the undatables quantifying uncertainty in a highly expanded late glacial holocene sediment sequence recovered from the deepest baltic sea basin iodp site m0063 laminated organic rich silts and clays with high dissolved gas content characterize sediments at iodp site m0063 in the landsort deep which at 459 m is the deepest basin in the baltic sea cores

holocene fault scarps near tacoma washington usa airborne laser mapping confirms that holocene active faults traverse the puget sound metropolitan area northwestern continental united states the mapping which detects forest floor relief of as little as 15 cm reveals scarps along geophysical lineaments that separate areas of holocene uplift and subsidence along one such line of scarps we found that a fault warped the ground surface between a d 770 and 1160 this reverse fault which projects through tacoma washington bounds the southern and western sides of the seattle uplift the northern flank of the seattle uplift is bounded by a reverse fault beneath seattle that broke in a d 900 930 observations of tectonic scarps along the tacoma fault demonstrate that active faulting with associated surface rupture and ground motions pose a significant hazard in the puget sound region

physicochemical and biological influences on sedimentary fabric formation in a salinity and oxygen restricted semi enclosed sea gotland deep baltic sea two ca 8000 year long sediment cores from the gotland deep the central sub basin of the baltic sea were studied by means of digital images x radiographs and scanning electron microscopy energy dispersive x ray mineralogical analysis to gain understanding of the physicochemical and biological influences on sedimentary fabric formation in modern and ancient seas with a high flux of organic carbon and associated oxygen stress and depauperate ichnofauna four lithofacies were recognized i sharply laminated mud ii biodeformed mud iii burrow mottled mud and iv sedimentation event bed the sharply laminated and burrow mottled facies dominate the cores as alternating long intervals whereas the biodeformed and sedimentation event facies occur as thin interbeds within the sharply laminated intervals the sharply laminated mud comprises alternating diatom rich and lithic laminae with occasional mn carbonate laminae lamination discontinuity horizons within the laminites where the regular lamination is overlain sharply by gently inclined lamination challenge the traditional view of mud accumulation by settling from suspension but indicate localized accumulation by particle trapping microbial mats and potentially by the rapid lateral accretion of mud from bedload transport the biodeformed interbeds record brief few years to few decades oxic dysoxic conditions that punctuated the anoxic background conditions and permitted sediment surface grazing and feeding by a very immature benthic community restricted to the surface mixed tier the likely biodeformers were meiofauna and nectobenthic pioneers passively imported with currents the sedimentation event interbeds are distal mud turbidites deposited from turbidity currents probably triggered by severe storms on the adjacent coastal areas the turbidite preservation was favoured by the anoxic background conditions the long burrow mottled intervals are characterized by intensely bioturbated fabrics with discrete planolites rare arenicolites polykladichnus and very rare lockeia trace fossils as well as bivalve biodeformational structures which represent shallowly penetrating endobenthic feeding and grazing strategies and permanent dwellings these burrowed intervals represent longer periods several years to few centuries of oxic dysoxic conditions that permitted maturation in the benthos by means of larval settling of opportunistic worm like macrofauna and bivalves resulting in the development of a transition tier these observations imply more dynamic and oxic depositional conditions in gotland deep than previously thought comparison to previous zoobenthic studies in the area allowed discussion of the benthic dynamics and the identification of probable biodeforming and trace producing species implications for current biofacies and trace fossil models are discussed

beach ridge development and sediment supply examples from west africa abstract beach ridges form the dominant mode of holocene coastal progradation in west africa they vary from minor accumulations to massively prograded plains over 100 km long variations in the patterns and morphological expression of these sandy deposits record spatial and temporal changes in various environmental parameters among these sediment supply stands out the importance of this factor is illustrated by the morphological patterns and the current sediment dynamics of minor and major beach ridge plains in this region the simplest beach ridges are related to just one or two sources of sand supply from a nearby source in these examples sand has been supplied by the nearshore zone or by eroding cliffs in many areas beach ridge formation ceased as the sediment supply dwindled because of cliff stabilization or establishment of an equilibrium nearshore profile major beach ridge plains in southern sierra leone and in the bight of benin exhibit complex patterns of development related to a bigger sediment supply from nearshore sources and rivers in southern sierra leone the beach ridge plains have been constructed essentially from sands derived from the nearshore zone locally as in the proximal part of sherbro island shallow nearshore shoals encroached upon by the beach ridge front have led to more massive progradation while engendering complex patterns of beach ridge development the sediment supply has been locally supplemented by sands drifting alongshore from the sewa and moa rivers the sediment supply involved in beach ridge development in the bight of benin highlights the role of longshore drift of sands from the volta delta early stages of progradation were characterized by the development of segmented inner beach ridge barriers separated by still infilling coastal re entrants nearshore sources were particularly important in these early stages of beach ridge progradation as coastal re entrants and their estuaries became infilled following the middle holocene eustatic highstand the longshore drift system evolved from a segmented to a unicellular one the resulting conditions of through drift east of the volta delta allowed for longshore transport of sands from this river for the construction of outer beach ridge barriers over a distance of over 250 km while rivers still actively supply sand to the coast current patterns of beach ridge development depend essentially on the coastal sand transport system which determines either the confinement of incoming sand to the vicinity of the very source area itself its regular delivery to the beach ridge front or its through drift to the local downdrift terminus

necessary conditions for a meandering river avulsion there is as yet no rational basis for predicting the conditions leading to avulsion of a meandering river here we present a conceptual model and quantify it under simplifying assumptions as a first step toward the construction of a stability diagram for avulsion initiation it is assumed initially that a rectangular crevasse channel of arbitrary depth is cut into the levee of a meandering river because the water entering the crevasse channel is derived from relatively high in the main flow it contains low concentrations of suspended solids consequently the crevasse flow is under capacity and the entrance is eroded deepening of the entrance increases the crevasse channel discharge and the concentration of suspended solids supplied because more sediment laden waters are tapped from the deeper flow in the main channel the crevasse entrance is predicted to deepen until its sediment carrying capacity is satisfied by the suspended solids entering from the main channel whether an avulsion will occur for a particular combination of initial conditions depends upon whether there exists steady state hydraulic and sediment transport conditions for crevasse channel depths that are equal to or less than the main channel depth this conceptual model is quantified by writing the unsteady gradually varied one dimensional conservation of mass and momentum equations for water and sediment transport through a main and crevasse channel sediment transport is computed as the integral of a cross sectional mean velocity and a rouse concentration profile solutions show that stable crevasse channels exist only for particular combinations of the initial height of the crevasse bed relative to the water depth in the main channel and the ratio of initial crevasse bed slope to main channel slope

chronology and rates of faulting of ventura river terraces california new evidence concerning the chronology of four late pleistocene terraces of the ventura river near oak view california that are vertically offset and tilted by reverse and reverse flexural slip faults provides a means of estimating rates of fault movement and downcutting by the ventura river radiocarbon ages of charcoal contained within terrace deposits date two of the terraces correlation of soils that have developed on terrace deposits and extrapolation of the rate of vertical displacement of the arroyo parida santa ana fault not a flexural slip fault date the others resulting age estimates for the four main late pleistocene terraces are qt5b 30 000 qt6a 38 000 qt6b 54 000 and qt6c 92 000 yr b p vertical slip rates on flexural slip faults range from 0 3 to 1 1 mm yr and apparently are related to the rate form and mechanics of folding of the north limb of the ayers creek canada larga syncline average rates of downcutting of the ventura river for several intervals during the late pleistocene estimated from the chronology and relative elevation of river terraces north of the arroyo panda santa ana fault upstream from the zone of faulting vary from 0 5 to 1 3 mm yr the range in rates probably reflects variations in local uplift as well as adjustments to changing eustatic sea level climatic conditions and or regional deformation of the western transverse ranges the average rate of downcutting of the ventura river north of the zone of flexural slip faulting is 0 8 mm yr compared with 1 2 to 2 2 mm yr in the deformation zone immediately to the south this apparently indicates that during tectonic deformation there is an approximate balance between the rate of uplift due to faulting and folding and the rate of downcutting by the fluvial system

