conceptual framework for assessing the response of delta channel networks to holocene sea level rise abstract recent research has identified two fundamental unit processes that build delta distributary channels the first is mouth bar deposition at the shoreline and subsequent channel bifurcation which is driven by progradation of the shoreline the second is avulsion to a new channel a result of aggradation of the delta topset the former creates relatively small branching networks such as wax lake delta the latter generates relatively few long distributaries such as the mississippi and atchafalaya channels on the mississippi delta the relative rate of progradation to aggradation and hence the creation of accommodation space emerges as a controlling parameter on channel network form field and experimental research has identified sea level as the dominant control on holocene delta growth worldwide and has empirically linked channel network changes to changes in the rate of sea level rise here i outline a simple modeling framework for distributary network evolution and use this to explore large scale changes in holocene channel pattern that have been observed in deltas such as the rhine meuse and mississippi rapid early to mid holocene sea level rise forced many deltas into an aggradational mode where i hypothesize that avulsion and the generation of large scale branches should dominate slowing of sea level rise in the last 6000 yr allowed partitioning of sediment into progradation facilitating the growth of smaller scale distributary trees at the shorelines of some deltas and a reduction in the number of large scale branches significant antecedent topography modulates delta response the filling of large incised valleys for example caused many deltas to bypass the aggradational phase human effects on deltas can be cast in terms of geologic controls affecting accommodation constriction of channels forces rapid local progradation and mouth bar bifurcation while accelerated sea level rise increases aggradation and induces more frequent channel avulsion

mississippi river subaqueous delta is entering a stage of retrogradation abstract the subaqueous delta of the mississippi river the largest river system in the conterminous u s has entered a stage of retrogradation caused by multiple natural and anthropogenic activities since the 1950s the suspended sediment load of the mississippi river has decreased by 50 due primarily to the construction of 50 000 dams in the mississippi basin the impact of this decreased sediment load has been observed in subaerial environments but the impact on sedimentation and geomorphology of the subaqueous delta front has yet to be examined to identify historic trends in sedimentation patterns we compiled bathymetric datasets including historical charts industry and academic surveys and national oceanic and atmospheric administration hydrographic data collected between 1764 and 2009 the progradation rate measured at the 10 m depth contour of southwest pass which receives 69 of the suspended sediment load reaching head of passes has decreased from 67 m yr between 1874 and 1940 to 26 m yr between 1940 and 1979 with evidence of further deceleration from 1979 to 2009 at south pass and pass a loutre the delta front has entered the destructive phase with the 10 m contour retreating at rates 20 m yr at both passes since 1979 advancement of the delta front also decelerated in deeper water in some areas out to 180 m depth except locally where mudflow lobes are advancing deeper contours show a pattern of decreasing progradation rate between 1874 1940 and 1979 2005 time periods furthermore based on differences measured between available bathymetric datasets the sediment accumulation rate across the delta front decreased by 73 for the same period the retention rate of mississippi river sediment on the delta front ranged from 67 to 81 for the time periods assessed with total sediment load stored on the delta front equal to 317 54 mt yr from 1874 to 1940 145 25 mt yr from 1940 to 1979 and 87 15 mt yr from 1979 to 2005 we document for the first time that the mississippi river delta front has entered a phase of retrogradation which will likely be accelerated by future upstream activities that divert a portion of the sediment load to the upper delta for coastal protection and restoration projects the decline of the subaqueous mississippi river delta has critical implications for biogeochemical cycling subaqueous mass wasting and sediment dispersal to the coastal ocean

time space modeling of the dynamics of santorini volcano greece during the 2011 2012 unrest the 2011 2012 unrest of santorini thera volcano aegean sea greece was associated with microseismicity confined to the kameni line kl a major tectonovolcanic lineament and has been regarded as a single magmatic episode produced by a spherical source derived from inversion of gps data however such a source is a few kilometers away from the kl and cannot explain observed microseismicity for this reason we divided the unrest episode into five periods based on the fluctuations of seismicity and deformation rates and investigated the connection between seismicity and two spherical magmatic point sources for each period based on a new inversion algorithm and consistent gps data we recognized during the volcano unrest episode an unstable pattern of intrusions correlating with both the kl and columbo line cl a second major tectonovolcanic lineament intrusions correlating with cl appear relatively persistent aseismic small and shallow which is consistent with marine geophysical evidence for arrested shallow dykes and geodetic evidence from a previous inflation episode during the two periods of intense seismicity sources close to the kl explaining seismicity were obtained this unstable pattern of intrusions explains both the well observed location and timing of seismicity as well as ground deformation and is consistent with results of an okada type inversion for a sill and a dyke the stress interactions between the two sources agree with coulomb failure stress models santorini appears to be affected by concurrent offset magma pulses and only recent activity from a magma pulse below the kl produced microseismic swarms

volcanology greek inflation circa 1600 bc a petrology study of the bronze age minoan eruption on the greek island of santorini finds that the sub volcanic magma reservoir was recharged in spurts during the decades to months that preceded the eruption see letter p 77 timothy druitt and co authors have studied pre eruptive magmatic processes and their timescales using chemically zoned crystals from the late 1600s bc minoan caldera forming eruption on the island of santorini greece despite the large volume of erupted magma and the 18 000 year gestation period between the minoan and the previous major eruption recharge of the magma reservoir seems to have occurred during the century before eruption and mixing between different magma batches was still taking place during the final months these observations have implications for monitoring strategies at long dormant but potentially active caldera systems such as long valley in california yellowstone in wyoming and campi flegrei in italy

shredding of environmental signals by sediment transport 1 landscapes respond to climate tectonic motions and sea level but this response is mediated by sediment transport understanding transmission of environmental signals is crucial for predicting landscape response to climate change and interpreting paleo climate and tectonics from stratigraphy here we propose that sediment transport can act as a nonlinear filter that completely destroys shreds environmental signals this results from ubiquitous thresholds in sediment transport systems e g landsliding bed load transport and river avulsion this morphodynamic turbulence is analogous to turbulence in fluid flows where energy injected at one frequency is smeared across a range of scales we show with a numerical model that external signals are shredded when their time and amplitude scales fall within the ranges of morphodynamic turbulence as signal frequency increases signal preservation becomes the exception rather than the rule suggesting a critical re examination of purported sedimentary signals of external forcing citation jerolmack d j and c paola 2010 shredding of environmental signals by sediment transport geophys res lett 37 l19401 doi 10 1029 2010gl044638

episodic overbank deposition as a dominant mechanism of floodplain and delta plain aggradation the common view that frequent overbank flooding leads to gradual aggradation of alluvial strata on floodplains and delta plains has been challenged by a variety of studies that suggest that overbank aggradation occurs in a strongly episodic fashion however this remains a largely untested hypothesis due to the difficulty in establishing age models with sufficiently high resolution here we use 39 optically stimulated luminescence osl ages from proximal overbank deposits in the mississippi delta to demonstrate for the first time that alluvial aggradation over centennial to millennial time scales is predominantly episodic with aggradation rates of 1 4 cm yr that can persist for centuries osl ages from three separate study areas produce age clusters that are distinctly different yet complement each other these findings suggest that a substantial portion of the continental stratigraphic record consists of patchworks of relatively discrete centennial to millennial scale sediment bodies assembled by autogenic processes

deciphering holocene sea level history on the u s gulf coast a high resolution record from the mississippi delta published holocene relative sea level rsl curves for the u s gulf coast are in mutual conflict with some characterized by a smooth rsl rise akin to widely accepted eustatic sea level curves versus others including several recent ones that are characterized by a conspicuous stair step pattern with prolonged millennium scale rsl stillstands alternating with rapid meter scale rises in addition recent work in texas and alabama has revitalized the notion of a middle holocene rsl highstand estimated at 2 m above present mean sea level an extensive sampling program in the mississippi delta louisiana focused on the collection of basal peats that accumulated during the initial transgression of the pre existing consolidated pleistocene basement we used stable carbon isotope ratios to demonstrate that many of these samples accumulated in environments affected by frequent saltwater intrusion in the 30 cm zone between mean spring high water and mean sea level and we selected plant macrofossils that were subjected to ams 14c dating nearly 30 sea level index points from a 20 km2 study area on the eastern margin of the delta suggest that rsl rise followed a relatively smooth trend for the time interval 8000 3000 cal yr b p thus questioning the occurrence of major rsl stillstands alternating with abrupt rises given the narrow error envelope defined by our data set any sea level fluctuations if present would have amplitudes of 1 m although a true middle holocene highstand never occurred in the mississippi delta the high level of detail of our time series enables a rigorous test of this hypothesis correction of our data set for a hypothetical tectonic subsidence rate of 1 1 mm yr 1 assuming a constant subsidence rate compared to the tectonically relatively stable adjacent coast of texas leads to sea levels near 2 m above present during the time interval 6000 4000 cal yr b p however this model also implies a rsl position near 2 m around 8000 cal yr b p which is inconsistent both with data of this age from texas as well as with widely accepted sea level data from elsewhere we therefore conclude that a middle holocene highstand for the u s gulf coast is highly unlikely and that the entire area is still responding glacio isostatically by means of forebulge collapse to the melting of the laurentide ice sheet

