shoreline response to autogenic processes of sediment storage and release in the fluvial system 1 experimentally determined shoreline migration rates show high frequency autogenic variability superimposed on low frequency allogenic shoreline responses induced by eustatic base level change this variability persists even when the shoreline migration is averaged laterally indicating time variation in total sediment discharge reaching the shoreline the magnitude of autogenic variability in shoreline migration rate changes by roughly a factor of 3 depending on the shoreline migration direction it is strongest during transgression when the shoreline is on average migrating against the mean sediment flow and weakest during regression when the shoreline is migrating with the mean sediment flow we propose that this time variation is due to overall sediment storage and release in the fluvial system we use a one dimensional geometric model to model the autogenic signals observed in the experiment the model uses small periodic changes in the fluvial slope to represent the effects of storage and release of supplied sediment due to intrinsic variation in the transport efficiency of the fluvial system the periodic pulses of sediment discharge to the shoreline required in the model to explain the variations in shoreline migration can exceed by an order of magnitude the mean allogenic sediment discharge the slope variability required in the model to explain the autogenic shoreline signals is 1 4 of the mean slope this is well within the range of observed variability in depositional fluvial slopes we propose that at least part of this observed variability is real that is the long profile slope of a depositional river system may have an intrinsic elasticity of a few percent of its mean value even under steady forcing autogenic slope variation of this magnitude could readily produce parasequence scale deposits in the stratigraphic record

varying discharge controls on timescales of autogenic storage and release processes in fluvio deltaic environments tank experiments 1 changes in external forcing have traditionally been the main areas of interest in understanding sedimentary records while in most stratigraphic interpretation autogenic behavior has been thought of as a noise generator this study aims to investigate autogenic processes in a fluvio deltaic system under a range of discharge conditions and to show that autogenic processes generate distinct signatures rather than random noise a matrix of nine different experiments is presented here to systematically evaluate the effects of sediment and water discharge variations on the timescale of fluvial autogenic processes temporary sediment storage regularly occurs by backfilling of sediment in the fluvio deltaic channels followed by a period of strong channelization that releases the stored sediment these storage and release processes cycle along with changes in the fluvial slope and planform pattern of the flow here we propose that the autogenic behavior of deltaic progradation has a distinct timescale that is controlled by sediment and water discharges an increase in sediment discharge primarily reduces the autogenic timescale as higher sediment supply fills the channels faster in contrast the high sediment discharge causes a morphologic feedback by increasing the magnitude of fluvial slope change between the storage and release events and increasing the size of the temporary sediment storage termed the fluvial envelope this works against the sediment discharge control as the autogenic timescale is increased increasing the water discharge increases the autogenic timescale by improving the fluvial organization toward a strongly channelized system changes in autogenic timescale due to variations in the sediment and water discharges are nonlinear for different sediment to water discharge ratios as the ratio decreases the fluvial system is better organized and the timescale is more linearly related to the change in sediment discharge as the ratio increases deltas develop poorly organized fluvial systems and the associated timescales converge even with different sediment discharges the results presented here provide enhanced interpretation of sedimentary records by better decoupling of autogenic signatures from allogenic products developed across a wide range of discharge conditions

tsunami inundation modeling for western sumatra a long section of the sunda megathrust south of the great tsunamigenic earthquakes of 2004 and 2005 is well advanced in its seismic cycle and a plausible candidate for rupture in the next few decades our computations of tsunami propagation and inundation yield model flow depths and inundations consistent with sparse historical accounts for the last great earthquakes there in 1797 and 1833 numerical model results from plausible future ruptures produce flow depths of several meters and inundation up to several kilometers inland near the most populous coastal cities our models of historical and future tsunamis confirm a substantial exposure of coastal sumatran communities to tsunami surges potential losses could be as great as those that occurred in aceh in 2004

significant effect of sediment cohesion on delta morphology delta morphology is thought to be controlled by factors such as river discharge tides and waves numerical modelling shows that sediment cohesion also strongly influences the development of a delta s characteristics the morphologies of the world s deltas are thought to be determined by river discharge tidal range and wave action 1 more recently sea level rise 2 3 and human engineering4 have been shown to shape delta evolution the effects of factors such as sediment type and the overall amount of sediment carried by rivers are considered secondary4 5 6 in particular the role of sediment cohesion which is controlled by sediment size and type of vegetation is unclear here we use a numerical flow and transport model7 8 9 10 to show that sediment cohesiveness also strongly influences the morphology of deltas we find that holding all other factors constant highly cohesive sediments form bird s foot deltas with rugose shorelines and highly complex floodplains whereas less cohesive sediments result in fan like deltas with smooth shorelines and flat floodplains in our simulations sediment cohesiveness also controls the number of channels that form within the deltas and the average angle of bifurcation of those channels as vegetation generally acts as a cohesive agent we suggest that deltas that formed before the expansion of land plants in the devonian period should show fan like characteristics a finding consistent with the limited data from the sedimentological record11

