes and the known thicknesses of the sedimentary section show that thrust faulting is not exclusively thin skinned i e confined above a shallow detachment surface but penetrates the crystalline basement at high angles most earthquakes in the western half of the thrust belt including the three largest earthquakes examined m0 5 1018 n m show strike slip faulting with the probable fault plane oriented east west so that displacement is left lateral the nine strike slip earthquakes account for almost 90 of the observed seismic moment in the period 1964 1985 and indicate a seismic slip rate of 5 25 mm a all but one of these strike slip earthquakes are shallower than the thrust earthquakes suggesting that east northeast convergence across the fold and thrust belt is accommodated by a decoupled system of strike slip and dip slip faults while the great height of the mountain belt is an obvious indication that crustal thickening is an important consequence of plate motion in new guinea seismological evidence suggests that translation by strike slip faulting may play a much greater role than previously recognized by analogy in older collisional orogens whose motions can be inferred only from remnant structures and not from seismicity strike slip faulting may have been equally important in accommodating convergence we estimate from seismic moments of earthquakes and from the volume of the mountains that deformation of the new guinea highlands may account for 5 20 of the total convergence between the pacific plate and australia in new guinea

fire storms and erosional events in the idaho batholith in late december 1996 the south fork payette river basin in west central idaho experienced a prolonged storm that culminated on january 1 1997 with intense rain on melting snow that triggered slide failures producing debris flows and sediment charged floods failures occurred in saturated cohesionless grussy colluvium derived from weathered idaho batholith granitic rocks many failures along the south fork payette river originated in ponderosa pine forests burned in the 1989 stand replacing lowman fire an example is the 0 49 km 2 jughead creek basin where a single large colluvial failure produced almost 40 of the total volume eroded from the basin and generated a massive and rapid debris flow failures also occurred in steep unburned and unforested drainages such as hopkins creek in this south facing 0 58 km 2 basin 15 colluvial hollows failed but no single failure produced more than 10 of the total eroded volume sediment transport in hopkins creek occurred by prolonged sediment charged sheetflooding despite vegetation differences sediment yields from the geomorphically similar hopkins creek 42 000 mg km 2 and jughead creek 44 000 mg km 2 basins were quite similar these 1997 erosion events are equivalent to several thousand years of sediment yield at low rates 2 7 30 mg km 2 year 1 measured by short term sediment trapping and gauging in idaho batholith watersheds if similar large events were solely responsible for sediment export recurrence intervals ris of several hundred years would account for higher sediment yields averaged over 10 4 year from idaho batholith watersheds dating of small fire induced sheetflooding events in an early holocene tributary junction fan of jughead creek indicates that frequent small sedimentation events ri 33 80 year occurred between 7400 and 6600 cal year bp with an average yield not greatly exceeding 16 mg km 2 year 1 compared with the holocene average erosion rates during that 800 year period were unusually low suggesting that sediment yields have not been constant over time and that climatic variations and related fire regime changes may exert a strong influence on the probability of major erosional events copyright 2001 john wiley sons ltd

middle holocene avulsion belt deposits in the central rhine meuse delta the netherlands abstract the schoonrewoerd fluvial system in the central rhine meuse delta was active as a rhine distributary between 3900 and 3800 14c years bp based on planform patterns cross sectional facies architecture reconstructed paleodischarge and its short period of activity the schoonrewoerd fluvial system is interpreted to represent a failed avulsion the schoonrewoerd system consists of a complex of ribbon channel sand bodies encased in a lens of clayey deposits and it can be traced for more than 35 km in a downstream direction prominent features of the system are longitudinal facies architecture change with channel sand body width thickness ratio decreasing downstream from 40 to 5 and high lateral facies variability multiple anastomosing sand bodies occur in its upper and middle reaches paleodischarge reconstruction indicates that the schoonrewoerd system was only a minor distributary within the rhine meuse deltaic system specific stream power in the lower reach is estimated to have been low 0 5 to 1 8 w m2 the short period of activity of the schoonrewoerd system suggests that very high floodplain sedimentation rates were associated with the avulsion process with the formation of meters thick fine grained sedimentary successions in 100 years the facies architecture of the short lived schoonrewoerd system is interpreted to reflect the first stages of avulsion broadly analogous to the modern saskatchewan river avulsion in canada smith et al 1989 sedimentology v 36 p 1 23 having escaped from later erosion by a more mature channel belt many other systems often partly eroded with similar facies architecture exist in the west central rhine meuse delta suggesting that avulsion belt deposits are a major component of the holocene delta deposits the facies architecture model of the schoonrewoerd avulsion belt deposits presented in this paper may provide clues for the interpretation of fine grained sedimentary successions in ancient fluviodeltaic deposits

channel fill and sheet flood facies sequences in the ephemeral terminal river gash kassala sudan abstract detailed facies analysis of the river gash fluvial sediments on two dimensional profiles across and along the main channel has revealed a number of facies and two distinct types of sequences channel fill and sheet flood sequences it seems that each sequence type is produced by specific depositional event and both sequences represent two end members for suite of mixed sequences the facies and sequences show rapid lateral variability and they merge and interfinger with each other they also show partial to complete modification due to subsequent floods and stage variation it seems that the thick sediments of the river gash in the kassala area were produced in two phases first by braided channel aggradation and lateral migration second by both channelized and unchannelized sheet flood deposition deposits of these two phases contribute to the sediments of the present day gash fluvial basin in the kassala area the gash sediments show some similarities and differences to those of ephemeral and low sinuosity braided streams the predominance of sheet flood deposits is consistent with the ephemeral flashy high flow regime in the river gash the non conformity of the river gash depositional style with the braided model of fluvial deposition may be due to this semi arid terminal flashy character which has control on the depositional processes and patterns