deltaic morphodynamics and stratigraphic evolution of middle barataria bay and middle breton sound regions louisiana usa implications for river sediment diversions abstract river sediment diversions have been recognized as a key strategy for offsetting land loss in coastal louisiana recently much attention has been focused on sediment capture from the main stem river and conveyance of that material through diversion outflows yet the performance and long term feasibility of diversions as land building agents also hinges upon the subsurface stratigraphic architecture of receiving basins a concept that has largely been unexplored a major core collection and analysis program was undertaken to study the geological properties of substrates in the middle barataria bay and middle breton sound diversion receiving basins louisiana usa over a region of 200 square kilometers in both basins 50 vibracores up to 5 5 m in length were collected in spring and summer of 2015 cores were logged for bulk density and imaged with a geotek multi sensor core logger split cores were then subsampled for granulometry organic content and 14c dating both receiving basins are characterized by 1 2 m of organic rich surficial strata underlain by 2 m of mineral rich sand and silt beds that display a greater bulk density additionally some cores contain deeper peaty strata intercalated within muds and sands 14c dates of these buried peats range between 1910 and 3203 calendar years before present demonstrating that relatively old deltaic strata exist at shallow depths age comparisons of stratigraphically similar peat beds from this study and previous delta lobe chronological models indicate that the st bernard lobe prograded eastward at a time averaged rate of 75 m yr from a geotechnical standpoint the surficial uncompacted

controls on natural levee development in the columbia river british columbia canada natural levees of the columbia river near golden british columbia were investigated to identify the mechanisms that control levee development and morphology topographic profiles of 12 levee pairs were surveyed and measurements of water surface elevation flow velocity flow direction and turbidity were obtained during an average magnitude flood 1ae2 years recurrence interval sedimentation rates and grain size distributions were measured from sediment traps placed along levee to floodbasin transects results show that water and sediment exchange between the channel and floodbasin was mainly by advection during flooding local floodbasins behave more as efficient water pathways than water storage features resulting in down valley floodbasin flows capable of limiting basinward growth of levees levee shape results primarily from two independent factors 1 maximum channel water stage which limits levee height and 2 floodbasin hydraulics which control width in the columbia river the competence of floodbasin flows results in relatively narrow and steep levees natural levees grow under two general conditions of deposition as governed by flood stage elevation relative to levee crest elevation front loading and back loading during large floods when crests are inundated front loading preferentially aggrades the proximal portions of levees with sediment directly from the channel thus increasing levee slope during average or below average floods when many levee crests are not overtopped back loading preferentially aggrades the distal levee areas and floodbasin floor reducing levee slope in the study area a balance between front and back loading sustains these narrow and steep levee shapes for long periods reflecting an equilibrium between hydraulic regime floodplain morphology and deposition

small scale stratigraphy in a large ramp delta recent and holocene sedimentation in the volga delta caspian sea the volga delta differs from all other major deltas in the world by its extremely gentle onshore and offshore gradient f5 cm km and by being affected by the rapid sea level changes of the caspian sea at rates up to a hundred times the global sealevel rise this paper reports 1 the morphological and facies development of part of the lower delta during the last full sealevel cycle between 1929 and 1995 as monitored using remote sensing and field mapping and 2 the holocene development of the delta from outcrop data and augered transects during a sea level fall of 3 m between 1929 and 1977 rapid progradation of levees composed of fine sand took place along over 800 distributary channels along the delta front smaller distributaries became filled with clay and organics during the 3 m sea level rise from 1977 to 1995 aggradation occurred leading to deposition of silt and clay on the levees and minor filling of the flood basins sedimentation rates as established with 137 cs dating are up to 2 5 cm year total thickness of holocene deposits in the lower delta plain is 4 10 m

deltas radiocarbon dating and measurements of sediment storage and subsidence in holocene marine deltaic sequences there is no simple relationship between radiocarbon age and depth of sampling the nile and ganges brahmaputra deltas show remarkably similar radiocarbon age depth relationships 1 most radiocarbon dates by conventional and accelerator mass spectrometric ams analyses are older some by 4000 yr than reasonably expected 2 dates are commonly inverted i e older upcore and 3 sample dates at delta surfaces commonly exceed 2000 yr b p these anomalous age depth phenomena are in part a response to reservoir effects introduction of old carbon and emphasized herein influence of sediment storage and remobilization that prevail in fluvial and delta plains in fluvial systems sediment generally is not transported in a single episode from its original source area to the sea rather material transported from upland reaches and river valley to coast is subject to a repeated series of depositional burial and erosional events induced by episodic flooding overbank sedimentation and channel migration because sediment is likely to be temporarily stored in the delta plain it is difficult to determine the time of a sediment9s final deposition and burial at a delta site a successful strategy requires use of several independent dating methods including ams analyses of in situ basal peats and fossils and where possible archaeological evaluation of associated artifacts that are in place accurate dates are needed for reliable measurement of rates of delta plain aggradation and land subsidence information to help implement effective coastal protection measures

barrier island arcs along abandoned mississippi river deltas abstract generation of transgressive barrier island arcs along the mississippi river delta plain and preservation of barrier shoreline facies in their retreat paths on the inner shelf is controlled by 1 shoreface translation 2 age of the transgression and 3 the thickness of the barrier island arc sediment package barrier island arcs experience an average relative sea level rise of 0 50 1 00 cm yr 1 and shoreface retreat rates range from 5 15 m yr 1 young barrier island arc sediment packages isles dernieres are thin and have experienced limited landward retreat of the shoreface older barrier island arcs chandeleur islands are thicker and have experienced significant landward movement of the shoreface because of the greater time available for retreat if the transgressed barrier shoreline sediment package lies above the advancing ravinement surface the entire sequence is truncated a thin reworked sand sheet marks the shoreface retreat path the base of the transgressive sediment package can lie below the ravinement surface in older barrier shorelines in this setting the superstructure of the barrier shoreline is truncated leaving the basal portion of the transgressive sequence preserved on the inner shelf a variety of transgressive stratigraphic sequences from sand sheets to truncated barrier islands to sand filled tidal inlet scars have been identified by high resolution seismic profiling across the shoreface retreat paths of mississippi delta barrier island arcs one of these examples the isles dernieres represents a recently detached barrier island arc in the early stages of transgression an older example the chandeleur islands represents a barrier island arc experiencing long term shoreface retreat this paper describes the stratigraphic character and preserved transgressive facies for the isles dernieres and chandeleur islands

upstream and downstream controls of recent avulsions on the taquari megafan pantanal south western brazil avulsion the natural relocation of a river is a key process in the evolution of subaerial fans river floodplains and deltas the causes of avulsion are poorly understood which is partly due to the scarcity of field studies of present avulsions at present two avulsions are occurring on the middle and lower taquari megafan pantanal basin south western brazil here we present an analysis of the causes of these avulsions based on field and remote sensing data and show that avulsions on megafans can be controlled by both upstream and downstream processes the middle fan avulsion started in 1997 1998 is a result of upstream control overbank aggradation was caused by the variable input of sandy sediment into the system which caused channel belt superelevation and also created an easily erodible subsurface favouring bank retreat crevassing and scour of deep floodplain channels the sandy subsurface in this area is inferred to have been a major factor in the causation of this avulsion under conditions of little gradient advantage the lower fan avulsion started c 1990 results from interplay of upstream and downstream controls the latter being related to the local base level the paraguay river floodplain at the toe of the fan channel and overbank aggradation on the lower fan was influenced by fan sub lobe progradation and channel backfilling fan sub lobe progradation caused a significant gradient advantage of the avulsion channel over the parent channel avulsions are commonly supposed to be preferentially triggered by high magnitude floods when there is considerable channel belt superelevation however both avulsions studied by us were triggered by small to average floods with modest channel belt superelevation we conclude that flood magnitude and channel belt superelevation have been overrated as causes of avulsion and demonstrate additional causes that influence the growth of crevasses into avulsions