stochastic analysis of tsunami runup due to heterogeneous coseismic slip and dispersion 1 most tsunami models apply dislocation models that assume uniform slip over the entire fault plane followed by standard analytical models based on volterra s theory of elastic dislocations for the seabed deformation in contrast we quantify tsunami runup variability for an earthquake with fixed magnitude but with heterogeneous rupture distribution assuming plane wave propagation i e an infinitely long rupture a simple stochastic analysis of 500 slip realizations illustrates the expected variability in coseismic slip along a fault plane and the subsequent runup that occurs along a coastline in the near field because of the need for systematically analyzing different fault geometries grid resolutions and hydrodynamic models several hundred thousand model runs are required thus simple but efficient linear models for the tsunami generation propagation and runup estimation are used the mean value and variability of the maximum runup is identified for a given coastal slope configuration and is analyzed for different dip angles on the basis of the ensemble runs nonhydrostatic effects are discussed with respect to their impact on generation nearshore propagation and runup we conclude that for the geometry and magnitude investigated nonhydrostatic effects reduce the variability of the runup that is hydrostatic models will produce an artificially high variability

26th december 2004 great sumatra andaman earthquake co seismic and post seismic motions in northern sumatra trench parallel thrust faults verging both landward and seaward were mapped in the portion of wedge located between northern sumatra and the indian indonesian boundary the spatial aftershocks distribution of the 26th december 2004 earthquake shows that the post seismic motion is partitioned along two thrust faults the lower and median thrust faults the latter being right laterally offset by a n s lower plate fracture zone located along the 93 6 n meridian between february 2005 and august 2005 the upper plate aftershock activity shifted from southeast of this fracture zone to northwest of it suggesting that the lower plate left lateral motion along the fracture zone may have induced a shift of the upper plate post seismic activity along the median thrust fault based on swath bathymetric and 3 5 khz data co seismic deformations were weak close to the trench joint seismic geodetic determination of slip distribution and time arrivals and heights of tsunami waves suggest that the co seismic slip was maximum along a portion of the upper thrust fault located north of the tuba ridge suggesting that the upper thrust fault might be a splay fault originated at the interplate fault plane as the upper thrust fault is steeper than the slab the vertical motion of the adjacent outer arc and overlying water is much larger compared to the one resulting from slip on the megathrust alone increasing tsunamogenic effects

parallel implementation of dispersive tsunami wave modeling with a nesting algorithm for the 2011 tohoku tsunami because of improvements in offshore tsunami observation technology dispersion phenomena during tsunami propagation have often been observed in recent tsunamis for example the 2004 indian ocean and 2011 tohoku tsunamis the dispersive propagation of tsunamis can be simulated by use of the boussinesq model but the model demands many computational resources however rapid progress has been made in parallel computing technology in this study we investigated a parallelized approach for dispersive tsunami wave modeling our new parallel software solves the nonlinear boussinesq dispersive equations in spherical coordinates a variable nested algorithm was used to increase spatial resolution in the target region the software can also be used to predict tsunami inundation on land we used the dispersive tsunami model to simulate the 2011 tohoku earthquake on the supercomputer k good agreement was apparent between the dispersive wave model results and the tsunami waveforms observed offshore the finest bathymetric grid interval was 2 9 arcsec approx 5 m along longitude and latitude lines use of this grid simulated tsunami soliton fission near the sendai coast incorporating the three dimensional shape of buildings and structures led to improved modeling of tsunami inundation

little ice age cold interval in west antarctica evidence from borehole temperature at the west antarctic ice sheet wais divide 1 the largest climate anomaly of the last 1000 years in the northern hemisphere was the little ice age lia from 1400 1850 c e but little is known about the signature of this event in the southern hemisphere especially in antarctica we present temperature data from a 300 m borehole at the west antarctic ice sheet wais divide results show that wais divide was colder than the last 1000 year average from 1300 to 1800 c e the temperature in the time period 1400 1800 c e was on average 0 52 0 28 c colder than the last 100 year average this amplitude is about half of that seen at greenland summit grip this result is consistent with the idea that the lia was a global event probably caused by a change in solar and volcanic forcing and was not simply a seesaw type redistribution of heat between the hemispheres as would be predicted by some ocean circulation hypotheses the difference in the magnitude of the lia between greenland and west antarctica suggests that the feedbacks amplifying the radiative forcing may not operate in the same way in both regions