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

coastal evidence for holocene subduction zone earthquakes and tsunamis in central chile abstract the 500 year historical record of seismicity along the central chile coast 30 34 s is characterized by a series of m 8 0 8 5 earthquakes followed by low tsunamis 10 m but the frequency of such large events is unknown we extend the seismic history of central chile through a study of a lowland stratigraphic sequence along the metropolitan coast north of valparaiso 33 s at this site higher relative sea level during the mid holocene created a tidal marsh and the accommodation space necessary for sediment that preserves earthquake and tsunami evidence within this 2600 yr long sequence we traced six laterally continuous sand beds probably deposited by high tsunamis plant remains that underlie the sand beds were radiocarbon dated to 6200 5600 5000 4400 3800 and 3700 cal yr bp sediment properties and diatom assemblages of the sand beds for example anomalous marine planktonic diatoms and upward fining of silt sized diatom valves point to a marine sediment source and high energy deposition grain size analysis shows a strong similarity between inferred tsunami deposits and modern coastal sediment upward fining sequences characteristic of suspension deposition are present in five of the six sand beds despite the lack of significant lithologic changes between the sedimentary units under and overlying tsunami deposits we infer that the increase in freshwater siliceous microfossils in overlying units records coseismic uplift concurrent with the deposition of five of the sand beds during our mid holocene window of evidence preservation the mean recurrence interval of earthquakes and tsunamis is 500 years our findings imply that the frequency of historical earthquakes in central chile is not representative of the greatest earthquakes and tsunamis that the central chilean subduction zone has produced

errors in the anisotropy of magnetic susceptibility and magnetic remanence of unconsolidated sediments produced by sampling methods samples from glacial varves were obtained by cutting cubes and by pushing plastic cubical containers into the sediment the anisotropy of magnetic susceptibility results show that the mean angular difference in the kmax direction can be altered by 32 by pushing in the sample containers in a north to south versus an east to west direction the values of lineation and q are raised or lowered dependent upon the direction of push and the original fabric direction mean remanence directions can deviate by as much as 43 in a single clay layer dependent upon the direction in which the sample containers are inserted into the sediment corresponding changes in mean intensity of the remanence also demonstrate that the remanence has been affected by pushing in sample containers the overall results underline the need to adopt trustworthy procedures for the sampling of soft sediments deposited by settling and traction

late holocene sea level record in a core from the puget lowland washington abstract diatoms and lithological facies of an 8 45 m core collected from shine swamp 47 52 20 n lat 122 41 45 w long about 2 m above the mean tide level in the northern puget lowland reveal a rise in relative sea level during the past 6000 yr a layer of fresh water peat at a depth of 6 6 6 3 m ca 7000 5000 yr b p indicates a low stand of the sea in early and middle holocene time about 5000 yr ago the rise in relative sea level resulted in accumulation of subtidal or lower intertidal clayey gyttja and gyttja which contain mainly marine and brackish water diatoms 80 95 by about 3500 yr b p the basin had shoaled to upper intertidal levels and peat began to accumulate again while the sea continued its relative rise during the period of this continuous peat growth several alterations in fresh water and marine brackish water diatom assemblages took place indicating slight differences in the contemporaneous sea level rise and vertical peat growth

morphology and recent sediments of the lower anastomosing reaches of the attawapiskat river the attawapiskat river is one of the major low gradient rivers which cross the flat wetlands of the hudson bay lowland it has a nival regime leading to strong short duration spring floods during which considerable amount of sediment is carried for the remainder of the year only organic matter is transported in solution and suspension the land is isostatically rebounding after the pleistocene glaciations the river downcuts through the softer holocene estuarine basal clays and the pleistocene tills to the paleozoic carbonate bedrock the river develops an anastomosing pattern in the lower reaches and it acquires an irregular meandering character inland it does not construct a significantly thick delta as the river borne sediments are dispersed along the coasts by tides longshore currents and ice rafting the river is subjected to frequent ice jams in its lower reaches as warmer southern waters flow toward the still frozen mouth and sea during the jams secondary channels become active floodings develop and sedimentation occurs on the levees ice scours and ice rafted materials affect the river banks greatly the principal sedimentary environments within the river consist of 1 erosional shoals covered by boulder and pebble lags over till 2 sorted coarse to medium sized sands in junction bars downstream from islands these sands frequently develop gas bubbles and they contain characteristic fining upward sequences from boulder pavements at the base grading up into rippled sand with abundant organic matter grading up into laminated silt and sand and organic matter 3 secondary channels which develop thin silty and clay drapes on eroded hard substratum and are filled eventually by thick peats and 4 river banks which show well developed regressive sequences from pleistocene tills at the base overlain by estuarine sparsely fossiliferous clays capped by thin conglomeratic units with abundant reworked macoma balthica shells grading upward into upper tidal flat sand irregularly laminated sand and silt of marshes and regular interbedding of sand silt and organic layers of the levees at the top

spawning sockeye salmon fossils in pleistocene lake beds of skokomish valley washington an assemblage of fossil sockeye salmon was discovered in pleistocene lake sediments along the south fork skokomish river olympic peninsula washington the fossils were abundant near the head of a former glacial lake at 115 m elevation large adult salmon are concentrated in a sequence of death assemblages that include individuals with enlarged breeding teeth and worn caudal fins indicating migration nest digging and spawning prior to death the specimens were 4 yr old and 45 70 cm in total length similar in size to modern sockeye salmon not landlocked kokanee the fossils possess most of the characteristics of sockeye salmon oncorhynchus nerka but with several minor traits suggestive of pink salmon o gorbuscha this suggests the degree of divergence of these species at about 1 million yr ago when geological evidence indicates the salmon were deposited at the head of a proglacial lake impounded by the salmon springs advance of the puget lobe ice sheet surficial geology and topography record a complicated history of glacial damming and river diversion that implies incision of the modern gorge of the south fork skokomish river after deposition of the fossil bearing sediments 2007 university of washington all rights reserved

a holocene sedimentary record of tectonically influenced reduced channel mobility skokomish river delta washington state usa abstract at the skokomish river delta in washington state s puget lowland coseismic uplift and tilting trapped the river against a valley wall resulting in little to no channel migration for the last 1000 years the most recent earthquake occurred before ad 780 990 based on stratigraphic evidence such as sand blows and abrupt facies changes since the hypothesized tilting a 5 km long section of the river has not migrated laterally or avulsed resulting in reduced migration and a muddy intertidal flat that is 2 km wider in the east than on the west side of annas bay a ridge running perpendicular to the river may also have restricted channel mobility the ridge may be either the surface expression of a blind thrust fault or a relict uplifted and tilted shoreline the uplift and tilting of the delta can be ascribed to any of three nearby active fault zones of which the most likely based on the orientation of deformation is the saddle mountain fault zone which produced a surface rupture 1000 1300 years ago the delta has experienced submergence since the earthquake a forest that colonized an uplifted part of the delta about 800 1200 years ago was later submerged by at least 1 6 m and is now a brackish water marsh

climate variability and ice sheet dynamics during the last three glaciations a composite north atlantic record from dsdp site 609 and iodp site u1308 spans the past 300 000 years and shows that variability within the penultimate glaciation differed substantially from that of the surrounding two glaciations hematite stained grains exhibit similar repetitive down core variations within the marine isotope stage mis 8 and 4 2 intervals but little cyclic variability within the mis 6 section there is also no petrologic evidence in terms of detrital carbonate rich heinrich layers for surging of the laurentide ice sheet through the hudson strait during mis 6 rather very high background concentration of iceberg rafted debris ird indicates near continuous glacial meltwater input that likely increased thermohaline disruption sensitivity to relatively weak forcing events such as expanded sea ice over deepwater formation sites altered sub tropical precipitation patterns and antarctic warming during high orbital precession and low 65 n summer insolation appear related to high abundance of icelandic glass shards and southward sea ice expansion differing european and north american ice sheet configurations perhaps aided by larger variations in eccentricity leading to cooler summers may have contributed to the relative stability of the laurentide ice sheet in the hudson strait region during mis 6

origin and evolution of the seattle fault and seattle basin washington analysis of seismic reflection data reveals that the seattle basin washington is markedly asymmetric and consists of 9 10 km of eocene and younger deposits the basin began as a discrete geologic element in the late eocene 40 ma the result of a reorganization in regional fault geometry and kinematics in this reorganization dextral offset on the puget fault south east of seattle stepped eastward and the seattle fault began as a restraining transfer zone north vergent reverse or thrust faulting on the seattle fault forced flexural subsidence in the seattle basin to the north offset on the seattle fault and subsidence of the seattle basin have continued to the present

measured and predicted rates of sediment transport in storm conditions abstract owing to difficulties in obtaining measurements and to the vagaries of the weather at sea few field data exist pertaining to sediment mobilisation and transport in storm conditions consequently empirical formulae widely used to predict sediment transport in marine environments remain largely untested in extreme conditions in the present paper bedload transport rates estimated from measured rates of bedform migration and measured rates of suspended sediment transport have been compared with predictions from various empirical formulae rates of bedload transport inferred from measured rates of ripple migration are found to compare favourably with previous observations and with empirical predictions obtained using the bijker formula measured rates of total sediment transport are found to agree well with predictions from the soulsby formula results show that these formulae are able to predict accurately marine sediment transport in combined wave current conditions during a storm

models of rapid relative sea level change in washington and oregon usa much geological evidence points to repeated plate boundary earthquakes on the cas cadia subduction zone pacific northwest usa current land motions calculated using shortterm 100 yr tide gauge repeat levelling and other geodetic data record deformation during the present interseismic period these short term data form the basis of efforts to model longer term plate boundary deformation and assess seismic hazard in this region in this paper we use relative sea level rsl data from the last 4000 cal yr bp to examine four aspects of these plate boundary deformation models over several earthquake cycles rates of isostatic rebound the spatial pattern and magnitude of coseismic deformation and rates of interseismic strain accumulation age altitude plots of rsl data from a 300 km long string of sites stretching from copalis river central washington to alsea bay central oregon reveal a systematic northsouth decline in the rate of isostatic rebound equal to c 0 25 0 02 mm yr 1 100 krn high

experimental characterization of storm liquefaction deposits sequences abstract the collapse depressions in waters of the yellow river delta are the result of silty sediment liquefaction produced by storm waves the internal characteristics and formation process of the strata in collapse depressions were studied with consideration of re stratification caused by sediment liquefaction in coastal areas in wave flume experiments silty sediment collected from the yellow river delta was shaped into a model seabed the original uniform sediment stratum was re stratified and formed into a new structure characteristic of liquefied sediments fluctuating with wave movement wave action appears to cause silty sediment liquefaction liquefied sediment moved elliptically with wave action leading to granularity based deposit differentiation in situ to re form sedimentary strata this is probably the cause of collapse depressions in the yellow river delta based on these results and comparison with the stratum under the collapse depressions in the yellow river delta we propose that liquefaction deposits are responsible for the bottom to top sequence of graded bedding convolute bedding and parallel bedding