the orphan tsunami of 1524 on the konkan coast western india and its implications in comparison to the east coast the tsunami hazard for the west coast of india remains under recognized despite the impact in 1945 following a mw 8 1 earthquake in the makran subduction zone in the northern arabian sea the previous occurrences of tsunamis in the arabian sea that would have a bearing on the west coast of india are being debated including the question whether the makran region has the potential to generate greater magnitude earthquakes with this in the backdrop we present here the historical and geological evidence of a tsunami impact zone from a site on the konkan coast of western india located in the village of kelshi the impact zone is preserved within a coastal dune complex that also reveals occupation layers this laterally extending 30 40 cm thick zone coinciding with a habitation level displays varied sedimentary structures including scour fill features and is inter layered with shells at a height of 3 m from the high tide level we attribute these sedimentary features to a tsunami flooding event that was contemporaneous with the transportation of shells dated at 1508 1681 ce the geological inference matches with the description by the portuguese fleets of a sea disturbance in 1524 ce reported from dabhol not far from kelshi and also from the gulf of cambay located about 500 km to the north precluding submarine landslide scenarios the modeling results suggest that the high impact in kelshi could have been generated by a mw 9 earthquake sourced in the makran subduction zone it is however intriguing how a mw 9 earthquake in the makran region finds no mention in the historical documentation we underscore the need for fresh efforts along the makran coast to reconstruct the tsunami recurrence history that would generate required validating constraints on the 1524 event if it was indeed generated by a massive earthquake among other mechanisms

tsunamigenic earthquakes past and present milestones we review a number of events which taken individually have significantly affected our understanding of the generation of tsunamis by earthquake sources and our efforts at mitigating their hazards notably through the development of warning algorithms starting with the 1700 cascadia earthquake we examine how significant tsunamis have changed our views in fields as diverse as seismotectonics the diversity of earthquake cycles the development of warning algorithms the response of communities at risk to warnings and their education the latter being either formal or rooted in ancestral heritage we discuss in detail lessons from the 2004 sumatra disasters and review the performance of warning centers and the response of affected populations during the nine significant tsunamis which have taken place since 2004

fluvial processes and cyclicity in terminal fan deposits an example from the late devonian of southwest ireland abstract the gun point formation is a sandstone dominated sequence approximately 1 5 2 5 km thick which forms part of a major 6 km late devonian alluvial basin fill succession in southwest ireland it is interpreted as the deposits of a southerly flowing terminal fan system which operated under a semi arid climate the proximal zone was characterized by low sinuosity gravelly feeder channels which passed downstream into a medial zone dominated by a sandy braidplain further south in the distal zone phases of high energy flood activity were centred on transient low sinuosity ephemeral channels and were separated by more quiescent periods of shallow sheetflooding subaerial exposure and non deposition sedimentary parameters such as set thickness coset thickness channel sand body density and maximum sand body thickness all exhibit regular cyclic fluctuations with a periodicity of 160 180 m the cycles are interpreted as evidence of regular discharge variations which may have been a response to the 412 ka orbital eccentricity cycle a second periodicity of approximately 700 m has also been detected and is thought to reflect long term variations in basin subsidence

kosi megafan historical records geomorphology and the recent avulsion of the kosi river abstract it has been proposed that the kosi river continuously migrated 113 km westward across the surface of the megafan over the last two centuries examination of a number of old maps published between 1760 and 1960 shows that during most of this period the kosi river occupied a position slightly east of the megafan axis the apparent channel movement shown in these maps is oscillating in nature and not unidirectional instead of encountering deposits left behind by a sweeping braided kosi like stream a preliminary study of the uppermost 2 5 m succession in the north central part of the megafan reveals overwhelming dominance of meandering stream deposits assuming the existing notion of kosi river migration the rate of deposition averaged over 100 200 years for the uppermost 5 10 m of megafan deposits works out to be unusually high 50 mm y all these observations question the soundness of the hypothesis of rapid westward migration of the kosi river over the last two centuries the existing facies model for the uppermost 8 10 m of the megafan deposits also appears untenable the three dimensional geometry of the kosi megafan is similar to those of typical alluvial fans but with much gentler gradient 0 05 0 01 and with larger area 10 000 km 2 based mainly on the patterns of paleo and modern channels recognised in the satellite images three major accretionary lobes can be identified on the kosi megafan relative age of the lobes determined from the truncating relationship of the paleochannels indicates a random shift of the trunk channel forming these lobes similar multilobate form and evidences of random switching of the loci of lobe aggradation are also found to be common in the tista and taquari megafans the factors known to favour avulsion and the results of the recent simulation studies of alluvial deposits are inconsistent with the notion of unidirectional shift of the channels for more than 100 km across the entire megafan surface this study suggests that the relocation of the kosi river in the past was through random nodal avulsion rather than systematic unidirectional shift the recent avulsion of the kosi channel by a large distance to the east follows this expected pattern further study and age dating is required for a comprehensive understanding of the depositional dynamics of the megafan and the pattern of channel movement on it future flood predictions and disaster management plans should be based on such comprehensive understanding

teleseismic estimates of radiated seismic energy the e m 0 discriminant for tsunami earthquakes we adapt the formalism of boatwright and choy for the computation of radiated seismic energy from broadband records at teleseismic distances to the real time situation when neither the depth nor the focal geometry of the source is known accurately the analysis of a large data set of more than 500 records from 52 large recent earthquakes shows that this procedure yields values of the estimated energy ee in good agreement with values computed from available source parameters for example as published by the national earthquake information center neic the average logarithmic residual being only 0 26 units we analyze the energy to moment ratio by defining log10 ee m0 for regular earthquakes this parameter agrees well with values expected from theoretical models and from the worldwide neic catalogue there is a one to one correspondence between values of that are deficient by one full unit or more and the so called tsunami earthquakes previously identified in the literature as having exceedingly slow sources and believed due to the presence of sedimentary structures in the fault zone our formalism can be applied to single station measurements and its coupling to automated real time measurements of the seismic moment using the mantle magnitude mm should significantly improve real time tsunami warning