pathways and processes associated with the transport of groundwater in deltaic systems summary rivers are considered to be the primary means driving hydrological and geochemical fluxes between the continents and the ocean however it is unclear how well surface water fluxes represent total fluxes or whether more diffuse subterranean fluxes of river water to the coastal ocean occur this question is important in light of research demonstrating that submarine groundwater discharge sgd is important for geochemical and hydrological fluxes here we examine the pathways and potential magnitude of the role that sgd plays in the mississippi river delta mrd the largest delta in north america we present multiple independent lines of evidence demonstrating a hydrological connection between the mississippi river mr and the mrd evidence includes hydrological budgets demonstrating downstream water losses from the mr which are unexplained and are of the same magnitude as water sources to adjacent coastal bays of the mrd well data indicating a correlation between groundwater height and the stage of the mr and excess 222 rn inventories exceeding that expected from in situ production implying an advective i e groundwater source to coastal bays sgd likely flows from the mr to its delta via paleochannels and other buried sand bodies seismic data indicates that such features are common whereas resistivity data suggest the intrusion of low salinity water to coastal bays adjacent to the river these results may be applicable to other deltas worldwide as many of the world largest rivers have deltas with numerous abandoned distributaries that could act as conduits for groundwater

development of the kura delta azerbaijan a record of holocene caspian sea level changes late holocene deposits of the kura delta indicate an alternating dominance of deltaic and shallow marine environments these major environment shifts are controlled by the high frequency sea level changes of the caspian sea the level of the caspian sea now at 27 m below global sea level gsl changes at rates of up to a hundred times as fast as global sea level allowing observation of sedimentary processes on a decadal scale that would take millennia in an oceanic environment the modern kura delta is a river dominated delta with some wave action along its north eastern flank and without tidal influence morphological and hydrological changes have been monitored for over 150 years continuing up to the present day using remote sensing imagery offshore sparker survey data onshore and offshore corings biostratigraphical analysis and radiometric dating enable a reconstruction of the holocene kura delta four phases of delta progradation alternating with erosional transgressive surfaces have been identified representing just as many cycles of sea level fall and rise the first cycle is represented by lowstand deposits truncated by a transgressive surface ts1 at ca 80 m below gsl ts1 is overlain by several metres of laminated clays and silts deposited during a late holocene forced regression h1 these deposits are truncated by the prominent reflector ts2 corresponding to the derbent lowstand around 1500 yr bp and subsequent transgression this transgressive surface is overlain by prograding shallowing upwards deposits h2 in turn truncated by a third transgressive surface ts3 correlated with a lowstand of ca 32 m below gsl the last phase h3 comprises an onshore progradational unit followed by an aggradational unit with an offshore veneer of clays and silts corresponding to the formation of the modern kura delta that started at the beginning of the 19th century

a revised chronology for mississippi river subdeltas radiocarbon measurements by accelerator mass spectrometry relating to three of the four late holocene mississippi river subdeltas yielded consistent results and were found to differ by up to 2000 carbon 14 years from previously inferred ages these geological dataare in agreement with archaeological carbon 14 data and stratigraphic ages based on ceramic seriation and were used to develop a revised chronologic framework which has implications for prehistoric human settlement patterns coastal evolution and wetland loss and sequence stratigraphic interpretations

drowning of the mississippi delta due to insufficient sediment supply and global sea level rise global sea level rise reduced sediment supply and subsidence threaten the stability of the mississippi delta calculations of riverine sediment load and storage indicate that 10 000 13 500 km2 of the delta could be submerged by ad 2100

influence of water and sediment supply on the stratigraphic record of alluvial fans and deltas process controls on stratigraphic completeness 1 stratigraphy contains the most complete record of information necessary to quantitatively reconstruct paleolandscape dynamics but this record contains significant gaps over a range of time and space scales these gaps result from stasis on geomorphic surfaces and erosional events that remove previously deposited sediment building on earlier statistical studies we examine stratigraphic completeness in three laboratory experiments where the topography of aggrading deltas was monitored at high temporal and spatial scales the three experiments cover unique combinations in the absolute magnitudes of sediment and water discharge in addition to generation of accommodation space through base level rise this analysis centers on three time scales 1 the time at which a record is discretized t 2 the time necessary to build a deposit with mean thickness equivalent to the maximum roughness on a surface tc and 3 the time necessary for channelized flow to migrate over all locations in a basin tch these time scales incorporate information pertaining to the time variant topography of actively changing surfaces kinematics by which the surfaces are changing and net deposition rate we find that stratigraphic completeness increases as a function of t tc but decreases as a function of tc tch over the parameter space covered in the experiments our results suggest that environmental signals disconnected from a sediment routing system are best preserved in systems with low tc values nondimensionalizing t by tc however shows that preservation of information characterizing system morphodynamics is best preserved in stratigraphy constructed by systems with low water to sediment flux ratios

new evidence on the spatial temporal distribution of superlobes in the yellow river delta complex abstract unraveling the spatial temporal distribution of delta superlobes precisely is particularly important and challenging in the yellow river delta complex yrdc previous research on this issue can be dated back to the early 1990s when the paleoenvironmental reconstructions mainly hinged on the historical documents and geomorphologic analysis of well developed cheniers from the west coast of bohai bay and only few drilled cores with scant radiocarbon dates were available to build a refined model of the holocene stratigraphic architecture and reconstruct the sedimentary evolution of the yrdc detailed sedimentological investigation of 12 boreholes including 59 new ams 14c radiocarbon dates was combined with other published 25 cores and 174 ams 14c dates therein age depth curves were grouped by stratigraphic positions and facies characteristics of these 233 radiocarbon dated samples across different sectors of the yrdc exhibiting consistent patterns that can be used to identify distinct phases of delta superlobe activities eight new superlobes with relatively accurate dating spans were therefore proposed in the yrdc our results demonstrate that very high aggradation rates almost invariably correlate with the onset of deltaic deposition age depth patterns thus may be very useful to elucidate the complex sedimentary evolution of delta systems with multiple lobes

recent decadal growth of the atchafalaya river delta complex effects of variable riverine sediment input and vegetation succession abstract the mississippi river delta plain has experienced substantial wetland loss from subsidence erosion and sea level rise threatening coastal communities and the ecosystems that support them the atchafalaya river the largest distributary of the mississippi river has one of the few prograding delta features along the 200 km deltaic coastline understanding changes in the atchafalaya river delta complex ardc development has critical implications for future prediction and management strategy for the mississippi river delta plain this study was organized to answer two major questions 1 how did development of the ardc respond to fluctuation in riverine sediment supply over the period 1989 2010 and 2 has vegetation succession helped stabilize subaerial land the study quantified annual total suspended sediment yields to the two ardc subdeltas atchafalaya river subdelta arsd and wax lake outlet subdelta wlsd classified delta land cover using satellite imagery over 5 year intervals into three classes barren land vegetation and open water and investigated the relationship of delta land change with sediment yield and vegetation succession over the entire 21 year study period we found a net land gain of 59 km 2 with the arsd accounting for 58 of this gain and wlsd 42 sediment yield to the subdeltas decreased from an average annual of 38 megatonnes mt for arsd and 18 mt for wlsd during 1989 1995 to an average annual of 24 mt for arsd and 17 mt for wlsd during 2004 2010 corresponding to the decrease in riverine suspended sediment concentration concurrently total land growth rate decreased from 2 4 km 2 y 1 to 1 6 km 2 y 1 for arsd and 3 2 km 2 y 1 to 0 6 km 2 y 1 for wlsd however the ardc had a net land loss of 2 1 km 2 during 1999 2004 because of tropical system effects in conjunction with the lack of large river floods defined as discharge 13 800 m 3 s 1 on average more than 60 of newly vegetated land remained vegetated in subsequent years and when compared with barren areas vegetated land was less likely 7 3 vs 32 to be converted to water indicating vegetative stabilization effect however during the period without a major flood vegetation buffering against tropical system erosion was limited this indicates that over the period 1989 to 2010 land growth of the ardc was dictated by large flood events