crustal earthquake triggering by pre historic great earthquakes on subduction zone thrusts triggering of earthquakes on upper plate faults during and shortly after recent great m 8 0 subduction thrust earthquakes raises concerns about earthquake triggering following cascadia subduction zone earthquakes of particular regard to cascadia was the previously noted but only qualitatively identified clustering of m 6 5 crustal earthquakes in the puget sound region between about 1200 900 cal years b p and the possibility that this was triggered by a great cascadia thrust subduction thrust earthquake and therefore portends future such clusters we confirm quantitatively the extraordinary nature of the puget sound region crustal earthquake clustering between 1200 900 cal years b p at least over the last 16 000 we conclude that this cluster was not triggered by the penultimate and possibly full margin great cascadia subduction thrust earthquake however we also show that the paleoseismic record for cascadia is consistent with conclusions of our companion study of the global modern record outside cascadia that m 8 6 subduction thrust events have a high probability of triggering at least one or more m 6 5 crustal earthquakes

vented sediments and tsunami deposits in the puget lowland washington differentiating sedimentary processes the sandy deposits produced by tsunamis and liquefaction share many sedimentary features and distinctions between the two are important in seismically active coastal zones both types of deposits are present in the wetlands bordering puget sound where one or more earthquakes about 1100 years ago caused both tsunami flooding and sediment venting this co occurrence allows an examination of the resulting deposits and a comparison with tsunami and liquefaction features of modern events vented sediments occur at four of five wetland field localities and tsunami deposits at two in comparison with tsunami deposits vented sediments in this study and from other studies tend to be thicker although they can be thin vented sediments also have more variable thickness at both outcrop and map scale are associated with injected dykes and contain clasts derived from underlying deposits further vented sediments tend to contain a greater variety of sedimentary structures and these structures vary laterally over metres tsunami deposits compared with vented sediments are commonly thinner fine and thin landward more consistently have more uniform thickness on outcrop and map scales and have the potential of containing coarser clasts up to boulders for both tsunami deposits and vented sediments the availability and grain size of source material condition the characteristics of the deposit in the cases presented in this paper both foraminifera and diatom assemblages within tsunami deposits and vented sediments consisted of brackish and marine species and no distinction between processes could be made based on microfossils in summary this study indicates a need for more careful analysis and mapping of coastal sediments associated with earthquakes to avoid misidentification of processes and misevaluation of hazards

sea level change and paleogeographic reconstructions southern vancouver island british columbia canada abstract forty eight new and previously published radiocarbon ages constrain deglacial and postglacial sea levels on southern vancouver island british columbia sea level fell rapidly from its high stand of about 75 m elevation just before 14 000 cal bp 12 000 radiocarbon yrs bp to below the present shoreline by 13 200 cal bp 11 400 radiocarbon years bp the sea fell below its present level 1000 years later in the central strait of georgia and 2000 years later in the northern strait of georgia reflecting regional differences in ice sheet retreat and downwasting direct observations only constrain the low stand to be below 11 m and above 40 m analysis of the crustal isostatic depression with equations utilizing exponential decay functions appropriate to the cascadia subduction zone however places the low stand at 30 5 m at about 11 200 cal bp 9800 bp the inferred low stand for southern vancouver island when compared to the sea level curve previously derived for the central strait of georgia to the northwest generates differential isostatic depression that is consistent with the expected crustal response between the two regions morphologic and sub bottom features previously interpreted to indicate a low stand of 50 to 65 m are re evaluated and found to be consistent with a low stand of 30 5 m submarine banks in eastern juan de fuca strait were emergent at the time of the low stand but marine passages persisted between southern vancouver island and the mainland the crustal uplift presently occurring in response to the late pleistocene collapse of the southwestern sector of the cordilleran ice sheet amounts to about 0 1 mm yr the small glacial isostatic adjustment rate is a consequence of low viscosity mantle in this tectonically active region

climatic influences on profile concavity and river incision 1 longitudinal profiles of alluvial and bedrock rivers are typically concave up and the precise shape of their concavity is known to integrate tectonic climatic and channel grain size distribution factors we isolate climatic hydrologic effects on profile concavity through a spatial analysis of large watersheds with mixed bedrock alluvial trunk channels spanning a steep climatic hydrologic gradient in a tectonically stable landscape forty watersheds on the eastern american high plains were selected to minimize variability in base level relief vegetation rock type and drainage area we calculate stream concavity by two complementary methods an area normalized stream concavity index sci and the slope of a line regressed through log log plot of channel slope and basin area the sci and covary more importantly a positive correlation exists between profile concavity and climatic hydrologic factors such as precipitation intensity and peak annual discharge however modeled profile steepness has no correlation to climate or watershed hydrology we conclude that in tectonically stable settings higher intensity rainfall and greater mean annual precipitation lead to more concave profiles we do not have data to know if the concavity changes reflect primarily bedrock or alluvial grain size processes but generally a doubling of rainfall intensity on the high plains leads to a tripling in concavity manifest as tens of meters of incision such climatically influenced profile concavity could explain some of the often cited late cenozoic incision and increase in local relief for the high plains and rocky mountains traditionally ascribed to tectonics

evidence for eight great earthquake subsidence events detected with ground penetrating radar willapa barrier washington a new approach to detect holocene subduction zone earthquakes combines the results from ground penetrating radar gpr vibracores and accelerator mass spectrometry ams dates from a barrier spit located west of willapa bay southwest washington gpr data show a 10 m thick facies of beach sand within which we identify and vibracores confirm beach parallel wave eroded buried scarps mantled with multiple beds of magnetite the eight gpr detected buried scarps are interpreted to be eroded by minor transgressions caused by instantaneous barrier subsidence during earthquakes associated with the juan de fuca plate subducting under the north american plate of these scarps four have been ams dated at 300 1110 2540 and 4250 radiocarbon yr b p no datable material has yet been found for the other four radar detected scarps but we interpolate and extrapolate dates of 1800 3400 5000 and 5800 yr b p

finding concealed active faults extending the southern whidbey island fault across the puget lowland washington 1 the southern whidbey island fault zone swif as previously mapped using borehole data potential field anomalies and marine seismic reflection surveys consists of three subparallel northwest trending strands extending 100 km from near vancouver island to the northern puget lowland east of puget sound the swif makes landfall between the cities of seattle and everett but is concealed beneath a thick mantle of young glacial deposits and vegetation a 20 km wide northwest trending swath of subparallel low amplitude aeromagnetic anomalies crosses this region of the puget lowland and is on strike with the swif the most prominent aeromagnetic anomaly the cottage lake lineament extends at least 18 km and lies approximately on strike with the swif on whidbey island subtle scarps and topographic lineaments on pleistocene surfaces visible on high resolution lidar topography at a number of locations along the swif lie on or near these magnetic anomalies in the field scarps exhibit northeast side up and vertical relief of 1 to 5 m excavations across several lidar scarps lying on or near magnetic anomalies show evidence for multiple folding and faulting events since deglaciation most likely above buried reverse oblique faults excavations in areas away from magnetic anomalies do not show evidence of tectonic deformation in total paleoseismological evidence suggests that the swif produced at least four earthquakes since deglaciation about 16 400 years ago the most recent less than 2700 years ago

gradient analysis of diatom assemblages in a puget sound salt marsh can such assemblages be used for quantitative paleoecological reconstructions abstract taphonomy is important to coastal paleoecologists because processes acting on diatom thanocoenoses tend to work towards obscuring original ecological relationships between diatom assemblages and the environment the purpose of this paper is to briefly describe diatom taphonomy and present a method for quantitative reconstruction of environmental parameters from salt marsh diatom assemblages the main hypothesis for this study is that major environmental and taphonomic processes e g tides act in predictable ways to distribute living and dead diatoms along environmental gradients to test this hypothesis a modern transect was established across a large salt marsh in southwestern puget sound for the purpose of determining modern species environment gradients and calibrating species assemblages to environmental variables canonical correspondence analysis cca relates modern species assemblages to environmental gradients and weighted averaging calibration is used to develop transfer functions for predicting environmental information cca showed that the effect of salinity and elevation on the species distributions is significant indicating that environmental processes control the distribution of sedimentary diatoms across the salt marsh surface in predictable ways salinity was strongly correlated with cca axis 1 and elevation with axis 2 the calibration results indicate that although mixing of allochthonous and autochthonous diatoms does occur salt marsh diatom assemblages reflect major environmental gradients in puget sound salt marshes and can be effectively used for quantitative reconstructions of former environmental conditions