sequence model for coastal plain depositional systems of the upper triassic betic cordillera southern spain abstract the deposits of the upper triassic of the subbetic zone betic cordillera offer an example of semi arid fluvial deposits passing into shallow water facies through a mud flat environment from the study of the vertical changes in facies a sequence model is proposed for the upper triassic succession relating for each systems tract the changes in sea level the accommodation space and the evolution of the facies within a coastal plain depositional system the lowstand depositional system is made up of a package of thick amalgamated sandstone strata limited below by an erosive surface with little incision these are sheet flood deposits and channel fills which form part of an extensive alluvial system in which wide but shallow water courses appear with the development of extensive sand bars these sandbodies from the lowstand phase often contain mudrock intraclasts plant remains and erosive surfaces the accommodation space being extremely limited the preservation of the floodplain or mud flat deposits and palaeosols is practically nil the result is an amalgamation of extensive sandbodies with fine intercalated claystone levels the transgressive depositional systems consist mainly of a red claystone series although the first sediments of these systems are composed of sandstone with major claystone intercalations these lower sandy levels of the transgressive phase do not exceed 50 cm in thickness and usually contain burrows and small scale sedimentary structures in the intermediate part of the red claystone series of this transgressive episode of saline mud flat facies there are sandstone levels of a little developed fluvial system with channels which migrate laterally due to the rise of the base level in addition the predominance and the great development of the red claystone facies reflect the increase in the accommodation space which permitted a greater accumulation of sediments during a transgressive phase than during the lowstand phase in the upper part of the transgressive depositional systems beds of calcrete and carniolar limestone are common indicating a decreased sedimentation rate the generation of accommodation space begins to slow down leading to the enlargement of sandbodies corresponding to terminal fan deposits friend 1978 these developed over a flat topography where the flow scattered and expanded laterally in the highstand phase the accommodation space reduced even more and the sedimentation rate is lower favouring a great development of pedogenic carbonates furthermore sand deposition was reduced or nil and the gradient of the slope was low so that marine floods over the coastal plain were more frequent permitting the precipitation of carbonates and sulphates in coastal salt pans

terminal fans and the ganga plain tectonism a study of neotectonism and segmentation episodes of the indo gangetic foreland basin india abstract the study of spatial and temporal distribution of holocene terminal inland fans in the indo gangetic foreland basin suggests that the segmentation of the basin was initiated at 9 3 ka and continued up to 0 75 ka in three distinct episodes the earliest episode 9 3 7 3 ka was exclusively confined in the upper gangetic plain this episode covers 29 of total time span and contributes 13 of total faults including their reactivations development of six faults associated with terminal fans having large age gaps indicate relatively slow rate of faulting activities in the early holocene the second faulting episode was started at 6 4 ka and continued up to 2 3 ka covering 60 time of the total time span and contributed 69 of total faults including their reactivations though in most of the time the faulting events were confined in the upper gangetic plain but development of few faults in the middle gangetic plain in the middle of this episode shows a transitional shift of tectonic front from the upper to the middle gangetic plain the third faulting episode 1 5 0 75 ka is mainly confined in the middle gangetic plain this episode covers 11 time of the total time span and contributes 18 of faults out of the eight faults seven of them are in the middle gangetic plains though these three episodes have contributed in segmentation of the gangetic plains but the second episode was responsible for major segmentation of the region two major tectonically stable periods 7 3 6 4 ka and 2 3 1 5 ka and three minor periods in duration of 0 5 ka have been observed in the region episodic development of faults in individual tectonic blocks indicates that the stress distribution along the plains is non uniform which can also be correlated to the adjacent corresponding segments of the himalayan tectonics it has been observed that in each fault bounded block the faulting events start slowly and later becomes more frequent previous work pointed out four tectonically active episodes between the ghaghara and kosi rivers with the oldest faulting event at 7 89 ka however the region west of it i e between the ghaghara and ghaggar rivers which includes rest of the upper gangetic plain shows that neotectonic activities are earlier than 7 89 ka the oldest faulting event observed by previous study the youngest faulting episode of the present study coincides with that of previous study and suggests that the region between the gandak and kosi rivers is tectonically most active at present the tectonically stable periods pointed out in the previous study between the ghaghara kosi region is occupied by the faulting events in the upper gangetic plains hence instead of four tectonically active episodes the whole ganga plain witnesses three segmentation episodes with two major intervening stable periods the change of orientation of the faults in the plain may be correlated to directional change of indian plate motion differential convergence and upliftment rates along the himalayan front and the spatial extension of subsurface precambrian basement ridges into the plains

volcano collapse and tsunami generation in the bismarck volcanic arc papua new guinea during a cruise on the r v kilo moana in 2004 we mapped 12 debris avalanches from volcanoes in the bismarck volcanic arc estimated their sizes and computed the size of potential tsunami run up in major local population centers from these features we used the towed side scan instrument hawaii mr1 the hull mounted em120 system for swath bathymetry and backscatter intensity a shallow penetration chirp system several bottom camera tows and selected cores we calibrate our computations with the known tsunami run up of the ritter collapse even the small collapses may have had significant run up on near by coastlines had any of the collapses we have identified occurred in modern times each would affect a presently populated region of the coastline to a moderate or significant degree