interlinked barrier chain and delta lobe development northern gulf of mexico abstract a wealth of new data provides a well constrained chronology of mid to late holocene coastal development in the louisiana mississippi borderland that may also be utilized in a globally applicable sedimentation model barrier sand and deltaic mud sequences illustrate a process by which potential ground water and hydrocarbon reservoir rocks accumulated unusually rapidly and were preserved set against decelerating holocene sea level rise and locally variable subsidence rates the study provides an example of the interplay between an emerging prograding and partially stranded barrier island chain a sizable estuary and several extensive delta lobes utilizing microfossil fauna based depositional facies information and archaeological data absolute dates helped to reconstruct the history of the alabama louisiana barrier chain and deltas between ca 5 7 and ca 1 5 14c ka bp protected by the substantial dune cover that prevented island submersion the regional eustastic transgression paradoxically was synchronous with significant progradational barrier and deltaic regression the earliest barrier islands emerged ca 4 6 4 4 14c ka bp ca 5 7 5 0 cal years when sea level stood at ca 1 0 to 1 5 m these islands isolated mississippi sound from the greater gulf of mexico the absence of a lagoonal inshore sediment interval beneath the islands and the 3 15 m thick basal nearshore marine muddy sandy unit that blankets the pleistocene surface refutes the transgressive history of barrier initiation the islands aggraded on a 3 0 16 5 m thick fine sandy shallow marine regressive platform lithosome that in turn overlies a transgressive muddy sandy nearshore marine lower sediment interval avulsion of the mississippi river had abruptly reduced nearshore salinities by ca 3 9 3 7 ka 14c bp renewed mississippi delta growth induced rapid aggradation and progradation on the opposite pearl river delta mainland shore as well gulf influences have rapidly diminished in areas so affected a new absolute chronology of the mississippi st bernard delta lobes constrains these events delta growth and mainland progradation first isolated then severely constricted the lake borgne embayment accompanied by ongoing subsidence the western barriers were stranded then buried shoaling related to st bernard delta progradation interfered with westward littoral drift to maintain cat island archaeology provided important supplementary data for dating environmental changes refuting earlier suggestions that native colonization rapidly followed delta complex formation the earliest known indian sites postdated the start of the associated st bernard delta lobe by 1 9 3 1 14c ka

geomorphology and quaternary stratigraphy the roles of morpho litho and allostratigraphy abstract the subdivision and ordering of quaternary sediments and landforms is very often based on geomorphology quaternary landforms such as moraines river terraces palaeoshorelines and indeed any other landform can be arranged and ordered in time based on their relative position in the landscape morphostratigraphy is the subdivision of sedimentary units primarily on the basis of surface form whilst surface form is often used as a criterion for separating sedimentary units morphostratigraphy also usually incorporates lithological criteria to aid stratigraphical subdivision and morpho and lithostratigraphy are often interlinked in quaternary science however another approach allostratigraphy has increasingly been applied to subdivide and order quaternary sediment landforms allostratigraphy uses discontinuities to subdivide sedimentary successions allostratigraphy enables lateral variations in lithology to be included within the same stratigraphical unit furthermore it enables lithologically similar sediments stacked on top of each other to be divided into separate units based on discontinuities this paper examines the applications of morpho litho and allostratigraphy to subdivide sediment landform assemblages and critically reviews their role in quaternary stratigraphy

mass wasting on the mississippi river subaqueous delta abstract the mississippi river delta front mrdf is an excellent natural laboratory for studying seafloor instability and evaluating the preconditioning factors and triggering mechanisms that lead to seafloor failures the occurrence of seafloor landslides on the mrdf has been recognized since the 1950s but the bulk of research on the topic was conducted in the 1970s 80s after seafloor landslides triggered by hurricane camille damaged offshore infrastructure through these efforts it was recognized that seafloor instability features are present across the entire delta front that rapid sediment delivery from the mississippi river is a primary preconditioning factor for failures and that cyclic loading from hurricane waves is the main triggering mechanism for deep seated catastrophic events however mounting evidence shows that mrdf seafloor motion occurs even during periods of no hurricane activity which could be attributed to creep like motion of underconsolidated sediment or smaller episodic flows triggered by winter storms or mississippi river floods given the extensive spatial distribution of instabilities on the mrdf the multiple mechanisms of failure and variety of resulting morphology and the range of potential triggering mechanisms with short recurrence the mrdf is an exceptional location to assess the complex problem of seafloor landslides an improved understanding of seafloor landslides is crucial for understanding global sediment budgets and associated biogeochemical cycling as they can evacuate large volumes of sediment into deep water over short time periods additionally seafloor landslides pose a hazard to offshore infrastructure and to coastal communities through possible tsunami inundation and advancing research on preconditioning factors and triggering mechanisms would improve hazard assessments this paper presents a review and synthesis of geological and geotechnical research on the mrdf particularly with respect to seafloor landslides their occurrence geological and geotechnical controls triggering mechanisms and knowledge gaps related thereto this synthesis is conducted at times of rapidly developing technologies for studying seafloor instability and as the mrdf enters a stage of degradation characterized by reduced sediment delivery and accumulation

stratigraphic relations of santorini s intracaldera fill and implications for the rate of post caldera volcanism we propose a new volcanological interpretation of santorini s intracaldera fill deposits as revealed by seismic reflection profiles this interpretation along with supplementary gravity and geophysical studies reveals three distinct volcaniclastic units 1 3 from top to bottom these units are attributed to 1 modern infilling sediment 2 shallow marine phreatomagmatic volcanism associated with the relatively recent formation of the kameni islands and 3 downfaulted minoan pyroclastic deposits which formed during caldera collapse towards the end of the bronze age eruption estimates of the volumes of the seismic units and kameni islands yield a dense rock equivalent magma volume of 4 85 0 7 km 3 the average rate of volcanism over the past c 3641 years is estimated at 1 3 10 3 km 3 a 1 and is similar to the rate since the ad 1707 eruption of 1 2 10 3 km 3 a 1 based on historical lava volume estimates

integrating geochronologic and instrumental approaches across the bengal basin constraining time is of critical importance to evaluating the rates and relative contributions of processes driving landscape change in sedimentary basins the geomorphic character of the field setting guides the application of geochronologic or instrumental tools to this problem because the viability of methods can be highly influenced by geomorphic attributes for example sediment yield and the linked potential for organic preservation may govern the usefulness of radiocarbon dating similarly the rate of sediment transport from source to sink may determine the maturity and or light exposure of mineral grains arriving in the delta and thus the feasibility of luminescence dating here we explore the viability and quirks of dating and instrumental methods that have been applied in the bengal basin and review the records that they have yielded this immense dynamic and spatially variable system hosts the world s most inhabited delta outlining a framework for successful chronologic applications is thus of value to managing water and sediment resources for humans here and in other populated deltas worldwide our review covers radiocarbon dating luminescence dating archaeological records and historical maps short lived radioisotopes horizon markers and rod surface elevation tables geodetic observations and surface instrumentation combined these tools can be used to reconstruct the history of the bengal basin from late pleistocene to present day the growing variety and scope of bengal basin geochronology and instrumentation opens doors for research integrating basin processes across spatial and temporal scales

three dimensional model of alluvial stratigraphy theory and applications abstract a three dimensional model of alluvial stratigraphy has been developed to simulate the spatial distribution proportion and connectedness of coarse grained channel belt deposits in alluvial strata as a function of channel belt width floodplain width bankfull channel depth channel belt and overbank sedimentation rates avulsion location and period compaction and tectonism tilting and faulting in this model a floodplain surface of variable width and length is occupied by a single channel belt changes in floodplain topography are produced by spatial and temporal variation of channel belt and floodplain deposition rates and by compaction and local or regional tectonism the location and timing of avulsions are determined by local changes in floodplain slope relative to channel b lt slope and by flood magnitude and frequency the diverted channel belt follows the locus of maximum floodplain slope at the end of each simulation architectural parameters are calculated including channel deposit proportion and connectedness and the dimensions of channel belt sandstone bodies three dimensional perspective diagrams mesh surfaces and two dimensional stratigraphic sections can be plotted to illustrate depositional surfaces time planes and the location and geometry of coarse grained channel belt deposits within finer grained overbank deposits the model predicts that channel belt proportion and connectedness and dimensions of sandstone bodies vary as a function of distance from avulsion points and cross section orientation upstream from avulsion points sandstone bodies have low width thickness ratios because of aggradation in a fixed channel belt immediately downstream from avulsion points channel belts tend to be connected resulting in sandstone bodies with high width thickness ratios avulsion sequences develop where points of avulsion shift up valley with a progressive decrease in avulsion period such sequences may produce successions in which channel belt proportion and connectedness vary vertically with a cyclic period of 103 to 105 years down valley increases in aggradation rate or down valley decreases in floodplain slope for example associated with a rise in base level may result in an increase in channel belt proportion and connectedness because of high avulsion frequencies in down valley regions of the floodplain down valley decreases in aggradation rate as in alluvial fans foreland basins and during base level fall may result in high avulsion frequencies in up valley parts of the floodplain tectonic tilting and faulting locally increase avulsion probabilities and channel belts generally shift toward areas of maximum subsidence under certain conditions however depositional topography may cause channels to shift away from areas of maximum subsidence channel deposit proportion and connectedness are gen rally high near downthrown areas of the floodplain but distribution clustering of channel belts may not be a reliable indicator of fault geometry or displacement models of alluvial architecture that consider only sediment accumulation rate as the main controlling factor are oversimplified the three dimensional model presented here predicts many of the features of channel behavior observed in modern rivers but there is a pressing need for better models and adequate natural data to test them