causes of river avulsion insights from the late holocene avulsion history of the mississippi river u s a abstract the emphasis on gradient advantages in studies of avulsion is misleading while gradient advantages are necessary for an avulsion to occur the late holocene avulsion history of the mississippi river in louisiana suggests that factors such as substrate composition and floodplain channel distributions are more important cross valley to down valley slope ratios of the modern floodplain range from 16 to 110 and are typically 30 the slope ratio is 35 at the location of the mississippi atchafalaya diversion old river yet slope ratios are 83 to 110 immediately upvalley of old river all values of mississippi river floodplain slope ratios are significantly larger than values of avulsion threshold calculated by numerical models shallow floodplain cores 14c dating of organic remains and geologic mapping show that the mississippi river has avulsed only four times over the past 5 ky in the southern lower mississippi valley lmv gradient advantages are widespread yet avulsions are rare these observations indicate that factors other than gradient advantage control mississippi river avulsion several examples of mississippi and red river avulsion by channel reoccupation support the idea that channel distributions and substrate compositions are primary influences on avulsion incipient mississippi river avulsion and development of the atchafalaya river involved reoccupation of abandoned mississippi river channels and a red river crevasse splay complex the modern atchafalaya river also incises buried mississippi river channel belt sands abandoned channel belts and crevasse splay complexes consist of sandy substrates that facilitate scour and the development of channels capable of capturing the mississippi river abandoned channels provide ready made conduits for mississippi river flow that can efficiently develop into avulsive channels multi storied sheet sandstones in ancient fluvial deposits may provide additional support for the idea that erodible substrates and floodplain channel distributions are critical influences on avulsion these features record episodic reoccupation of channel belts which at least in some cases may simply reflect successive avulsions rather than major changes in aggradation rate or extrabasinal factors such as climate

rupture models for the a d 900 930 seattle fault earthquake from uplifted shorelines a major earthquake on the seattle fault washington ca a d 900 930 was first inferred from uplifted shorelines and tsunami deposits despite follow up geophysical and geological investigations the rupture parameters of the earthquake and the geometry of the fault are uncertain here we estimate the fault geometry slip direction and magnitude of the earthquake by modeling shoreline elevation change the best fitting model geometry is a reverse fault with a shallow roof ramp consisting of at least two back thrusts the best fitting rupture is a sw ne oblique reverse slip with horizontal shortening of 15 m rupture depth of 12 5 km and magnitude mw 7 5

differentiating the effects of logging river engineering and hydropower dams on flooding in the skokomish river washington usa abstract a decades long progressive loss of channel capacity in the skokomish river a 622 km2 basin draining the southeast olympic mountains of washington state has caused increasing flooding with severe consequences to endangered salmon runs infrastructure and private property to differentiate among multiple potential drivers of the capacity loss we analyze the geomorphic evidence for the potential effects of flow regulation by two dams constituting the cushman hydroelectric project which began regulating flow in the river s north fork in 1925 and diverting water out of the basin in 1930 sediment production from mid twentieth century logging in the river s south fork basin and twentieth century river engineering in the mainstem bankfull channel capacity in the mainstem has steadily declined since about 1940 from 370 m3 s 1 to

first quantitative test of alluvial stratigraphic models southern rio grande rift new mexico since 1978 the results of computational architectural models have been widely used to aid interpretation of ancient alluvial successions here we present the first quantitative test of such models we parameterize variables from field and magnetostratigraphic data collected from the well exposed pliocene pleistocene camp rice and palomas formations of the rio grande rift in south central new mexico computational runs establish that the lab leeder allen and bridge model correctly predicts the gross architectural patterns of ancestral axial rio grande half grabens and full grabens convergence of tectonic subsidence rate and mean sedimentation rate over the studied interval suggests that the dynamic basis of the models is correct i e it is the tectonic drawdown of axially supplied sediment that controls the net preservation potential of alluvial successions

glaciofluvial infilling and scour of the puget lowland washington during ice sheet glaciation the puget lobe the southwesternmost extension of the cordilleran ice sheet last advanced into the puget lowland of western washington at about 15 ka the advancing ice sheet deposited voluminous sediment on a prograding proglacial outwash plain that extended from the olympic mountains to the cascade range herein recognized as the great lowland fill subsequent overrunning by the ice sheet excavated deep linear troughs now occupied by the large lakes and marine waters of puget sound excavation of these troughs and valleys of the puget lowland required the net transport of about 1000 km3 of sediment almost entirely during ice occupation and primarily by subglacial water these landforms of glaciofluvial deposition and erosion define the modern landscape here emphasizing the importance of these processes in the region s geomorphology

the a d 900 930 seattle fault zone earthquake with a wider coseismic rupture patch and postseismic submergence inferences from new sedimentary evidence stratigraphic evidence for coseismic uplift a tsunami and a sandy debris flow linked to the a d 900 930 seattle fault zone earthquake and subsequent submergence is present at gorst at the terminus of sinclair inlet washington this study indicates that at least 3 m of uplift preceded a tsunami followed by a sandy debris flow though the seattle and tacoma fault zones ruptured within the error of ages of the tsunami deposit model simulations indicate the seattle fault generates an order of magnitude larger tsunami in the vicinity of the field area than the tacoma fault and is the more likely generator of the tsunami simulations indicate amplitude from a seattle fault zone generated wave train was 4 5 m and stratigraphy shows the tsunami left a sandy deposit soft sediment deformation narrows the time window for the debris flow to the hours to months after the tsunami slope failure in unconsolidated glacial sands likely initiated a debris flow that surged at least 2 km down gorst creek valley and left a more than 40 cm thick deposit along the creek and in the wetlands submergence of a thuja plicata western red cedar swamp into the intertidal zone indicates at least 1 5 m of submergence in the last 1100 years this submergence indicates uplift on nearby marine terraces associated with the seattle fault zone was likely higher and the a d 900 930 earthquake was potentially larger than previously recognized

gps deformation in a region of high crustal seismicity n cascadia forearc we estimate the rate of crustal deformation in the central and northern cascadia forearc based on a combination of existing global positioning system gps velocity data along the cascadia subduction zone gps strain rates and velocities show that the northwestern washington southwestern british columbia region is currently shortening at 3 3 5 mm yr 31 in a n s direction in good agreement with inference from crustal earthquake statistics on the longterm the shortening rate is 5 6 mm yr 31 providing that the subduction related interseismic loading of the margin is purely elastic compared to the velocity of the oregon forearc with respect to north america v 7m m yr 31 this indicates that most of the forearc motion is accommodated in the puget georgia basin area corresponding to the main concentration of crustal seismicity the difference between the current and long term shortening rates may be taken up during subduction megathrust earthquakes thus these events could produce a sudden increase of n s compression in the puget sound region and could trigger major seattle fault type crustal earthquakes published by elsevier science b v

abrupt uplift within the past 1700 years at southern puget sound washington shorelines rose as much as 7 meters along southern puget sound and hood canal between 500 and 1700 years ago evidence for this uplift consists of elevated wave cut shore platforms near seattle and emerged peat covered tidal flats as much as 60 kilometers to the southwest the uplift was too rapid for waves to leave intermediate shorelines on even the best preserved platform the tidal flats also emerged abruptly they changed into freshwater swamps and meadows without first becoming tidal marshes where uplift was greatest it adjoined an inferred fault that crosses puget sound at seattle and it probably accompanied reverse slip on that fault 1000 to 1100 years ago the uplift and probable fault slip show that the crust of the north america plate contains potential sources of damaging earthquakes in the puget sound region

radiocarbon age constraints on rates of advance and retreat of the puget lobe of the cordilleran ice sheet during the last glaciation abstract calibrated radiocarbon dates of organic matter below and above till of the last fraser glaciation provide limiting ages that constrain the chronology and duration of the last advance retreat cycle of the puget lobe in the central and southeastern puget lowland seven dates for wood near the top of a thick proglacial delta have a weighted mean age of 17 420 90 cal yr b p which is the closest limiting age for arrival of the glacier near the latitude of seattle a time distance curve constructed along a flowline extending south from southwestern british columbia to the central puget lowland implies an average glacier advance rate of ca 135 m yr the glacier terminus reached its southernmost limit ca 16 950 yr ago and likely remained there for ca 100 yr in the vicinity of seattle where the glacier reached a maximum thickness of 1000 m ice covered the landscape for ca 1020 yr postglacial dates constraining the timing of ice retreat in the central lowland are as old as 16 420 cal yr b p and show that the terminus had retreated to the northern limit of the lowland within three to four centuries after the glacial maximum the average rate of retreat was about twice the rate of advance and was enhanced by rapid calving recession along flowline sectors where the glacier front crossed deep proglacial lakes

evidence for earthquake induced subsidence about 1100 yr ago in coastal marshes of southern puget sound washington buried forest and high marsh soils indicate abrupt changes in relative sea level at four coastal localities in southern puget sound at little skookum inlet and red salmon creek douglas fir stumps in growth position are buried by salt marsh peat at localities along mcallister creek and the nisqually river high marsh soils are buried by tidal flat mud localized liquefaction coincided with submergence of the high marsh soil at mcallister creek dramatic changes in seed and diatom assemblages across these contacts confirm rapid submergence at little skookum inlet and red salmon creek salt marsh peat immediately above a buried forest soil contains diatoms indicative of low marsh and tidal flat environments at mcallister creek and nisqually river low marsh and tidal flat diatoms are abundant in laminated mud directly over high marsh peat inferences from modern analogs indicate at least 1 m of subsidence at each site and possibly up to 3 m at skookum inlet abrupt burial of lowland soils in southern puget sound is best explained by coseismic subsidence some of the submergence may be the result of coseismic compaction and postearthquake settlement widespread buried soils large amounts of subsidence coeval submergence across a wide area and ground shaking at the time of subsidence all point to a large earthquake between 1150 and 1010 cal yr b p in southern puget sound as the most likely cause of subsidence