processes facies and architecture of fluvial distributary system deposits abstract there is evidence from the stratigraphic record of examples of fluvial deposits that were the products of deposition from river systems which had decreasing discharge down flow and transitions from proximal channelised to distal unconfined flow these deposits form fan shaped bodies several tens of kilometres in radius and their stratigraphic architecture is aggradational with no evidence of deep incision driven by base level fall the fluvial systems that generated these deposits formed under conditions for which there is no complete analogue today an endorheic basin with a relatively arid climate adjacent to an uplifted area with higher precipitation a conceptual model for fluvial systems of this type has therefore been built on the basis of outcrop examples and a consideration of the controls on sedimentation proximal areas are characterised by amalgamated coarse pebbly and sandy channel deposits with little preservation of overbank facies channel dimensions are generally smaller in the medial areas but sizes are variable deposits are of braided meandering and simple channels which show varying degrees of lateral migration the channel fills may be mud or sand with overbank flow processes playing an important role in filling channels abandoned on the floodplain after avulsion the proportion of overbank deposits increases distally with sheets of sand deposited as lateral and terminal splays by unconfined flow interconnection of sandstone bodies is poor in the distal areas because channel fill bodies are sparse small and are not deeply incised the radial pattern of the sediment body forms by the repeated avulsion of channels active channels build up lobes on the alluvial plain and rivers switch position to follow courses on lower lying areas the term fluvial distributary system is here used to describe a river system which has a downstream decrease in discharge and has a distal zone which is characterised either by terminal splays on to a dry alluvial plain or a lake delta during periods of lake highstand

shifting of the kosi river northern india the kosi river shifts laterally over the himalaya foreland plain by continual minor cutoffs and bank cutting and by episodic major shifts across watersheds by moving into and then out of preexisting adjacent less actively aggrading streams migration is unidirectional because after a channel is filled to instability floodwater will drain preferentially into a new adjacent low rather than across it to the next watershed or back to the last abandoned channel major shifts seem stochastic and autocyclic they do not correlate with the many severe quakes and floods that undoubtedly helped prime the system for shifts

seismotectonics of new guinea a model for arc reversal following arc continent collision the structure and evolution of the northern new guinea collision zone is deduced from international seismological center isc seismicity 1964 1985 new and previously published focal mechanisms and a reexamination of pertinent geological data a tectonic model for the new guinea margin is derived which illustrates the sequential stages in the collision and suturing of the bewani toricelli adelbert finisterre huon new britain arc to central new guinea followed by subduction polarity reversal in the west east of 149 e the solomon plate is being subducted both to the north and south bringing the new britain and trobriand forearcs toward collision west of 149 e the forearcs have collided and together they override a fold in the doubly subducted solomon plate lithosphere which has an axis that is parallel to the strike of the ramu markham suture and that plunges westward at an angle of 5 beneath the coast ranges of northern new guinea active volcanism off the north coast of new guinea is related to subduction of the solomon plate beneath the bismarck plate active volcanism of the papuan peninsula and quaternary volcanism of the new guinea highlands are related to slow subduction of the solomon plate beneath the indo australian plate along the trobriand trough and the trough s former extension to the west respectively from 144 148 e seismicity and focal mechanisms reveal that convergence between the sutured bismarck and indo australian plates is accommodated by thrusting within the finisterre and adelbert ranges and compression of the new guinea orogenic belt together with basement involved foreland folding and thrusting to the south the finisterre block overthrusts the new guinea orogenic belt whereas the adelbert block is sutured to new guinea and overthrusts the oceanic lithosphere of the bismarck sea along the new guinea trench west of 144 e seismicity defines a southward dipping wadati benioif zone and focal mechanisms indicate oblique subduction only this oldest westernmost portion of the collision has progressed past suturing to a full reversal in subduction polarity

twenty five years of progress in the science of geological tsunamis following the 1992 nicaragua and flores events we review a set of 47 tsunamis of geological origin triggered by earthquakes landslides or volcanoes which have occurred over the past 25 years and provided significant new insight into theoretical experimental field or societal aspects of tsunami science among the principal developments in our command of various aspects of tsunamis we earmark the development of the w phase inversion for the low frequency moment tensor of the parent earthquake the abandonment of the concept of a maximum earthquake magnitude for a given subduction zone controlled by simple plate properties the development and implementation of computer codes simulating the interaction of tsunamis with initially dry land at beaches thus introducing a quantitative component to realistic tsunami warning procedures and the recent in situ investigation of current velocities in addition to the field of surface displacements during the interaction of tsunamis with harbors continued research remains warranted notably in the field of the real time identification of tsunami earthquakes whose tsunamis are larger than expected from their seismic magnitudes especially conventional ones the recent tragedy during the 2018 krakatau flank collapse along a scenario which had been quantitatively forecast also emphasizes the need for a continued effort in the education of the populations at risk

fluvial evaporitic and shallow marine facies architecture depositional evolution and cyclicity in the sivas basin lower to middle miocene central turkey abstract lower to middle miocene rocks in the karayun region of the sivas basin are represented by the agilkaya and egribucak formations forming a 4 km thick continuous section each formation is subdivided into three members representing similar lithofacies the lower members are made up of fluvial sheet sandstone and red mudstone that migrated laterally on a flood basin within a semi arid fan system the middle members are composed of bedded to massive gypsum and red green mudstone of a coastal and or continental sabkha environment they are intercalated with lagoonal dolomitic limestone and bituminous shale in the agilkaya formation and fluvial red pink sandstone red mudstone in the egribucak formation the upper members are made up of shallow marine fossiliferous mudstone and sandy limestone rapid vertical and horizontal facies changes in both formations reflect the locally subsiding nature of this molassic basin the overall section can be also subdivided into three orders of fining upward cycles type i cycles correspond to the agilkaya and egribucak formations each around 2 km thick and indicate two long term transgressive phases controlled by tectono eustatic factors type ii cycles 140 m thick on average are formed by alternations of fluvial sheet sandstone and red mudstone capped by up to 50 m thick red flood basin mudstone a 400 ka period milankovitch cyclicity related to astronomical climatic fluctuations is suggested as a governing mechanism although subsidence cannot be excluded the existence of laterally persistent fluvial sheet sandstone overlain by red mudstone that forms fining upward type iii cycles 10 m thick on average is attributed to changes in subsidence rate rhythmic alternations between gypsum beds and red green mudstone and or dolomitic limestone and bituminous shale observed in the middle members might be related to minor periodical climatic changes rather than to tectonics