middle and late holocene avulsion history of the river rhine rhine meuse delta netherlands at present little evidence is available on avulsion rates avulsion frequencies and interavulsion periods of aggrading fluvial systems over time scales of millenia the large number of high quality 14c ages from the holocene rhine meuse delta central netherlands enables a detailed assessment of such avulsion parameters and an evaluation of the factors controlling avulsion frequency 14c histogram analysis indicates that instantaneous avulsion coexistence of successive channel belts for less than a few centuries has dominated in this area interavulsion periods were typically 1000 yr although values of 500 or 5000 yr have also been found avulsion frequency was especially large prior to 4300 cal yr b p indicating a strong control by aggradation rate in turn controlled by sea level rise in addition periods with high avulsion frequency appear to correlate with time intervals characterized by large scale transgressive tendencies the time interval with the largest number of coexisting distributaries corresponds to the period with dominance of anastomosing fluvial style

an equilibrium profile model for retreating marsh shorelines in southeast louisiana abstract louisiana s coastal marshes are experiencing the highest wetland loss rates in the u s in part due to subsidence driven relative sea level rise these marshes are also vulnerable to the erosive power of wave attack 1 on the marsh edge adjacent to open water bodies and 2 after the marsh platform is submerged marsh shorelines in barataria bay breton sound and the active balize delta of southeastern louisiana were examined in areas where the subaerial marsh platform had disappeared since 1932 vibracore transects of marsh and adjacent bay surface sediments to 2 m depth were analyzed using geotechnical stratigraphic and radiochemical 137 cs and 210 pb methods and the subaerial to subaqueous transition of the marsh was mapped for elevation using standard stadia rod transit and fathometer measurements results indicate that marsh edge erosion of the platform takes place subaqueously until water depths of 1 5 m are reached this is observed even in interior pond regions but the shoreface elevation profiles are a function of fetch exposed open bay sites display greater incision depth and rate of the marsh platform than protected interior bay or pond sites core stratigraphy reveals that the outer part of the subaqueous platform switches from erosional to depositional as retreat proceeds covering the incised marsh deposits unconformably with estuarine shelly muds 137 cs and excess 210 pb activity indicates that these muds are deposited within a few decades of subaerial marsh loss the consistency of the cross shore profile results suggests that a single profile of equilibrium can approximate the morphology of eroding marsh edges in southeast louisiana platform stratigraphy and resistance to erosion have a limited effect on profile shape this equilibrium profile and remote sensing images of shoreline change are used to estimate the sediment yield to adjacent estuarine areas by this process on average 1 5 m3 of sediment are yielded per m shoreline length annually from both barataria bay and breton sound due to the highly organic nature of the eroded sediment 30 this supply of organic rich material could significantly impact estuarine productivity and hypoxia on the louisiana continental shelf

a new algorithm for modelling simple and double mogi magma sources in active volcanoes accuracy sensitivity limitations and implications a new algorithm for modelling one or two mogi magma sources in actively deforming volcanoes is proposed using santorini thera greece volcano as a test site this algorithm is based on a quasi deterministic grid scan search followed by a topological inversion in rn space it avoids point solutions and local minima and is primarily designed for gps observations it can be extended to other types of magma sources defined by closed functions and to other types of data a validation of the method used an accuracy oriented approach a comparison between true or reference and inverse modelled magma sources which revealed bias free precise magma source solutions a validation of the algorithm for false alarms i e for identification of non existent sources produced by computation artefacts was also made computed solutions correspond to point sources affecting idealized media homogeneous elastic half spaces and hence ignore errors induced by magma source and lithology complexities which should be superimposed to obtain the total error budget still the solutions allow modelling of the propagation of measurement errors because of the mathematical model adopted this problem has previously been ignored a sensitivity analysis of results obtained using this method permit us to predict and quantify expected bias and uncertainties in modelled magma sources as a function of their depth and of the observation networks increased bias and noise in solutions for specific observations networks and types of data are inferred and this may explain reported discrepancies in various magma source models some implications for the santorini volcano which had an unrest episode in 2011 2012 are that the algorithm can lead to less noisy solutions of the mogi sources that the surface deformation may be recognized as resulting from inflation of two spherical sources and that differences in magma source models using different types of data may only indicate predictable uncertainties in the solutions

a geoarchaeological perspective on the challenges and trajectories of mississippi delta communities recent geochronology of the mississippi delta of coastal louisiana usa provides a high resolution record of land growth that facilitates the study of ancient settlement patterns in relation to delta evolution we use stratigraphy and optically stimulated luminescence osl dating to show that two late holocene earthen mounds were constructed several hundred years after the land emerged from open water this multi century pause allowed natural processes of overbank and crevasse splay deposition to elevate the land surface reduce flood risk and foster desirable environmental conditions prior to human occupation these results are applied to obtain new age constraints for a large number of at risk or lost archaeological sites with little to no absolute chronology we use our findings to comment on prehistoric contemporary and future human landscape interactions in the mississippi delta and other deltaic environments

mississippi delta subsidence primarily caused by compaction of holocene strata coastal subsidence causes sea level rise shoreline erosion and wetland loss which poses a threat to coastal populations this is especially evident in the mississippi delta in the southern united states which was devastated by hurricane katrina in 2005 the loss of protective wetlands is considered a critical factor in the extensive flood damage the causes of subsidence in coastal louisiana attributed to factors as diverse as shallow compaction and deep crustal processes remain controversial current estimates of subsidence rates vary by several orders of magnitude here we use a series of radiocarbon dated sediment cores from the mississippi delta to analyse late holocene deposits and assess compaction rates we find that millennial scale compaction rates primarily associated with peat can reach 5mm per year values that exceed recent model predictions locally and on timescales of decades to centuries rates are likely to be 10 mm or more per year we conclude that compaction of holocene strata contributes significantly to the exceptionally high rates of relative sea level rise and coastal wetland loss in the mississippi delta and is likely to cause subsidence in other organic rich and often densely populated coastal plains

relation of sequence stratigraphy to modern sedimentary environments one method of testing the concept of sequence stratigraphy is to compare it to quaternary sediments in which chronology stratigraphic relations and facies geometry are more clearly understood than in older rocks rapid deposition rates during quaternary glacial eustatic cycles in large deltaic depocenters generate sequences comparable to those in the ancient stratigraphic record in the northern gulf of mexico the late wisconsinan holocene mississippi river has deposited a type 1 sequence that includes lowstand transgressive and high stand systems tracts characteristics of modern mississippi river sedimentary environments support the methodology used in sequence analysis but the short time taken for sequence generation here raises important questions about sequence time scales correlation and driving mechanisms

simulation of birdfoot delta formation with application to the mississippi delta 1 recently seybold et al 2007 proposed a reduced complexity model which simulates the process of delta formation on geological time scales it includes subaerial and subaqueous growth in a three dimensional framework in this paper we apply this model to the formation of a river dominated delta and compare the model dynamics with observations of the formation of the balize lobe of the mississippi river delta the model generates both subaerial and subaqueous channels and lateral levee formations as well as a profile morphology with steep drop offs and a flat delta surface which is similar to natural ones we show that the dimensionless parameters of the model may be consistently rescaled to match the balize lobe this means that after rescaling the water flows the subaerial geometry and time the deposited subaqueous lobe volume the sediment and water flows the age as well as the sediment capture ratio match the observed data finally we use detrended fluctuation analysis to show that the modeled long term dynamics of the delta formation process shows a complex temporal correlation structure a characteristic time scale separates periods of consistent delta growth by gradual sediment deposition at the mouths of distributary channels from periods during which random large scale channel avulsions lead to rapid change and the formation of new channels and subaqueous dominated deposition