modeling fluvial incision and transient landscape evolution influence of dynamic channel adjustment 1 channel geometry exerts a fundamental control on fluvial processes recent work has shown that bedrock channel width depends on a number of parameters including channel slope and is not solely a function of drainage area as is commonly assumed the present work represents the first attempt to investigate the consequences of dynamic gradient sensitive channel adjustment for drainage basin evolution we use the channel hillslope integrated landscape development child model to analyze the response of a catchment to a given tectonic perturbation using as a template the topography of a well documented catchment in the footwall of an active normal fault in the apennines italy that is known to be undergoing a transient response to tectonic forcing we show that the observed transient response can be reproduced to first order with a simple detachment limited fluvial incision law transient landscape is characterized by gentler gradients and a shorter response time when dynamic channel adjustment is allowed the differences in predicted channel geometry between the static case width dependent solely on upstream area and dynamic case width dependent on both drainage area and channel slope lead to contrasting landscape morphologies when integrated at the scale of a whole catchment particularly in presence of strong tilting and or pronounced slip rate acceleration our results emphasize the importance of channel width in controlling fluvial processes and landscape evolution they stress the need for using a dynamic hydraulic scaling law when modeling landscape evolution particularly when the relative uplift field is nonuniform

sediment transport part iii bed forms and alluvial roughness a method is presented that makes the classification of bed forms the prediction of the bed form dimensions and the effective hydraulic roughness of the bed forms feasible the proposed relationships are based on the analysis of reliable flume and field data a verification analysis using about 1 500 alternative reliable flume and field data shows good results in predicting the hydraulic roughness friction factor for field conditions the proposed method yields considerably better results than previously proposed methods which are reviewed here the proposed method has also been used to predict the flow depth and the total bed material load

oversampling of sedimentary series collected by giant piston corer evidence and corrections based on 3 5 khz chirp profiles 1 the depth scale accuracy of marine sedimentary series collected by coring is of key importance for the precise calculation of sedimentation rates and fluxes for three giant piston cores collected during the interpole md99 114 international marine past global changes study images v cruise md99 2227 md99 2246 and md99 2251 the 3 5 khz chirp profiles recorded on board are compared to synthetic seismograms computed from physical property logs measured on cores in each case the perfect match of main deep reflectors requires a significant upward shift of the water sediment w s interface in the synthetic seismograms with respect to the 3 5 khz profiles since no drastic perturbation of the physical property logs is observed this upward shift is interpreted as resulting from a significant sediment oversampling in the upper part of the cores the affected depth intervals are consistent with the thickness of the perturbed zones observed in penetrometry and anisotropy of magnetic susceptibility records 10 15 m to retrieve the true in situ sediment thickness a linear depth correction is applied between consecutive acoustic reflectors to achieve a perfect match between the synthetic seismogram and the corresponding 3 5 khz profiles depth correction laws amount of material excess as a function of initial depth are deduced from this resynchronization procedure first estimations of upper core oversampling rates range from 30 core md99 2227 to 37 core md99 2246 moreover we observe that some undersampling may also exist in the lower part of the sediment cores

early holocene history of the baltic sea as reflected in coastal sediments in blekinge southeastern sweden integrated palaeoecological studies of two fiord sediment sequences in the province of blekinge se sweden covering the time span 11 000 5000 cal bp reveal the timing and the environment for the ancylus lake littorina sea transition 9800 8500 cal bp the first ingression of saline water into the baltic sea through the danish straits occurred earlier than formerly assumed new evidence particularly mineral magnetic and palaeobotanical analyses demonstrate that on the general trend of the eustatically caused littorina transgression several minor fluctuations of the water level can be identified between 8500 and 5000 cal years bp a distinct regression phase around 8 100 cal bp is correlated with the greenland ice core cold event dated to 8200 ice core years bp this is described as a regional climatic catastrophe for the baltic sea region the coastal stratigraphy is compared with the offshore stratigraphy earlier studied a tentative shore displacement curve for early and middle holocene is presented

the legacy of pleistocene glaciation and the organization of lowland alluvial process domains in the puget sound region article i nfo alluvial rivers of the eastern puget lowland a landscape shaped by scour and fill from the cordilleran ice sheet continue to respond to patterns of deposition and scour by the last glacial age ice sheet 18 000 years after deglaciation topography revealed by valley cross sections created from high resolution lidar digital elevation models shows that rivers are aggrading in valleys eroded by subglacial runoff and degrading in valleys incised by rivers post glaciation slope area analysis of river profiles shows that profile concavity varies systematically between river segments in the two valley contexts concavity indices in mountain headwaters 0 3b b0 9 compare to those of many world rivers 0 2b b1 0 but in the lowlands these indices differ between valleys created by subglacial fluvial erosion 5b b45 and post glacially incised river valleys that grade to base levels set by these relict glacial valleys or by post glacial sea levels 1b b7 dramatic differences in river pattern landforms and dynamics occur in valleys having contrasting aggrading vs degrading and incomplete responses to pleistocene glaciation creating discrete valley scale hetero geneities in fluvial process domains along and between rivers these results point to the importance of valley scale organization of alluvial process domains along and between rivers having profiles remaining in disequilibrium from pleistocene glaciation they also point to the potential usefulness of slope area analysis of longitudinal profiles in distinguishing among different river valley process domains in lowland alluvial landscapes

sedimentary processes bedforms and facies associated with a coastal headland portland bill southern uk this investigation presents new findings on the sedimentary processes and deposits associated with a coastal headland in a mixed tide wave setting using data compilation bathymetric and sediment distribution maps collected field data side scan sonar and seabed sampling and sand transport modelling sand transport pathways are described a on the basis of coupled system seabed morphology sand distribution and b from bed shear stress and medium grained sand transport rate simulations the presence of a sequence of sedimentary deposits associated with a complex suite of bedforms and sedimentary facies within an overall framework of limited sediment supply represents a gradient in shear stress and sand transport towards the headland these sequences are observed on both sides of portland bill tending towards a symmetrical distribution the sedimentary facies distribution is combined with sand transport rates and maximum bed shear stress distribution to suggest a conceptual model for sand dispersal and deposit formation around headlands sand dispersal can be explained in terms of a headland associated eddy bedload convergent zone concept maximum bed shear stress is observed at the tip of the headland and is associated with bedrock exposed on the seabed the sequence of sedimentary deposits away from the headland is sandbanks shambles and portland banks sand gravel flats sand shoals adamant and west shoals and rippled sand sheets the banks lie in an area of very high bed shear stress u 0 08 m s 1 this is greater than that for other tidal sandbanks not associated with headlands bank formation is the result of the strong convergent transport component enhanced by the development of transient headland eddies the sandbanks are to some extent also morphologically controlled i e the portland bank is affected by the deep bathymetry to the west side of portland bill the principal characteristic of headland associated eddy bedload convergent zones is the development of bed shear stress convergent zones on both sides of the headland two conceptually distinct regions of sedimentary processes associated with the coastal headlands are recognised a an inner zone with increasing gradients in sand transport and bed shear stress towards the headland and b an outer zone in which sand transport is away from the headland associated with a decrease in the bed shear stress these zones merge into a bed shear stress sand bedload transport convergent zone which enhances the formation of sandbanks around headlands thus headland associated sedimentary deposits are a complex system compared with the occurrence of isolated sandbanks described elsewhere the identification of a sequence of deposits related to and extending much farther from the headland than previously supposed demonstrates that the tidal stirring concept of headland associated sandbanks may explain the formation of headland associated sandbanks however it ignores the presence of a suite of sedimentary deposits around such headlands the conceptual model proposed here provides a sedimentological perspective on the formation and occurrence of headland associated deposits including sandbanks

sediment transport by waves and currents a bed load model based on a generalization of bagnold s 1954 constitutive equations together with the assumption of similarity profiles for velocity and concentration was proposed for sediment transport by waves by sleath 1994 this model is now extended to wave current flows and applied to three different situations a oscillatory flows with superimposed currents b net transport produced by progressive waves over a flat horizontal bed and c longshore transport induced by waves approaching a beach in all three cases the model gives reasonable agreement with experiment in the case of longshore transport the model produces almost the same formula as that of the coastal engineering research center 1977 apart from additional terms for density and grain size

video based observations of nearshore sand ripples and ripple migration 1 observations of o 1 m length and o 0 1 m height sand ripples at waimea bay a steep slope 0 05 pocket beach on the north shore of oahu hawaii are presented time series of ripple patterns over a 900 m2 section of the nearshore in depths of 1 2 m are obtained using time averaged video images from an argus station overlooking the bay ripples are detected during weak wave conditions in the summer or between winter swell events the ripple field exhibits narrow band wave number structure with ripple crests oriented parallel to the shoreline the ripple wavelengths vary with wave orbital displacements but they are shorter than predicted by orbital vortex ripple scaling relationships a new suspension limited model smith and wiberg 2006 traykovski 2006 in which the suborbital ripple wavelengths vary with wave period appears to describe well the observed ripple wavelength scaling lagged correlations between sequential argus images reveal area average ripple migration rates ranging from 3 3 m day 1 offshore to 4 5 m day 1 the corresponding estimated sediment transport ranges from 0 3 m3 m 1 day 1 to 0 5 m3 m 1 day 1 similar to previous estimates of cross shore transport based on observed volume changes at the subaerial beach this suggests that the recovery of beach sand following major swell driven erosion events may be accomplished in part by the shoreward migration of seabed ripples