re examination of the source mechanism of the 1998 papua new guinea earthquake and tsunami simulation of tsunami propagation and runup of the 1998 papua new guinea png earthquake tsunami using the detailed bathymetry measured by jamstec and adding bathymetric data at depths less than 60 m is carried out reproducing the tsunami energy focus into warapu and arop along the sissano lagoon however the computed runup heights in the lagoon are still lower than those measured even if the error in estimating the fault parameters is taken into consideration computational results are similar analysis by the wave ray method using several scenarios of the source size of the tsunami and location by the wave ray method suggests that a source characterized by small size in water 1 000 m deep approximately 25 km offshore the lagoon best fits the arrival determined from the interviews with eyewitnesses a two layer numerical model simulating the interaction of the tsunami with a landslide is employed to study the behavior of a landslide generated tsunami with different size sand depths of the initial slide just outside the lagoon a landslide model with a volume of 4 8 109 m3 is selected as the best in order to reproduce the distribution of the measured tsunami runup in the lagoon the simulation of a tsunami generated in two stages fault and landslide could show good agreement with the runup heights and distribution of the arrival time but a time gap of around 10 minutes remains suggesting that a tsunami generated by the mainshock at 6 49 pm local time is too small for people to notice and the following tsunami triggered by landslide or mass movement near the lagoon about ten minutes after the mainshock attacked the coast and caused the huge damage

distribution of palaeosols and deposits in the temporal evolution of a semiarid fluvial distributary system bauru group upper cretaceous se brazil abstract the stratigraphic and sedimentological knowledge of the bauru group upper cretaceous se brazil is still generally insufficient and controversial a sedimentological and palaeopedological study allowed to interpret the south eastern portion of the bauru group according to the model of a fluvial distributary system this work has two objectives 1 to include palaeosols in the interpretation of a fluvial distributary system and 2 to give detailed information on the sedimentological and stratigraphic features of the se portion of the bauru group in order to support biostratigraphical taphonomic and palaeoecological studies in the south eastern portion of the bauru group three genetic stratigraphic units were described and interpreted here informally called lower intermediate and upper units the lower unit is constituted of muddy sandstone salt flat deposits and sandstone sheet deltas deposits and is interpreted as a basinal part of a fluvial distributary system the intermediate unit is formed of very fine to fine grained sandstone filled ribbon channel and sandy sheet shaped beds suggesting a distal or medial portion of a fluvial distributary system the upper unit does not match with the present models of the fluvial distributary system because mostly constituted of moderately developed well drained medium to fine grained sandstone palaeosols which testify pauses of sedimentation to the order of 104 years preserved features of sedimentary structures suggest that the parent material was formed by occasional catastrophic unconfined flows this unit may represent the most distal portion of a fluvial distributary system generated by retrogradation of the alluvial system due to aridification of the climate the upper unit may be interpreted also as proximal portion of fluvial distributary system if considering the coarser grained and the well drained palaeosols however the absence of channel deposits makes this interpretation unconvincing

splay formation along the lower reaches of ephemeral rivers on the northern plains of arid central australia abstract splays are common features of many rivers and deltas forming as a result of overbank flooding and sediment deposition but they have rarely been described from modern dryland settings this paper investigates splay formation along the lower reaches of ephemeral rivers on the northern plains of arid central australia here splays vary from small lobate or tongue shaped features 1 km long to larger elongate features up to 4 km long and are supplied with rare floodwater and sediment through well defined breaches in the upper parts of the main channel banks in proximal and medial parts splay channels are incised up to 2 m into pre splay fine grained floodplain sediments but remain elevated between 0 5 m and 2 m above the main channels only in the very distal parts are splay channels less deeply incised either grading into the floodplain surface or terminating as sediment lobes that are deposited upon the floodplain aerial photographs and field observations indicate that many splays develop rapidly during large floods and are modified during infrequent subsequent floods four main stages of splay development are proposed 1 aggressive overbank flow results in bank line breaching and channel scour on the floodplain but little sediment deposition 2 coarse bed sediment is diverted from the main channel preventing further deepening at the bank line breach and slowing channel scour 3 increasing coarse sediment transport through the bank line breach and scoured channels leads to the formation of distal sediment lobes 4 subsequent floods divert around these distal lobes sometimes leading to further channel scour and lobe formation on the northern plains splays contribute to downstream decreases in the discharge and size of the main channels and splay deposits form local accumulations of gravelly sand in the predominantly fine grained floodplain successions some splays ultimately may evolve into distributaries or anabranches the dominantly erosional bases of these splay channels contrast with typical descriptions of many humid region splays but they do not display any geomorphological or sedimentological features that are necessarily diagnostic of formation in a dryland setting

a theoretical comparison of tsunamis from dislocations and landslides we use simple physical models to evaluate and compare the orders of magnitude of the energy generated into a tsunami wave by seismic dislocations and underwater slumps we conclude that the two sources can generate tsunamis of comparable total energy however the slumping source is shown to be fundamentally dipolar in nature which results in a low frequency deficiency in the far field these simple conclusions corroborate the interpretation of the 1998 papua new guinea tsunami as being generated by an underwater slump