degradation of the plaquemines sub delta and relative sea level in eastern mississippi deltaic coast during late holocene abstract the stratigraphic architecture of plaquemines sub delta lobe is identified from sedimentary cores and sub bottom seismic data collected at lower breton sound louisiana usa four lithofacies were identified in cores from bottom to top 1 organic poor mud 2 organic poor silty sand 3 massive mud 4 organic rich peat and root rich soft mud overall the lithofacies displays a typical progradational deltaic deposit at bottom with upward coarsening feature and then an upward fining deposit overlying on top stratigraphic position of the organic rich peat facies indicates that it is formed after the fluvial sediment source moves away from this region and it is recognized as a termination of progradation of the plaquemines sub delta dated peat samples show that sub delta progradation stops between 876 and 1384 yr ad during which a 20 70 cm relative sea level rise is detected the geological framework reported in this study provides critical information for future modeling on river diversions the stratigraphic architecture underlying lower breton sound implicates that top three facies of root rich soft mud organic rich peat and massive mud are likely to be eroded away before the development of new crevasse splay or sub delta when sediment diversion is in operation the deeper organic poor silty sand lithofacies however can serve as a firm foundation to build new land

sea level rise and coastal marsh sustainability geological and ecological factors in the mississippi delta plain chronostratigraphic approaches to coastal geomorphology frequently include consideration of salt marsh deposits as indicators of past sea level positions continuous horizons of such deposits can be used to infer that salt marshes were keeping pace with local rates of relative sea level rise rslr rates of past accumulation estimated using dating techniques are then used to hindcast the rate of sea level rise in that area estimates of contemporary sea level rise rates are often derived from tide gauge records this approach allows identification of subdecadal variations in mean water level accumulation rates of both organic and inorganic sediments can also be derived at these time scales and studies from many coastal marshes demonstrate the episodic nature of inorganic sediment deposition the frequency and spacing of these events does not necessarily coincide with periods of increased local sea level in addition short term increases in sea level could result in marsh deterioration as soils become excessively waterlogged a conceptual model of changes in geomorphic and ecological processes contributing to marsh sustainability during the holocene has been developed for the mississippi delta plain mdp the survival of some marshes in this area despite high rates of subsidence indicates that the combined effect of organic and inorganic accumulation processes can be adequate to sustain coastal marshes in the face of sea level rise

chronology and controls of avulsion along a mixed bedrock alluvial river tooth stephen rodnight h duller g a t mccarthy t s 2006 chronology and controls of avulsion along a mixed bedrock alluvial river geological society of america bulletin 119 3 pp 452 461 rae2008

dating modern deltas progress problems and prognostics 1 abstract radiocarbon dating is the method most frequently used to date holocene deltaic sequences but less than one quarter of 14c dates are within 500 years of predicted age such dates tend to be unreliable in other words often too old and commonly inverted upsection and core sample dates obtained near deltaic plain surfaces may be as old as mid to late holocene stratigraphic irregularities result primarily from downslope reworking of upland alluvial sediment with displacement of old carbon in the sediment that accumulates in lower valleys and deltaic plains use of dates that are too old results in inaccurately calculated rates most often too low of relative sea level rise and or land subsidence more reliable timing of deltaic sediment requires a multiple method dating approach including where possible identification of associated archaeological material developing an accurate dating strategy is a critical step for implementing reliable coastal protection measures needed for the rapi

controls on river delta formation insights from numerical modelling abstract primary hydraulic and sedimentary controls on river deltas were previously postulated in classification schemes in the field of sedimentary geology based on many field observations however detailed mechanistic models were restricted to the river dominated delta class analogous to the concept of morphological conditioning here we show that antecedent stratigraphy controls morphometrics of prograding river dominated delta distributary networks under steady sea level further we use coupled hydrodynamic morphodynamic stratigraphic detailed numerical modelling to assess the influence of wind generated waves and tides on clastic river delta formation our synthetic simulations show that deltas forming under mere riverine forcing prograde via sequences of mouth bar induced flow bifurcation and upstream channel shifting windwave action suppresses sequestration of fine sediments on the developing delta plain entailing relatively smooth shorelines perturbed by a limited number of distributary channels in contrast tide influenced river deltas are found to prograde mainly via lengthening of initially formed relatively stable distributaries as well as being characterized by cyclicity in deposits interbedding of sands and silts these results provide a framework for physics based river delta modelling under various environmental conditions particularly our findings suggest that relatively low energetic basin conditions can already significantly impact morphological and stratal patterns of prograding river deltas

holocene avulsion styles and sedimentation patterns of the saskatchewan river cumberland marshes canada abstract this paper describes the styles and sedimentation patterns of holocene avulsions of the saskatchewan river at the cumberland marshes predating the most recent 1870 s avulsion holocene avulsions involved two major styles 1 progradation of lacustrine deltas and splay complexes and 2 local reoccupation or appropriation of preavulsive channels most avulsions were progradational and occurred in floodplain lakes occupying floodbasin areas between elevated alluvial ridges the two most recent avulsions old channel and 1870 s diverted mainly into inundated peatland progradational avulsions were accompanied by deposition of avulsion belt sediments associated with multiple channel networks the characteristics of avulsion belt deposits include 1 sediments dominated by poorly sorted silt and very fine sand 2 lateral continuity in transverse and longitudinal directions with subhorizontal upper and lower boundaries 3 predominantly nonerosional contacts with underlying sediments 4 coarsening upward successions 5 consistent radiocarbon dates for the tops of preavulsive substrates and 6 occurrence beneath levee and overbank deposits of the associated major channel belt indicating that avulsion belt deposition occurs prior to the development of a new master channel the width of ancient avulsion belts reaches 18 km with typical thicknesses of 2 3 m avulsion belt deposition accompanied by many small channels was followed by flow reversion to a few larger channels and eventually to one single channel accompanied by deposition of levee and channel deposits reoccupational avulsions were not accompanied by deposition of widespread avulsion belt sediments and led mainly to the modification of pre existing channel belts the sedimentation patterns of holocene avulsions of the saskatchewan river reveal that avulsion belt sediments represent major components of the floodplain deposits supporting the model developed from observations of the 1870 s avulsion

enhancing mud supply from the lower missouri river to the mississippi river delta usa dam bypassing and coastal restoration abstract sand transport to the mississippi river delta mrd remains sufficient to build wetlands in shallow sheltered coastal bays fed by engineered diversions on the mississippi river mr and its atchafalaya river ar distributary but suspended mud silt clay flux to the coast has dropped from a mean of 390 mt y 1 in the early 1950s to 100 mt y 1 since 1970 this fine grained sediment travels deeper into receiving estuarine basins and plays a critical role in sustaining existing marshes virtually all of the 300 mt y 1 of missing mud once flowed from the missouri river mor basin before nearly 100 dams were built as part of the pick sloan water development project about 100 mt y 1 is now intercepted by main stem upper mor dams closed in 1953 but the remaining 200 mt y 1 is trapped by impoundments built on tributaries to the lower mor in the 1950s and 1960s sediment flux during the post dam high mor discharge years of 1973 1993 and 2011 approached pre dam levels when tributaries to the lower mor including the platte and kansas rivers contributed to flood flows west bank tributaries drain a vast arid part of the great plains while those entering from the east bank traverse the lowlands of the mor floodplain both provinces are dominated by highly erodible loess soils staunching the continued decline in mr fine grained sediment flux has assumed greater importance now that engineered diversions are being built to reconnect the lowermost mr to the mrd tributary dam bypassing in the lower mor basin could increase mud supply to the mrd by 100 200 mt y 1 within 1 2 decades such emergency measures to save the mrd are compatible with objectives of the missouri river restoration and platte river recovery programs to restore mor riparian habitat for endangered species rapid mobilization to shunt fine grained sediments past as many as 50 lower mor tributary dams in several u s states will undoubtedly require as much regional coordination and funding in the 21st century as the monumental effort it took to build the dams in the last century