influence of steady base level rise on channel mobility shoreline migration and scaling properties of a cohesive experimental delta 1 here we describe results from an alluvial delta physical experiment with and without steady base level rise using a unique cohesive sediment mixture that promotes the development of persistent channels and a rugose shoreline we quantitatively characterize channel network properties as a function of base level rise in a distributary system that reproduces many aspects of the geometry of natural deltas analysis of the experimental data shows clear dynamical differences between the predominantly progadational and aggradational phases of the experiment the experiment was conducted in two phases a first in which the delta prograded into standing water of constant depth in the absence of base level rise and a second during which steady base level rise was imposed on the system forcing a twofold increase in topset aggradation due to greater sediment retention in the fluvial reach the shift in sediment mass balance to enhanced fluvial deposition in the second phase caused channel network mobility to increase reducing the autogenic channel time scale from 23 5 to 12 5 h and supporting a positive correlation between deposition and channel avulsion frequency an independent shoreline time scale that characterizes the dominant time over which shoreline regression is persistent closely correlates with measurements of the channel network 28 3 h during fan progradation and 9 5 h during fan aggradation these metrics suggest a strong coupling between channel network and shoreline kinematics and a more active fluvial surface during fan aggradation by a factor of 2 to 3 similar to the increase in aggradation rate spatial scaling of shoreline roughness reveals that maximum shoreline variability is set by the scale of distributary lobes strong coupling exists between delta growth and shoreline geometry during progradation during aggradation however shoreline variability is not solely due to distributary lobe growth but is also set by shoreline transgression over inactive portions of the delta illustrating a decoupling between fan kinematics and fan geometry this decoupling together with the matched increase in channel network mobility and fluvial aggradation suggest the stratigraphic architecture may not be a strong geometric signal of different fluvial surface conditions either

geologic evidence of earthquakes at the snohomish delta washington in the past 1200 yr exposed channel banks along distributaries of the lower snohomish delta in the puget lowland of washington reveal evidence of at least three episodes of liquefaction at least one event of abrupt subsidence and at least one tsunami since ca a d 800 the 45 measured stratigraphic sections consist mostly of 2 4 m of olivegray intertidal mud containing abundant marsh plant rhizomes the most distinctive stratigraphic unit is a couplet comprising a 0 523 cm thick laminated fining upward tsunami laid sand bed overlain by 2210 cm of gray clay we correlated the couplet which is generally 2 m below the modern marsh surface across an 20 km2 area sand dikes and sand filled cracks to 1 m wide which terminate upward at the couplet and sand volcanoes preserved at the level of the sand bed record liquefaction at the same time as couplet deposition differences in the type and abundance of marsh plant rhizomes across the couplet horizon as well as the gray clay layer suggest that compaction during this liquefaction led to abrupt local lowering of the marsh surface by as much as 50 75 cm radiocarbon ages show that the tsunami and liquefaction date from ca a d 800 to 980 similar to the age of a large earthquake on the seattle fault 50 km to the south we have found evidence for at least two and possibly as many as five other earthquakes in the measured sections at two or more stratigraphic levels above the couplet sand dikes locally feed sand volcanoes radiocarbon ages and stratigraphic position gov suggest that one set of these dikes formed ca a d 910 990 radiocarbon ages on a younger set indicate a limiting maximum age of a d 1400 1640 we also interpret a sharp lithologic change from olive gray rhizome rich mud to grayer rhizome poor mud 1 m above the couplet to indicate a second abrupt lowering of the marsh surface during an earthquake ca a d 1040 1400 but no conclusive liquefaction structures have been identified at this horizon two distinctive coarse sand laminae 30 80 cm below the couplet may record tsunamis older than a d 800 thus study shows that in the past 1200 yr this part of washington s puget lowland has been subjected to stronger ground shaking than in historic times since ca 1870

storm influence on the burial of objects in a shallow sandy shelf environment abstract for rapid assessments of occurrences of sea mines or objects and probability modelling of object burial mechanisms knowledge is needed on sediment processes under a variety of hydro meteorological conditions one approach is to use test mines that record burial mechanisms over longer time periods a burial recording mine brm was deployed in the belgian part of the north sea in water depths of 7 to 12 m the area is predominantly sandy with a continuous spectrum of small to medium and large dunes three months of data were recorded and allowed monitoring of small scale seabed variation this was correlated to ruling current and wave conditions during the recording period two short intense storms affected the area the burial behaviour of the cylindrical object revealed that the depth related wave energy decay rate immediately after the storm was the main factor causing sedimentation moreover sequential storms caused a cascade effect with the object being vertically relocated in a deeper position the results gave insight into the processes and the timing of erosion and sedimentation during and post storm providing more efficient strategies for the detection of missing objects results are relevant to assess storm impact on any man made object at sea

analysis and modelling of gravity and piston coring based on soil mechanics the effects of gravity and piston corers on the dimensional accuracy of marine sediment cores is analysed using principles of soil mechanics a model for the coring process is built around the feedback that arises and develops between the core barrel and the sampled sediment this model for sediment response is applied to different hypothetical coring scenarios which are then compared to real examples providing insights into the specific effects of each sampling method and the development of these effects down core four cores from a single location on the iberian margin are found to contain stratigraphically intact successions that differ in length by a factor of up to 2 7 due solely to the different effects of each coring method these dimensional discrepancies are attributed to the combined effects of over sampling in the upper portions of the piston cores due to cable rebound causing upward piston acceleration and under sampling dominant in the basal portions of the open barrel gravity type cores it is suggested that heavier piston corers deployed on longer lighter cables are prone to greater over sampling ratios over longer stratigraphic intervals due to the increased likelihood and extent of cable rebound cable rebound may also give rise to double penetration of gravity corers resulting in repeated stratigraphic intervals knowledge of the dimensional accuracy of marine sediment cores is essential to an evaluation of past sedimentation rates and hence interpretations of past depositional processes it is therefore essential that we recognise the sampling effects of each coring method and their variability down core lest coring artefacts be interpreted as sedimentary signals different core types may be more suited to different palaeoceanographic investigations hence failing the development of a practical cable deployed recoilless piston corer a combination of a variety of core types will permit the best acquisition of the in situ stratigraphic truth our results suggest that a large diameter dc 20 30 cm square barrel gravity corer for the top 10 12 m combined with a cylindrical piston corer below 10 m may provide the least deformed material

a review of the history of the baltic sea 13 0 8 0 ka bp abstract the dynamic history of the baltic sea during the millennia following the last deglaciation has been one of the main topics for many generations of quaternary geologists around the baltic sea based on the present state of knowledge and certain hypotheses a model for the development during the baltic ice lake yoldia sea and ancylus lake stages are presented the oresund strait was the threshold of the initial stage of the baltic ice lake and was eroded down to bedrock as a result of the isostatic uplift the emerging threshold forced the baltic ice lake to rise above sea level at ca 12 0 ka bp this gradual up damming ended at ca 11 2 ka bp when the large glacial lake was lowered 5 10m by possible subglacial drainage at mt billingen a glacial readvance during the younger dryas ended a ca 400 year long land bridge between sweden and the continent by blocking the former drainage route once again the baltic ice lake had to rise above sea level to be drained over the oresund strait at ca 10 5 ka bp a gradual ice recession began and 200 years later when the receding ice sheet could not withhold the up dammed water masses the final drainage of the baltic ice lake occurred which rapidly lowered the water level within the baltic basin with ca 25 m and ended the baltic ice lake stage the next stage the yoldia sea was characterized by a complex pattern of relative sea level changes with large differences within the baltic basin a very restricted baltic sea in the south and thus an extensive landbridge at ca 9 9 ka bp a short 100 200 years saline ingression is seen in the baltic sediment records from stockholm in the north to the southernmost parts of the yoldia sea the gradually shallower strait in south central sweden the narke strait ended the saline influence 300 400 years later the two remaining outlets west of lake vanern gota alv and otteid steinselva had become too shallow to swallow the outflowing yoldia sea waters at this stage the baltic lake vanern level could thus not fall in pace with the relative sea level fall outside the outlet areas this was the isolation of lake vanern and the baltic from the sea and the beginning of the ancylus lake since the water depth of the larger gota alv outlet had to be more or less maintained the ancylus lake level had to rise in pace with the uplift of the outlet region this caused a significant and rapid transgression 10 30 m in ca 300 years in the southern baltic which flooded large areas with recently immigrated pine forests since the oresund strait during the yoldia sea stage had been uplifted more than southerly areas the ancylus transgression ended with a new drainage pathway at ca 9 2 ka bp through the darss sill area in the southern baltic and northwards through the store belt strait this so called dana river had cut off the former large land bridge the quaternary deposits of this new threshold were eroded and a fairly rapid regression set in at ca 9 0 ka bp the dana river had eroded down to the sea level which isolated lake vanern from the ancylus lake and created a land bridge between southern sweden and northwards ca 800 years later when the sea level rose above the oresund threshold marine water could enter the baltic and at ca 8 0 ka bp brackish water characterized the southern baltic this marks the end of the ancylus lake