alluvial fans and fluvial distributary systems oligo miocene northern spain contrasting processes and products sediments of alluvial fans and distributive fluvial sediments were deposited by contrasting processes during the oligo miocene in the north central ebro basin northern spain the coeval depositional systems can be separated on the basis of lithofacies criteria a number of localized deposits each covering only a few square kilometers and lying adjacent to the south pyrenean thrust front are made up of beds of poorly sorted conglomerate sandstone and mudstone that show a radial decrease in bed thickness and grain size these deposits are interpreted as the products of sheet flood events on alluvial fans that formed at the basin margin covering much larger areas of the basin several thousand square kilometers are conglomerate sandstone and mudstone as lensoid and irregular sheet bodies incised into thin bedded sheets of sandstone and mudstone these are interpreted as the deposits of fluvial systems that are considered to be distributary in form because the channel size and grain size of channel fill deposits decrease down paleoflow and because there is a radial pattern of paleocurrents at the distal margins the fluvial facies interdigitate with ephemeral lacustrine and alluvial plain deposits the deposits of the alluvial fans and the fluvial distributary systems are petrographically distinct reflecting separate source areas important components of the alluvial fan deposits are limestone clasts derived from the adjacent thrust front the deposits of the fluvial systems are mainly sand and subordinate gravel derived from rocks of the axial zone of the pyrenean mountain belt the deposits of these systems interdigitate and there are no transitional forms between the two within this stratigraphic package

digital elevation models in the marine domain investigating the offshore tsunami hazard from submarine landslides digital elevation models dems of seabed relief are now commonly available at a number of scales on a global scale three dimensional 3d relief maps of the ocean floor are derived from satellite gravity measurements validated by single beam echo soundings on a smaller more local scale the development of multibeam bathymetric mapping technology provides detailed seabed data from which dems are derived over the past 30 years multibeam bathymetry has replaced single beam echo soundings as the main tool used to map the sea floor multibeam bathymetry has revolutionized our ability to interpret seabed morphology it has the capability to provide complete seabed coverage and gives a 3d visualization of the seabed not previously available dems derived from multibeam are comparable to those on land one aspect of the improved seabed visualization is in mapping marine geohazards here three dems from papua new guinea hawaii and the indian ocean are presented these dems have been used to investigate submarine seabed failure and volcanic flank collapse in the context of their tsunami hazard for these three areas the dems contribute to an improved interpretational capability in marine geohazards in addition the dems underpin newly developed modelling methodologies of landslide generated tsunami

recognition of the sedimentary architecture of dryland anabranching anastomosing rivers abstract the application of rigorous criteria for identifying fluvial style from sedimentary deposits is crucial if environmental reconstructions from stratigraphy are to be reliable from modern observations it appears that anabranching anastomosing rivers can be divided into separate humid and dryland classes each class has dissimilar characteristics to the other necessitating different criteria for their recognition in the rock record the criteria being used by sedimentologists to recognize deposits of anabranching rivers are derived solely from modern examples in humid regions heavily biased to a few specific cases in canada these criteria are dominated by the concept of ribbon sandstone bodies encased in fine grained floodplain sediment with an overall low sand to mud ratio in the succession there has been a general failure to appreciate that dryland anabranching rivers have characteristics significantly different from these and almost certainly leave a sedimentary record quite dissimilar to that previously expected avulsion or obtrusion the gradual formation of an alternative channel are the characteristic dynamic of anabranching rivers forming and maintaining coexisting multiple anabranch channels avulsion or obtrusion require stream banks to have a high resistance to erosion usually achieved by cohesive bank sediments or the reinforcement of banks by vegetative root mats in some drylands riparian vegetation can be sparse and bank resistance may depend in large part on a high clay content here channel fills are mud dominated and floodplains have a uniform fine grained character which is usually structureless because of intense pedoturbation and some bioturbation the evidence from such present day dryland anabranching rivers suggests that their sedimentary record is likely to be one of laterally extensive mud rich beds with weak or enigmatic fluvial indicators elsewhere dryland anabranching systems are sand dominated their banks reinforced with riparian gallery forests sustained by infrequent flow and a shallow water table though the stratigraphy of these has barely been investigated they are clearly different from humid region anabranching systems for their channels and islands are predominantly sandy anabranching rivers with prominent channel sandbodies separated by muddy islands have never been described from contemporary drylands the interpretation of a dryland origin for ancient stratigraphic successions with this form is made therefore without evidence that they can actually exist in the light of this such interpretations should be reevaluated

fluvial fans myths misconceptions and the end of the terminal fan model we propose that the so called terminal fan facies model should be abandoned since it is flawed on several counts and it is leading to misunderstanding and poor communication rivers in drylands may experience excessive down stream discharge reduction such that they terminate subaerially rather than reach the sea or a lake the facies model predicts that the distal reaches of such rivers form a network of bifurcating distributary channels producing a fan shaped sediment body with downstream thinning and fining of sedimentary units ending in sand filled ribbons encased in mud extensive review of modern rivers has failed to turn up convincing examples that fit the model rivers in drylands do not ubiquitously end in fans fan shaped fluvial bodies are common wherever rivers are released from confinement and the discharge conditions promote frequent avulsion channels on such fans generally do not repeatedly bifurcate downstream where they are seen to do so it can usually be shown they are lacustrine deltas inherited from wetter times the term distributary is being used carelessly and is conveying incorrect understanding of sediment geometry and architecture the proposed synonym of fluvial distributary systems is unsatisfactory as it perpetuates the same misunderstandings reliance on planform alone in analogue selection is highly risky the fluvial fan is a composite sediment body resulting from frequent nodal avulsions in a setting without horizontal constraints channels on fans range in planform as much as any other river the resultant sedimentary record differs little from that expected from non fan fluvial systems except having a regionally radiating orientation when viewed over geological time scales contrary to the implications of the facies model there is no distinctive terminal fan sedimentary succession