backwater controls of avulsion location on deltas river delta complexes are built in part through repeated river channel avulsions which often occur about a persistent spatial node creating delta lobes that form a fan like morphology predicting the location of avulsions is poorly understood but it is essential for wetland restoration hazard mitigation reservoir characterization and delta morphodynamics following previous work we show that the upstream distance from the river mouth where avulsions occur is coincident with the backwater length i e the upstream extent of river flow that is affected by hydrodynamic processes in the receiving basin to explain this observation we formulate a fluvial morphodynamic model that is coupled to an offshore spreading river plume and subject it to a range of river discharges results show that avulsion is less likely in the downstream portion of the backwater zone because during high flow events the water surface is drawn down near the river mouth to match that of the offshore plume resulting in river bed scour and a reduced likelihood of overbank flow furthermore during low discharge events flow deceleration near the upstream extent of backwater causes enhanced deposition locally and a reduced channel fill timescale there both mechanisms favor preferential avulsion in the upstream part of the backwater zone these dynamics are fundamentally due to variable river discharges and a coupled offshore river plume with implications for predicting delta response to climate and sea level change and fluvio deltaic stratigraphy

rapid and widespread response of the lower mississippi river to eustatic forcing during the last glacial interglacial cycle the lower mississippi valley provides an exceptional fi eld example for studying the response of a continental scale alluvial system to upstream and downstream forcing associated with the large orbitally controlled glacialinter glacial cycles of the late quaternary however the lack of a numerical chronology for the widespread pleistocene strata assemblage known as the prairie complex which borders the holocene fl oodplain of the lower mississippi river has so far precluded such an analysis here we apply optically stimulated luminescence osl dating mainly on silt sized quartz from prairie complex strata in total 27 osl ages indicate that the prairie complex consists of multiple allostratigraphic units that formed mainly during marine isotope stages 7 5e and 5a thus the aggradation of the prairie complex is strongly correlated with the sea level highstands of the last two glacialinterglacial cycles fluvial incision during the sea level fall associated with the mis 5a mis 4 transition extended as far inland as 600 km from the present day shoreline testifying to the dominant downstream control of fl stratigraphic architecture in the lower mississippi valley in addition the short reaction time of the lower mississippi river suggests that large fl uvial systems can respond much more rapidly to allogenic forcing than is commonly believed

bang month scale eruption triggering at santorini volcano the time lag between intrusion of fresh hot magma and an ensuing eruption is of critical importance in both understanding the triggering and mitigating the consequences of volcanic eruptions this work looks at material erupted during 1925 28 at the nea kameni volcanic center in santorini greece to determine this time scale by exploiting fe mg diffusion in olivine crystals we constrained the intrusion to eruption time lag to between 3 and 10 weeks these techniques have potential application at many volcanic centers previously erupted material can be used to calibrate records of the short time scale processes common to many volcanic centers

a revised holocene geochronology for the lower mississippi valley data from two locations 1 a hydrodam site at the old river diversion structure south of the latitude of natchez ms and 2 eight water wells from the latitude of baton rouge la are the basis for a revised holocene geochronology of the lower mississippi river floodplain based on 84 radiocarbon dates analyses of 64 borehole logs and 75 grain size analyses which together provide major insight into questions concerning the complexity of meander belt movement the influence of the younger dryas on the lower valley and on the pleistocene holocene interface following the younger dryas the early holocene was characterized by periodic flooding and deposition separated by times of little or no deposition

rapid evolution of coastal lagoons in response to human interference under rapid sea level change a south caspian sea case study this research is part of the phd of the first author entitled evaluation of sefidrud delta south west caspian sea during the last millennium which was funded by brunel university london grant no r85104 the publication is a contribution to the inqua quicklakeh project no 1227 and to the european project marie curie climseas pirses ga 2009 247512

spatial variation of overbank aggradation rate and its influence on avulsion frequency river avulsions are commonly considered to be driven by the aggradation and growth of alluvial ridges and the associated increase in cross valley slope relative to either the down channel slope or the down valley slope the latter is termed the slope ratio in the present paper therefore spatial patterns of overbank aggradation rate over stratigraphically relevant time scales are critical in avulsion dominated models of alluvial architecture detailed evidence on centennial to millennial scale floodplain deposition has to date been largely unavailable new data on such long term overbank aggradation rates from the rhine meuse and mississippi deltas demonstrate that the rate of decrease of overbank deposition away from the channel belt is much larger than has been supposed hitherto and can be similar to observations for single overbank floods this leads to more rapid growth of alluvial ridges and more rapid increase in slope ratios potentially resulting in increased avulsion frequencies a revised input parameter for overbank aggradation rate was used in a three dimensional model of alluvial architecture to study its effect on avulsion frequency realistic patterns of avulsion and interavulsion periods 1000 years were simulated with input data from the holocene rhine river with avulsions occurring when the slope ratio is in the range 3 5 however caution should be practised with respect to uncritical use of these numbers in different settings evidence from the two study areas suggests that the avulsion threshold cannot be represented by one single value irrespective of whether critical slope ratios are used as in the present study or superelevation as has been proposed by other investigators

the mississippi delta region past present and future the mississippi delta region of south louisiana houses a wealth of resources within a dynamic subsiding landscape foundations for the delta region reflect neogene evolution of the depocenter whereas details of the modern landscape reflect late pleistocene to holocene evolution of the alluvial deltaic plain the holocene delta plain was constructed by cyclical growth of deltaic headlands followed by avulsion and relocation of the fluvial sediment source abandoned headlands were then submerged and reworked while a new headland was created at the site of active fluvial sediment input historic period levees have decoupled the delta plain from its fluvial sediment source at the same time global sea level rise was accelerating which has accelerated delta plain submergence diversions of mississippi river water and sediment are necessary to achieve delta plain sustainability but upstream dams trap 50 of the total sediment load and there is not enough supply to keep pace with subsidence and accelerated

interplay between tectonics and compaction in a rift margin lacustrine delta system miocene of the eger graben czech republic the early miocene bilina palaeodelta consists of fluvio deltaic and lacustrine clastics deposited along the south eastern margin of the extensional most basin part of the eger graben in north bohemia czech republic the bilina succession shows evidence of repeated advances of an axial deltaic system across a thick accumulation of organic material and clay in the hangingwall of an active fault exposures up to ca 4 5 km long in the bilina open cast mine help bridge the gap between seismic scale and typical outcrop scale of observation and thus allow the relationships between small scale and basin scale stratal geometries to be evaluated the bilina palaeodelta deposits include sand dominated fluvial channel fills and heterolithic sheets interpreted as delta plain strata sand dominated mouth bar wedges and heterolithic sheets of prodeltaic deposits passing distally into lacustrine clays the depositional environment is interpreted as a fluvial dominated mixed load lacustrine delta with a high degree of grain size segregation at the feeder channel mouths on the largest temporal and spatial scales variable tectonic subsidence controlled the overall advance and retreat of the delta system the medium term transgressive regressive history was probably driven by episodes of increased subsidence rate however at this temporal scale the architecture of the deltaic sequences deltaic lobes and correlative lacustrine deposits was strongly affected by i compaction of underlying peat and clay which drove lateral offset stacking of medium term sequences and ii growth of a fault propagation fold close to the active bilina fault at the smallest scale the geometries of individual mouth bars and groups of mouth bars short term sequences reflect the interaction among sediment loading compaction and growth faulting that produced high frequency relative lake level fluctuations and created local accommodation at the delta front

basin scale reconstruction of the geological context of human settlement an example from the lower mississippi valley usa abstract large river valleys integrate hydroclimatic change differently than smaller ones whereas sedimentary deposits in smaller valleys serve to record temporally short lived and or low amplitude hydrological and geomorphic responses larger valleys are relatively insensitive to changes at these scales however because of their size larger valleys archive sedimentary records of longer term geographically extensive flooding and climate related landscape evolution recent work in the upper tensas basin of the lower mississippi river valley usa demonstrates the utility of analyzing sediments from a large geomorphically and fluvially complex river basin as a proxy for significant climatic and landscape changes and their relation to human history a 6000 year sedimentary archive is used to explore the interplay between climate change landscape evolution and human responses to changing environmental parameters once the mississippi river basin stabilized following glacial retreat and deceleration of sea level rise the history of the river and its inhabitants was dominated by long periods of landscape stability punctuated by episodes of significant landform alteration modifications of the landscape are correlated with intervals of rapid climate change recorded in globally distributed multiproxy data sets periods of significant landscape instability and fluvial re adjustment are recorded for the periods ca 4800 3800 3000 2500 and 1000 800 cal bp these punctuations in the history of the lower mississippi valley are related to periods of major cultural transformation and suggest climate change plays a significant role in the long term history of human occupation in this river valley this research demonstrates how geoarcheology can provide information on human environmental relationships and long term landscape histories at temporal and spatial scales relevant to understanding cultural responses to climate change