geodetic evidence for active landward tilting of the oregon and washington coastal ranges nine leveling routes that extend inland from near the coast of oregon and washington indicate consistent landward tilting of the 600 km long coastal ranges at about 3 10 8 rad yr 1 analysis of tide gauge observations indicates tilting with roughly the same magnitude and sense as the leveling measurements these short term tilt rates 10 80 yr are comparable with longer term rates 100 000 yr deduced from tilted marine terraces contemporary landward tilting is interpreted to result from continuing subduction of the juan de fuca plate beneath north america the similarity between long and short term deformation suggests that present day subduction is occurring via aseismic creep as hypothesized by ando and balazs 1979 however recent measurements of horizontal deformation in northwest washington which have been interpreted to indicate elastic strain accumulation appear to be incompatible with aseismic subduction additional releveling observations along the oregon routes last observed in 1941 and further studies of late pleistocene deformation along the coastal region of oregon and washington could help determine present day tectonics and assess the risk of large thrust earthquakes in this area

bedform contributions to cross shore sediment transport on a dissipative beach abstract field measurements of hydrodynamics suspended sediment transport rates and bedform sediment transport rates were made in the intertidal section of a dissipative sandy beach d50 0 26 mm slope 1 80 at perranporth uk pressure transducers acoustic doppler velocimeters optical backscatter sensors and an acoustic sand ripple profiler were deployed for 12 tides measuring in a range of wave heights from 0 5 to 2 2 m water depths from 1 to 6 m and in current strengths up to 0 4 m s data were analysed in terms of the distance to shore x normalised by the surf zone width xs and spanned the region 0 4 1 5 the fractional contribution of the shoreward directed bedform transport to the total absolute transport was up to 100 and occurred broadly in the region of the breakpoint 0 5

timing and east west correlation of south swedish ice marginal lines during the late weichselian abstract the retreat of the late weichselian ice sheet over the southern part of sweden is marked along the southwest coast by distinct marginal moraine ridges their timing can directly and indirectly be assessed based on a number of radiocarbon dates and pollen stratigraphic investigations on lake sediment sequences adjacent to the ice marginal lines along the southeastern side of the peninsula the ice recession has been reconstructed based on a combination of clay varve chronology pollen and radiocarbon stratigraphy a morphological correlation of ice marginal lines between the west and east coast is problematic since the distinct west coast moraines cannot be followed through the central part of the peninsula towards the east coast this paper is an attempt to reconstruct an age equivalent west east extension of the ice recession lines on the basis of existing data sets for our correlation we use calibrated radiocarbon ages for ice marginal deposits on the west coast and compare these with a partly radiocarbon dated clay varve chronology on the east coast we conclude that the two oldest moraines on the west coast formed at 18 000 16 000 and 15 400 14 500 cal yr bp respectively during the following rapid deglaciation which may have coincided with the beginning of the bolling pollen zone large parts of southernmost sweden became ice free except for higher elevated areas where stagnant ice remained for another 400 500 yr a best guess is that the formation of the next younger ice marginal lines may have occurred at 14 400 14 200 14 200 and 13 400 cal yr bp and during the younger dryas cold event

sediment and rock strength controls on river incision into bedrock recent theoretical investigations suggest that the rate of river incision into bedrock depends nonlinearly on sediment supply challenging the common assumption that incision rate is simply proportional to stream power our measurements from laboratory abrasion mills support the hypothesis that sediment promotes erosion at low supply rates by providing tools for abrasion but inhibits erosion at high supply rates by burying underlying bedrock beneath transient deposits maximum erosion rates occur at a critical level of coarse grained sediment supply where the bedrock is only partially exposed fine grained sediments provide poor abrasive tools for lowering bedrock river beds because they tend to travel in suspension experiments also reveal that rock resistance to fluvial erosion scales with the square of rock tensile strength our results suggest that spatial and temporal variations in the extent of bedrock exposure provide incising rivers with a previously unrecognized degree of freedom in adjusting to changes in rock uplift rate and climate furthermore we conclude that the grain size distribution of sediment supplied by hillslopes to the channel network is a fundamental control on bedrock channel gradients and topographic relief

tectonic geomorphology of the san andreas fault zone in the southern indio hills coachella valley california geomorphic investigation of the san andreas fault zone in the indio hills indicates many tectonically produced landforms including beheaded streams right lateral deflected and offset streams sags shutter ridges pressure ridges and fault scarps near biskra palms an alluvial fan pediment complex has an apparent cumulative offset of about 0 7 km along the mission creek fault zone north branch san andreas fault many of the tectonic landforms as well as the fracture pattern that has developed during the pleistocene are explainable by simple shear or uplift associated with a small left bend in the main trace of the mission creek fault the ratio of vertical to horizontal displacement in the vicinity of the bend is about 0 04 exposed in pushawalla canyon 5 km northwest of the alluvial fan pediment complex are 1 a sequence of stream terraces 2 folded plio pleistocene fanglomerates and 3 an example of stream capture following a right lateral deflection or offset of several hundred metres a left step of the mission creek fault in pushawalla canyon is a probably cause of folds and sporadic uplift that produced the stream terraces possible cause of recent stream capture are 1 juxtaposition of pushawalla canyon with a relict canyon moving northwestward along the mission creek fault or 2 right lateral deflection or offset of pushawalla canyon along the fault with simultaneous headward erosion of a shorter steep stream flowing toward the coachella valley estimation of a slip rate and identification of paleoseismicity for the san andreas fault in the indio hills is difficult however degree of topographic dissection formation and preservation of desert pavement and relative soil profile development suggest that the age of the offset fan may be as old as 70 000 yr but that most likely it is on the order of 20 000 to 30 000 yr these age estimates for the offset fan indicate a minimum slip rate for the san andreas fault of 10 to 35 mm yr with about 23 to 35 mm yr the most likely the pattern of observed offset drainages is complex but suggests that during the past few thousand years creep events or moderately large earthquakes have periodically produced several metres of right lateral displacement

geomorphic and sedimentary response of rivers to tectonic deformation a brief review and critique of a tool for recognizing subtle epeirogenic deformation in modern and ancient settings abstract rivers are extremely sensitive to subtle changes in their grade caused by tectonic tilting as such recognition of tectonic tilting effects on rivers and their resultant sediments can be a useful tool for identifying the often cryptic warping associated with incipient and smaller scale epeirogenic deformation in both modern and ancient settings tectonic warping may result in either longitudinal parallel to floodplain orientation or lateral normal to floodplain orientation tilting of alluvial river profiles alluvial rivers may respond to deformation of longitudinal profile by 1 deflection around zones of uplift and into zones of subsidence 2 aggradation in backtilted and degradation in foretilted reaches 3 compensation of slope alteration by shifts in channel pattern 4 increase in frequency of overbank flooding for foretilted and decrease for backtilted reaches and 5 increased bedload grain size in foretilted reaches and decreased bedload grain size in backtilted reaches lateral tilting causes down tilt avulsion of streams where tilt rates are high and steady down tilt migration combing where tilt rates are lower each of the above effects may have profound impacts on lithofacies geometry and distribution that may potentially be preserved in the rock record fluvial sedimentary evidence for past tilting is traditionally based on the assumption that depositional features reminiscent of modern fluvial tectonic effects are evidence for past tectonic effects where it is closely associated with historically active structures or where non tectonic causes cannot be invoked however caution must be exercised when using these effects as criteria for past or current tectonic warping as these effects may be caused by non tectonic factors these non tectonic causes must be eliminated before tectonic interpretations are made

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

present day vertical deformation of the cascadia margin pacific northwest united states we estimate present day uplift rates along the cascadia subduction zone in california oregon and washington in the pacific northwest united states by utilizing repeated leveling surveys and tide gauge records these two independent data sets give similar profiles for latitudinal variation of contemporary uplift rates along the coast uplift rates are extended inland through east west leveling lines that connect the north south line along the coast to the north south line along the inland valleys just west of the cascades the results are summarized as a contour map of present day uplift rates for the western pacific northwest we find that rates of present day uplift vary latitudinally along the coast and inland valleys as well as longitudinally along transects connecting the coast to the inland valleys long term tidal records of neah bay astoria and crescent city indicate uplift of land relative to sea level of 1 6 0 2 0 0 0 2 and 0 9 0 2 mm yr respectively 1 standard error unlike previous estimates of relative sea level change at astoria we adjust for discharge effects of the columbia river including human management influences after approximating an absolute framework by using 1 8 0 1 mm yr to compensate for global sea level rise results indicate that much of the western pacific northwest is rising at rates between 0 and 5 mm yr the most rapid uplift rates are near the coast particularly near the olympic peninsula the mouth of the columbia river cape blanco and cape mendocino two axes of uplift are identified one trends northeast from the southwest oregon coast and the other trends south southeasterly from the olympic peninsula to the columbia river the puget sound vicinity and a small east west region from the north central oregon coast to the inland willamette valley are subsiding at rates up to 1 mm yr we interpret the overall pattern of rapid present day uplift to be generated by interseismic strain accumulation in the subduction zone this interseismic elastic strain accumulation implies significant seismic hazard