autogenic response of fluvial deltas to steady sea level fall implications from flume tank experiments flume tank experiments on fluvial deltas conducted with constant fall of relative sea level rate a 0 constant sediment discharge q s and constant water discharge q w reveal a built in geomorphic process that inevitably causes valley incision autoincision after the beginning of the sea level fall and forms paired stream terraces on the abandoned alluvial slope despite steady sea level fall deltas aggrade without major incision until the autoincision threshold is attained at which time the aggradational regime is replaced by a degradational one results of the experiments imply that multiple valley incision and terrace formation can occur as an autogenic response of the depositional system to steady forcing by constant sea level fall changes of a q s and q w or changes in river energy are not required to account for these geomorphic events the understanding of the autogenic response when combined with the theory of shoreline autoretreat provides an alternative view of the geomorphic development of fluviodeltaic systems during base level fall

energy decay of the 2004 sumatra tsunami in the world ocean the catastrophic indian ocean tsunami generated off the coast of sumatra on 26 december 2004 was recorded by a large number of tide gauges throughout the world ocean this study uses gauge records from 173 sites to examine the characteristics and energy decay of the tsunami waves from this event in the indian atlantic and pacific oceans findings reveal that the decay e folding time of the tsunami wave energy within a given oceanic basin is not uniform as previously reported but depends on the absorption characteristics of the shelf adjacent to the coastal observation site and the time for the waves to reach the site from the source region in general the decay times for island and open ocean bottom stations are found to be shorter than for coastal mainland stations decay times for the 2004 sumatra tsunami ranged from about 13 h for islands in the indian ocean to 40 45 h for mainland stations in the north pacific

far field tsunami hazard from mega thrust earthquakes in the indian ocean summary we evaluate far field tsunami hazard in the indian ocean basin based on hydrodynamic simulations of ten case studies of possible mega earthquakes at the major seismic zones surrounding the basin they represent worst case scenarios of seismic rupture along the full extent of seismogenic faults having supported large earthquakes in the historical record in a series of numerical experiments in which the source parameters of the 2004 sumatra tsunami are allowed to vary one by one while keeping the seismic moment and the fault orientation unchanged we document that the main patterns of far field tsunami amplitudes are remarkably robust with respect to nominal variations in such parameters as hypocentral depth exact centroid location and slip distribution on the fault plane these results validate the concept of modelling case scenarios of potential future earthquakes whose source is by definition imprecise we consider seismic sources located at the extremities of the 2004 sumatra andaman rupture namely along the southern coast of sumatra and in the andaman myanmar province along the makran coast of pakistan and iran and also along the southern coast of java where the possibility of a large interplate thrust earthquake cannot be entirely dismissed the results of our hydrodynamic simulations indicate that the distribution of maximum amplitudes in the indian ocean basin is primarily controlled by the classical effect of source directivity and additionally by refraction and focusing along bathymetric features as a result many provinces in the basin could be threatened by higher tsunami amplitudes than in 2004 this pattern is particularly important along the coast of east africa from somalia to and including south africa in madagascar and the mascarene islands especially under a south sumatra scenario involving an earthquake comparable to or even possibly larger than the 1833 event whose epicentral area is widely believed to be under enhanced seismic risk as a result of stress transfer from the 2004 and 2005 ruptures to the northwest possibly even in the wake of the 2007 bengkulu earthquakes

deep sea observations and modeling of the 2004 sumatra tsunami in drake passage 1 the 2004 sumatra tsunami was clearly recorded by two uk bottom pressure gauges dpn and dps deployed in drake passage between south america and antarctica these open ocean records were examined to estimate characteristics of the tsunami waves and to compare the results of numerical simulations with the observations maximum wave heights measured at these gauges were 4 9 cm at dpn and 7 4 cm at dps the travel times from the source area were 19 h 46 min and 19 h 39 min respectively consistent with the times obtained from the nearby coastal tide gauges the numerical model described well the frequency content amplitudes and general structure of the observed waves with only small time shifts probably related to wave dispersion effects the shifts were 15 min for dpn and 10 min for dps with the modeled waves leading the observations in each case further inspection of the simulated and observed records revealed that the identified tsunami waves are related to the second main train of waves propagating by the energy conserving route along the mid ocean ridges while the first train of waves travelling by the fastest route across the ocean remained unrecognizable in the observed dps and dpn records and undetectable in the records of coastal tide gauges because of their insignificant amplitudes compared to the background variability

improved methods for pca based reconstructions case study using the steig et al 2009 antarctic temperature reconstruction abstracta detailed analysis is presented of a recently published antarctic temperature reconstruction that combines satellite and ground information using a regularized expectation maximization algorithm though the general reconstruction concept has merit it is susceptible to spurious results for both temperature trends and patterns the deficiencies include the following i improper calibration of satellite data ii improper determination of spatial structure during infilling and iii suboptimal determination of regularization parameters particularly with respect to satellite principal component retention this study proposes two methods to resolve these issues one utilizes temporal relationships between the satellite and ground data the other combines ground data with only the spatial component of the satellite data both improved methods yield similar results that disagree with the previous method in several aspects rather than finding warming concentrated in west antarctica the authors fi