empirical constraints on magnitude distance relationships for seismically induced submarine tsunamigenic landslides abstract seismically induced submarine landslide tsunamis here called silts attract growing attention due to their unique setting damage potential and short warning time a question of key importance especially for tsunami early warning is how far can an earthquake trigger a tsunamigenic slump here we investigate the relationships between earthquake magnitude and the maximal distance between the seismogenic fault and the tsunamigenic slumps rf and between the earthquake epicenter and the slump re and propose empirical constraints on these magnitude distance m d relations the 49 identified silts are spread in various seismotectonic and bathymetric settings in different seas around the globe we found that the maximal distance of the tsunamigenic submarine landslide from the parent earthquake grows with the magnitude and is bounded by an envelope constrained by mw as low as 4 9 for several kilometers the 1968 liguria coast italy and as far as 250 km for mw 7 7 the 1819 rann of kachchh india higher earthquake magnitudes also produce silts seemingly distances lower than 250 km however it is suspected that the available data is limited and unable to reflect the true nature of silt s generation generalized empirical relations between the earthquake magnitude mw and the maximal distance from the seismogenic fault to its generated silt rf in km are log rf 1 17 0 49 mw r2 0 78 the empirical distance between the earthquake epicenter and the corresponding tsunamigenic slump re in km is log re 0 87 0 45 mw r2 0 83 although many earthquakes within the m d bounding envelope did not produce tsunamis the successful events still enable the delineation of the m d zone vulnerable to tsunami generation which in turn can be applied to tsunami early warning procedures this is particularly important for near coast inland earthquakes as their tsunamigenic potential might be overlooked

estimation of current plate motions in papua new guinea from global positioning system observations plate tectonic motions have been estimated in papua new guinea from a 20 station network of global positioning system sites that has been observed over five campaigns from 1990 to 1996 the present velocities of the sites are consistent with geological models in which the south bismarck woodlark and solomon sea plates form the principal tectonic elements between the pacific and australian plates in this region active spreading is observed on the woodlark basin spreading centre but at a rate that is about half the rate determined from magnetic reversals the other major motions observed are subduction on the new britain trench seafloor spreading across the bismarck sea seismic lineation convergence across the ramu markham fault and left lateral strike slip across the papuan peninsula these motions are consistent with a 8 2 myr 1 clockwise rotation of the south bismarck plate about a pole in the huon gulf and a rotation of the woodlark plate away from the australian plate second order deformation may also be occurring in particular manus island and northern new ireland may be moving northward relative to the pacific plate at 5 8 mm yr 1 significant at the 95 but not at the 99 confidence level which may suggest the existence of a north bismarck plate

active deformation in eastern indonesia and the philippines from gps and seismicity data in this study we combine global positioning system gps velocities with information on the style of regional seismicity to obtain a self consistent model velocity and strain rate field for the entire eastern indonesia and philippines region in the process of interpolating 93 previously published gps velocities the style and direction of the seismic strain rate field inferred from earthquakes with m0 1 1020 n m from the harvard centroid moment tensor catalog are used as constraints on the style and direction of model strain rates within the plate boundary zones the style and direction of the seismic strain rate field are found to be self similar for earthquakes up to m0 1 1020 n m equivalent to mw 7 3 our inversion result shows the following the java trench which lacks any significant historic seismicity delineates the australian plate au sunda block sunda plate boundary west of the island of sumba east of sumba convergence is distributed over the back arc and banda sea and there is no subduction at the timor trough suggesting that the northern boundary of the au plate runs north of this part of the banda arc through the banda sea in new guinea most motion is taken up as strike slip deformation in the northern part of the island delineating the pacific plate pa au boundary however some trench normal convergence is occurring at the new guinea trench evidence that the strain is partitioned in order to accommodate oblique pa au motion pa au motion is consistent with nuvel 1a direction but 8 mm yr 1 slower than the nuvel 1a estimate for pa au motion the sulawesi trench and molucca sea delineate zones of high strain rates consistent with high levels of active seismicity the sulawesi trench may take up some of the au sunda motion philippine sea plate motion is in a direction slightly northward of the nuvel ia estimate and is partitioned in some strike slip strain rates along the philippine fault and relatively larger trench normal convergence along the philippine trench and on the philippine mainland in the southern philippines and along the manila trench in the northern philippine islands the high level of strain rate along the manila trench is not released by any significant historic seismic activity for the entire eastern indonesia philippines region seismicity since 1963 has taken up 40 of the total moment rate inferred from our model

discontinuity bounded alluvial sequences of the southern gangetic plains india aggradation and degradation in response to monsoonal strength abstract discontinuity bounded late quaternary sequences in the southern gangetic plains himalayan foreland basin reflect floodplain aggradation and degradation in response to forcing by the powerful southwest indian monsoon the major himalayan and cratonic rivers in this area occupy narrow incised valleys and do not inundate the adjoining broad interfluves which display soil development small plains fed rivers lakes eolian deposits and badland ravines however these areas formerly experienced active alluviation because thick floodplain muds underlie the interfluve an age model suggests that interfluve areas near the major rivers aggraded periodically between about 27 ka and 90 ka marine oxygen isotope stages 3 5 they subsequently degraded or accumulated sediment only locally probably reflecting decreased monsoonal precipitation around the last glacial maximum marine isotope stage 2 when major river valleys moved to an underfit condition increased precipitation during the 15 to 5 ka period of monsoon recovery probably increased discharge and promoted incision and widespread badland formation discontinuities at deeper levels reflect earlier degradation phases and are marked by reworked gravel lenses thin channel bodies and carbonate cemented surfaces carbonate veins infilled joints that cut strata below but not above one discontinuity suggest some local tectonic influence there is no evidence that sea level fluctuations influenced stratal patterns in this elevated inland region discontinuity bounded sequences linked to climate change may characterize alluvial successions in many continental settings especially along the cratonic margins of foreland basins where subsidence rates are modest