use of liquefaction induced features for paleoseismic analysis an overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of holocene paleo earthquakes abstract liquefaction features can be used in many field settings to estimate the recurrence interval and magnitude of strong earthquakes through much of the holocene these features include dikes craters vented sand sills and laterally spreading landslides the relatively high seismic shaking level required for their formation makes them particularly valuable as records of strong paleo earthquakes this state of the art summary for using liquefaction induced features for paleoseismic interpretation and analysis takes into account both geological and geotechnical engineering perspectives the driving mechanism for formation of the features is primarily the increased pore water pressure associated with liquefaction of sand rich sediment the role of this mechanism is often supplemented greatly by the direct action of seismic shaking at the ground surface which strains and breaks the clay rich cap that lies immediately above the sediment that liquefied discussed in the text are the processes involved in formation of the features as well as their morphology and characteristics in field settings whether liquefaction occurs is controlled mainly by sediment grain size sediment packing depth to the water table and strength and duration of seismic shaking formation of recognizable features in the field generally requires a low permeability cap above the sediment that liquefied field manifestations are controlled largely by the severity of liquefaction and the thickness and properties of the low permeability cap criteria are presented for determining whether observed sediment deformation in the field originated by seismically induced liquefaction these criteria have been developed mainly by observing historic effects of liquefaction in varied field settings the most important criterion is that a seismic liquefaction origin requires widespread regional development of features around a core area where the effects are most severe in addition the features must have a morphology that is consistent with a very sudden application of a large hydraulic force this article discusses case studies in widely separated and different geological settings coastal south carolina the new madrid seismic zone the wabash valley seismic zone and coastal washington state these studies encompass most of the range of settings and the types of liquefaction induced features likely to be encountered anywhere the case studies describe the observed features and the logic for assigning a seismic liquefaction origin to them also discussed are some types of sediment deformations that can be misinterpreted as having a seismic origin two independent methods for estimating prehistoric magnitude are discussed briefly one method is based on determination of the maximum distance from the epicenter over which liquefaction induced effects have formed the other method is based on use of geotechnical engineering techniques at sites of marginal liquefaction in order to bracket the peak accelerations as a function of epicentral distance these accelerations can then be compared with predictions from seismological models

late holocene earthquakes on the toe jam hill fault seattle fault zone bainbridge island washington five trenches across a holocene fault scarp yield the first radiocarbon measured earthquake recurrence intervals for a crustal fault in western washington the scarp the first to be revealed by laser imagery marks the toe jam hill fault a north dipping backthrust to the seattle fault folded and faulted strata liquefaction features and forest soil a horizons buried by hanging wall collapse colluvium record three or possibly four earthquakes between 2500 and 1000 yr ago the most recent earthquake is probably the 1050 1020 cal calibrated yr b p a d 900 930 earthquake that raised marine terraces and triggered a tsunami in puget sound vertical deformation estimated from stratigraphic and surface offsets at trench sites suggests late holocene earthquake magnitudes near m7 corresponding to surface ruptures 36 km long deformation features recording poorly understood latest pleistocene earthquakes suggest that they were smaller than late holocene earthquakes postglacial earthquake recurrence intervals based on 97 radiocarbon ages most on detrital charcoal range from 12 000 yr to as little as a century or less corresponding fault slip rates are 0 2 mm yr for the past 16 000 yr and 2 mm yr for the past 2500 yr because the toe jam hill fault is a backthrust to the seattle fault it may not have ruptured during every earthquake on the seattle fault but the earthquake history of the toe jam hill fault is at least a partial proxy for the history of the rest of the seattle fault zone

axial river evolution in response to half graben faulting carson river nevada u s a abstract the holocene history of faulting and river channel movement for the carson valley nevada allows the tectonic alluvial interactions of an active half graben to be studied topographic surveys maps cores radiocarbon dates and paleohydrology are used to study the temporal and spatial patterns of carson river channel change the influence of faulting and associated ground tilting on channel movement is determined by comparing the pattern and timing of river movements with the published event history of the basin bounding fault inverse modeling of the fault history assuming rigid block motion suggests that surface gradients perpendicular to the channel and basin axis have progressively increased through the holocene from an initially horizontal surface the greater part of this movement occurred during and immediately after faulting channel avulsion in response to this increased tectonic ground tilting appears to be the most important factor controlling alluvial architecture although intrinsic fluvial processes and regional climate change may have triggered individual avulsions channel belts avulsed towards the fault onlap after each tectonic event during periods of tectonic quiescence they migrated away from the fault offlap taking the path of maximum overall gradient lag times between faulting and channel avulsion are very short instantaneous to hundreds of years the observed holocene history of the carson river is consistent with positions of channel belts predicted by half graben stratigraphic models and therefore this study provides the first confirmation that the underlying alluvial tectonic assumptions of these models are broadly correct

longshore sediment transport rate measurement and estimation central west coast of india abstract measurements of the longshore sediment transport rate lstr along the surf zone at a 4 km long beach on the central west coast of india were made over a 4 month period during the study both the lateral and vertical distributions of the sediment transport rate were measured with traps deployed on a line spanning the surf zone sediment transport in the swash zone was not considered in the present study the longshore current was measured at each trap location the breaking wave parameters were calculated from a directional wave buoy at 16 m water depth the measured values were compared with those calculated from three selected empirical formulas the standard coefficient values in the empirical formulas were used without calibration to the data sets the measured average gross transport was 726 m3 day and that calculated were 1108 1017 and 781 m3 day based on cerc walton and bruno and van rijn formula during the data collection 69 of the time the transport was direct towards north and in the remaining period it was direct towards south the correlation coefficient between the longshore sediment transport rates measured and those calculated by cerc walton and bruno and van rijn formula were 0 38 0 71 and 0 74 respectively the average rms error between the measured and the calculated longshore sediment transport rate based on cerc walton and bruno and van rijn formula were 0 91 0 57 and 0 47

glacio isostatic response of the puget sound area washington proglacial lake shorelines in the puget sound area were distorted by the isostatic response associated with recession of the cordilleran ice sheet about 18 000 13 500 yr ago the shorelines which are highest near the east west midpoint of the elongate lowland are upwarped northward with a regression slope of 0 85 0 04 m km 1 departures from the trend may have been caused by holocene tectonic warping calibrating this lacustrine record with data from the everson marine limit permits the actual rather than relative uplift to be estimated and contoured the high degree of isostatic equilibrium attained at least 50 during the brief loading hemicycle suggests that the mantle beneath this part of the cascadia subduction zone has anomalously low viscosity and strength crustal strain associated with the loading unloading cycle in the south central lowland appears to he correlated with the pattern of quaternary faulting and seismicity

two post glacial earthquakes on the saddle mountain west fault southeastern olympic peninsula washington abstract two earthquakes ruptured the western strand of the saddle mountain fault after the cordilleran ice sheet began its retreat from the puget sound lowland about 17 ka the fault system includes multiple northeast trending thrust faults on the southeastern olympic peninsula delineated on light detection and ranging topography by prominent east side up scarps that deform vashon till and extend over 6 7 km the cargill creek trench on the saddle mountain west fault exposed faulted drift and postglacial colluvium below a 1 2 m high scarp steeply dipping northeast striking faults form a 10 m wide zone beneath the scarp structural relations in the trench indicate that two earthquakes produced at least 1 m of vertical separation additional folding or faulting beyond the trench raised the scarp to a total height of 1 7 m aligned cobbles dipping approximately 40 to the north attest to earthquake related tilting a cobble firmly lodged in till and split by a secondary fault indicates that hanging wall deformation involved a dextral component of slip however slip on the master fault may have involved a left lateral component based on slip indicators at adjacent trench sites in the region a single charcoal age and estimates of the onset of ice retreat limit the time of the oldest earthquake to 17 7 7 ka the most recent event occurred after 1 7 ka and may be the same earthquake that dammed price lake about 1100 yr ago known from related studies empirical relations suggest that the most recent earthquake was about m 7 0 2 and produced an estimated total slip of 1 3 1 7 m the total postglacial slip rate ranges from 0 1 to 0 3 m k yr these results support the hypothesis that the saddle mountain fault is part of a larger fault system that accommodates transpressive strain as the puget lowland crust migrates around the eastern flank of the olympic mountains

sediment transport on the mid continental shelf in onslow bay north carolina during hurricane isabel abstract hurricane isabel made landfall on the southeastern u s coast along the lower outer banks of north carolina near cape lookout nc on september 18 2003 an instrumented quadrapod frame moored approximately 43 5 km off the coast of wilmington nc in onslow bay at a depth of approximately 30 m was present on the shelf when the hurricane passed approximately 160 km from onslow bay the attached instrumentation includes a downward looking pulse coherent acoustic doppler profiler pc adp and an upward looking acoustic doppler current profiler adcp simultaneous measurements of flow velocities from the surface to the seabed along with acoustic backscatter measurements and seabed elevation were obtained during this storm event three days prior to the direct effects of the hurricane long period swells 14 17 s began to impact the area causing sediment transport to occur on the mid shelf shear velocities calculated from a bottom boundary layer model ranged from approximately 6 to 10 cm s 1 over the course of the sediment transport event based on shear velocity calculations bedload and suspended sediment transport were occurring at the site 72 h prior to the passage of the hurricane as long period swells reached heights of 4 m the seabed altimeter recorded large fluctuations during the storm but was unable to trace elevation changes due to the presence of a highly concentrated layer of suspended sediments in the lower 10 cm of the bottom boundary layer large amounts of suspended sediment transport occurred in the along shelf direction towards the southwest after tropical storm force winds of 30 m s 1 began to directly affect the area and wind driven currents were generated wind driven subtidal currents responded rapidly to local wind forcing and shifted from 15 cm s 1 towards the southwest to 16 cm s 1 towards the northeast model calculated velocity profiles compared well with measured current velocity profiles boxcores collected pre and post storm show a storm layer of approximately 5 cm and a sediment trap that was attached to the frame 30 cm above the bed collected approximately 400 cm3 of fine to medium sands that were suspended during the storm