geology geochronology and tectonic setting of late cenozoic volcanism along the southwestern gulf of mexico the eastern alkaline province revisited a nnw trending belt of alkaline mafic volcanic fields parallels the gulf of mexico from the u s border southward to veracruz state in eastern mexico previous studies grouped this volcanism into the so called beastern alkaline provinceq eap and suggested that it resulted from gulf parallel extensional faulting migrating from north to south from oligocene to present on the basis of new geologic studies forty nine unspiked k ar and two 40 ar 39 ar ages we propose a new geodynamic model for the volcanism along the southwestern gulf of mexico we studied in detail four of the six recognized fields of mafic alkaline volcanism in veracruz state 1 the lavas flows of tlanchinol area 7 3 5 7 ma 2 the alamo monogenetic field and sierra de tantima 7 6 6 6 ma 3 the poza rica and metlatoyuca lava flows 1 6 1 3 ma and 4 the chiconquiaco palma sola area 6 9 3 2 ma other two mafic volcanic fields may represent the continuation of alkaline volcanism to the southeast the middle miocene lavas at anegada high offshore port of veracruz and the middle to late miocene volcanism at the los tuxtlas the existence of major neogene extensional faults parallel to the gulf of mexico i e n s to nnw sse proposed in previous works was not confirmed by our geological studies elongation of volcanic necks vent alignment and faults mapped by subsurface data trend dominantly ne to ene and nw to nnw these directions are parallel to transform and normal faults that formed during the late jurassic opening of the gulf of mexico ascent of mafic magmas was likely facilitated and controlled by the existence of these pre existing basement structures

avulsion frequency avulsion duration and interavulsion period of holocene channel belts in the rhine meuse delta the netherlands abstract avulsion parameters greatly influence alluvial architecture because they determine channel density and interconnectedness reliable data on avulsion parameters is still scarce from a detailed reconstruction of the holocene avulsion history of the whole rhine meuse delta we determined quantitative values for the avulsion parameters avulsion frequency avulsion duration and interavulsion period in the rhine meuse delta the number of coeval channels is related to the avulsion frequency calibrated 14c intensity histograms are used to analyze 14c dates of beginning and ending river activity the histograms show that instantaneous and gradual avulsions were almost equally important in the rhine meuse delta a high avulsion frequency occurred from 8000 to 7300 cal yr bp a total of 17 avulsions i e 2 43 avulsions 100 years during this period the avulsion frequency was related to the high rate of sea level rise which induced fluvial sedimentation in the present near coastal area after 7300 cal yr bp avulsion frequency decreased as a result of a continuously decreasing rate of sea level rise from 7300 to 3200 cal yr bp avulsion frequency was low 35 avulsions took place within 4100 years 0 85 avulsions 100 years approximately 5000 cal yr bp the coastal barriers became closed and large scale peat formation occurred this resulted in fixation of the river channels and low cross valley gradients reducing the chances for avulsion between 3200 and 1400 cal yr bp avulsion frequency was high again a total of 34 avulsions i e 1 89 avulsions 100 years as a result of increased discharge and or within channel sedimentation which enhanced chances for avulsion the period of activity of channel belts shows no significant trend on the time scale of the holocene it is highly variable and averages 1280 820 cal yr the avulsion duration fluctuates between less than 200 and 1250 cal years and averages 335 cal years the avulsion duration shows no significant trend through time and remained constant until at least 1900 cal yr bp avulsion duration seems not to be influenced by aggradation rate average interavulsion period is shorter than the period of activity of channel belts and is approximately 945 cal years in the rhine meuse delta on the time scale of the holocene interavulsion period and avulsion duration are on average constant therefore the number of coeval channels is directly related to avulsion frequency available evidence from other rivers and deltas around the world however suggests that the relationship between these avulsion parameters is not everywhere the same

decadal to monthly timescales of magma transfer and reservoir growth at a caldera volcano caldera forming volcanic eruptions are low frequency highimpact events capable of discharging tens to thousands of cubic kilometres of magma explosively on timescales of hours to days with devastating effects on local and global scales1 because no such eruption has been monitored during its long build up phase the precursor phenomena are not well understood geophysical signals obtained during recent episodes of unrest at calderas such as yellowstone usa and campi flegrei italy are difficult to interpret and the conditions necessary for large eruptions are poorly constrained2 3 here we present a study of pre eruptive magmatic processes and their timescales using chemically zoned crystals from the minoan caldera formingeruption of santorini volcano greece4 which occurred in the late 1600s bc the results provide insights into how rapidly large silicic systems may pass from a quiescent state to one on the edge of eruption5 6 despite the large volume of erupted magma4 40 60 cubic kilometres and the 18 000 year gestation period between the minoan eruption and the previous major eruption most crystals in the minoan magma record processes that occurred less than about 100 years before the eruption recharge of the magma reservoir by large volumes of silicic magma and some mafic magma occurred during the century before eruption and mixing between different silicicmagmabatches was still taking place during the final months final assembly of large silicic magma reservoirs may occur on timescales that are geologically very short by comparison with the preceding repose period with major growth phases immediately before eruption these observations have implications for the monitoring of long dormant but potentially active caldera systems

avulsions channel evolution and floodplain sedimentation rates of the anastomosing upper columbia river british columbia canada ages of channels of the anastomosing upper columbia river south eastern british columbia canada were investigated in a cross valley transect by c 14 dating of subsurface floodplain organic material from beneath levees the avulsion history within the transect was deduced from these data and morphological stages in channel development were recognized additionally floodplain sedimentation rates were established the new data demonstrate that the upper columbia river is a long lived dynamic anastomosing system results show that anastomosis at the study location has persisted since at least 2700 cal years bp with avulsions occurring frequently at least nine channels have formed in the studied cross valley transect within the past 3000 years channel lifetimes from formation to abandonment appear to be highly variable ranging from approximately 800 to 3000 years log jams provoking avulsions and or silting up of old channels are proposed as reasons for this variability long term average floodplain sedimentation rates appear to be significantly lower than previously proposed by smith 1983 int assoc sedimentol spec publ 6 155 168 a long term 4550 years average of 1 75 mm per year after compaction was based on c 14 dates whilea short term sedimentation rate of 0 8 mm was determined for a single relatively small seasonal flood in 1994 using sediment traps however short term sedimentation rates vary considerably over the floodplain with levees aggrading up to four times faster than floodbasins channels of the upper columbia river anastomosed reach follow a consistent pattern in their development with each stage being characterized by different morphology and processes channel evolution comprises the following succession 1 avulsion stage in which a crevasse splay channel deepens by scour and levee sedimentation 2 widening and deepening stage in which bank slumping and bed scouring dominates 3 infilling stage in which either channel narrowing bank accretion or channel shallowing bed accretion takes place and 4 abandonment stage in which the residual remnant channel is filled exclusively by silt clay and organic material vertical stacking super imposition of active channels on recent channel fill sand bodies is a notable feature of the upper columbia river which suggests that reoccupation of residual channels is a common process

refining the link between the holocene development of the mississippi river delta and the geologic evolution of cat island ms implications for delta associated barrier islands abstract the geologic evolution of barrier islands is profoundly influenced by the nature of the deposits underlying them many researchers have speculated on the origin and evolution of cat island in mississippi but uncertainty remains about whether or not the island is underlain completely or in part by deposits associated with the past growth of the mississippi river delta in part this is due to a lack of comprehensive geological information offshore of the island that could augment previous stratigraphic interpretations based on terrestrial borings an extensive survey of cat island and its surrounding waters was conducted including shallow water geophysics e g high resolution chirp seismic side scan sonar and swath and single beam bathymetry and both terrestrial and marine vibracoring high resolution seismic data and vibracores from south and east of the island show two horizontally laminated silt units marine radiocarbon dates indicate that they are st bernard delta complex sbdc deposits furthermore seismic data reveal that the sbdc deposits taper off toward the southern shoreline of cat island and to the west morphology consistent with the distal edge of a delta complex the sedimentology and extent of each unit suggest that the lower unit may have been deposited during an earlier period of continuous river flow while the upper unit may represent reduced or sporadic river flow osl dates from the island platform beneath beach ridge complexes indicate three stages of terrestrial evolution island emergence resulting from relative sea level rise 5400 ybp island aggradation via littoral transport 2500 4000 ybp and island degradation due to delta mediated changes in wave direction present 3600 ybp finally the combination of terrestrial and marine data shows that portions of cat island that are lower in elevation than the central part of the island are younger and are likely underlain by a thin layer of deltaic sediments this underscores the potential for increased future vulnerability of barrier islands that develop adjacent to major river delta complexes