experimental study of avulsion frequency and rate of deposition in existing models of alluvial architecture it is typically assumed that mean avulsion frequency is independent of sedimentation rate however if avulsion is driven by superelevation of a river bed above its surrounding flood plain one might expect avulsion rate to increase with sedimentation rate we have carried out a series of experiments with laboratory scale fluvial fans in which we measured the frequency of apical avulsions as a function of mean sedimentation rate on the fan avulsion frequency increased strongly with increasing sedimentation rate and then stabilized as mass flows began to influence deposition in the regime of increasing avulsion frequency the added volume of sediment needed to trigger an avulsion decreased with increasing sedimentation rate although our experimental results cannot simply be scaled up to natural rivers they suggest the possibility of coupling between avulsion frequency and sedimentation rate that would be strong enough to change qualitatively the results of existing models of alluvial architecture these models should be applied with caution until avulsion mechanics are better understood

spatial and temporal distribution of inland fans terminal fans between the ghaghara and kosi rivers indicate eastward shift of neotectonic activities along the himalayan front a study from parts of the upper and middle gangetic plains india abstract neotectonic deformation in the indo gangetic plains is primarily manifested by surface ruptures caused by both normal faults and thrust splays the topographic breaks along these faults provide suitable sites for the formation of inland fans terminal fans on the down thrown blocks as these depositional features invariably form along the faults contemporaneously or soon after faulting they have widely been used as potential geomorphic markers in mapping faults in the flat gangetic plains based on this association infrared stimulated luminescence irsl dating of the fans has successfully been used for dating the faulting episodes in the gangetic plains thus the spatial and temporal distribution of inland fans terminal fans suggests migration of faulting activities from west to east with time and successive faulting events occur over periods of several hundreds of years to 10 3 years in the present study the correlation of eighteen dated inland fans terminal fans aligned along the faults and using the surficial and buried soil profiles suggests four deformation episodes 7 89 7 30 ka 5 84 3 99 ka 3 18 2 73 ka and 1 41 0 75 ka in the region between the ghaghara and kosi rivers in the gangetic plains these deformation episodes were witnessed by the development and reactivation of the extensional normal faults transverse to the himalayan frontal thrust hft in the ghaghara rapti interfluve and the thrust splays parallel sub parallel to the hft in the gandak kosi interfan regions the rapti gandak region in the middle serves as a transition zone in between the interfluve and the interfan region and shows both types of fault development at different times six inland fans terminal fans in the ghaghara rapti interfluve were formed between 7 89 and 2 73 ka in three deformation faulting episodes two in each phase the broad age difference between those and strongly developed soils suggests the faulting activities to be less frequent in this region the fan building episodes in the gandak kosi interfan region started at 4 92 ka by the initiation of thrusting activities out of eight inland fans terminal fans five of them were formed during 1 41 0 75 ka in association with various thrust splays these depositional features are characterised by a narrow age gap and weak to no surface soils which indicate early burial by high sediment supply from frequent thrusting activities segments of the plains having a high low population of inland fans terminal fans of narrow broad age gaps and with relatively weakly strongly developed soils lie close to or opposite to the segments having the highest lowest rate of convergence and upliftment of the himalayas along the hft

variability of channel belt dimensions and the consequences for alluvial architecture observations from the holocene rhine meuse delta the netherlands and lower mississippi valley u s a abstract over the past decades many studies have focused on the dimensions of channel belt sand bodies referred to as channel belts in fluvial deposits because of their relevance for hydrocarbon exploration and production some field studies have revealed a significant downstream decrease of channel belt width and width thickness ratio along the length of the channel belt to verify whether this is a common feature in fluviodeltaic settings eight holocene channel belts in the rhine meuse delta the netherlands were selected and one in the lower mississippi valley u s a we determined channel belt geometry width or width thickness ratio using geological geomorphological maps and detailed cross sections based on borings it was found that the width of channel belts encased in cohesive deposits decreases by a factor of 4 to 6 5 in a downstream direction along the length of the channel belts the width thickness ratio decreases by a factor of 2 5 to 5 on the other hand the width of a channel belt incised in a noncohesive substrate remains constant along its entire course these observations are related to longitudinal changes in bank erodibility and stream power it is suggested that bank erodibility is the dominating factor determining the geometric properties of channel belts and the variability therein at least in the rhine meuse delta the currently available alluvial architecture models most likely overestimate sand quantities and connectedness in alluvial successions because channel belt dimensions are held constant in all models we therefore propose that the factors bank erodibility and stream power which influence width and width thickness ratio of channel belts should be incorporated in future alluvial architecture models in order to make more realistic estimates of sand quantities in river deltas

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

source discriminants for near field tsunamis summary we present numerical simulations of tsunami run up in the near field for a data set of 72 models of sources involving both seismic dislocations and landslides by varying one by one the parameters describing the source and the receiving beach we are able to separate their individual influence on the amplitude and distribution of run up which we characterize by forming several dimensionless parameters principally the ratio i 2 of its maximum amplitude to its lateral extent along the beach we find that i 2 remains less than 10 4 for seismic dislocation sources but is greater than this threshold for all physically realistic models of underwater landslides thus it can be used as a discriminant for the nature of the source of a near field tsunami for seismic dislocations we also consider the ratio i 1 of maximum run up to seismic slip on the fault plane and validate numerically the previously suggested rule of thumb that this ratio cannot be much greater than 1 in the case of underwater landslides we show that the distribution of near field run up is primarily controlled by the 2 d wall of water displaced on the ocean surface as an initial condition to the simulation and is practically independent of its extension in the third dimension perpendicular to the beach we apply this approach to nine profiles of tsunami run up obtained experimentally during recent field surveys and show that our method successfully identifies the 1998 papua new guinea tsunami as having been generated by an underwater landslide thus confirming the results of shipboard and hydroacoustic investigations it also strongly suggests a similar mechanism for the generation of the near field aleutian tsunami of 1946 april 1