cold conditions in antarctica during the little ice age implications for abrupt climate change mechanisms abstract the little ice age lia is one of the most prominent climate shifts in the past 5000 yrs it has been suggested that the lia might be the most recent of the dansgaard oeschger events which are better known as abrupt large scale climate oscillations during the last glacial period if the case then according to broecker 2000a 2000b antarctica should have warmed during the lia when the northern hemisphere was cold here we present new data from the ross sea antarctica that indicates surface temperatures were 2 c colder during the lia with colder sea surface temperatures in the southern ocean and or increased sea ice extent stronger katabatic winds and decreased snow accumulation whilst we find there was large spatial and temporal variability overall antarctica was cooler and stormier during the lia although temperatures have warmed since the termination of the lia atmospheric circulation strength has remained at the same elevated level we conclude that the lia was either caused by alternative forcings or that the sea saw mechanism operates differently during warm periods

impact of tidal currents on delta channel deepening stratigraphic architecture and sediment bypass beyond the shoreline deltas are sensitive indicators of coastal processes e g waves and tides and show dynamic changes in shoreline morphology distributary channel network and stratigraphic architecture in response to coastal forcing numerical modeling has long been used to show delta evolution associated with a single dominant coastal process but rarely to examine the sensitivity of deltas to mixed processes physics based morphodynamic simulations delft3d are used to investigate the influence of tidal currents on deltas tidal amplitude and the sand mud ratio of subsurface sediment have been varied in the model the results show that increasing tidal amplitude causes deeper and more stable distributary channels and more rugose planform shoreline patterns a new metric for channel geometry quantifies tidal influence on the distributary channel network stable distributary channels act as an efficient mechanism for ebb enhanced currents to 1 bypass sediment across the delta plain and 2 extend channel tips seaward through mouth bar erosion the basinward channel extension leads to sandier deposits in the tide influenced deltas than in their river dominated counterparts the delta front bathymetry also reflects sediment redistribution changing the delta front profile from concave to convex with compound geometries as tidal amplitude increases these results suggest that channel overdeepening is a possible tidal signature that should be considered when interpreting ancient systems and that sand may be bypassed much farther basinward in tide influenced than in purely river dominated deltas

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

braided stream aggradation on an alluvial fan margin emerald lake fan british columbia evolving bar and channel patterns were observed at the distal margin of an active alluvial fan at emerald lake british columbia during peak midsummer flows at the fan margin bed slope is 0 024 sediment is predominantly coarse gravel flow is shallow and fluctuating and sediment transport and deposition are dominated by chutes and lobes flow unconfinement at the exit of rapidly formed shallow scour channels typically results in deposition of sediment lobes 0 2 m thick and 10 250 m2 in area closely spaced deposition of a number of these sediment lobes results in aggradation of composite sediment sheets one such sheet monitored daily over a 15 day period deposited 129 m3 of gravel over 710 m2 of adjacent marsh sediment locally extending the distal fan margin by 39 m thickness of the aggraded bed varied up to 0 37 m depending on surface topography during active deposition individual lobe deposits formed simple unit bars that partly projected above the water surface these bars caused local flo

the great sumatra andaman earthquake of 26 december 2004 the two largest earthquakes of the past 40 years ruptured a 1600 kilometer long portion of the fault boundary between the indo australian and southeastern eurasian plates on 26 december 2004 seismic moment magnitude mw 9 1 to 9 3 and 28 march 2005 mw 8 6 the first event generated a tsunami that caused more than 283 000 deaths fault slip of up to 15 meters occurred near banda aceh sumatra but to the north along the nicobar and andaman islands rapid slip was much smaller tsunami and geodetic observations indicate that additional slow slip occurred in the north over a time scale of 50 minutes or longer

recent surface temperature trends in the interior of east antarctica from borehole firn temperature measurements and geophysical inverse methods 1 we use measured firn temperatures down to depths of 80 to 90 m at four locations in the interior of dronning maud land east antarctica to derive surface temperature histories spanning the past few decades using two different inverse methods we find that the mean surface temperatures near the ice divide the highest elevation ridge of east antarctic ice sheet have increased approximately 1 to 1 5 k within the past 50 years although the onset and rate of this warming vary by site histories at two locations nus07 5 78 65 s 35 64 e and nus07 7 82 07 s 54 89 e suggest that the majority of this warming took place in the past one or two decades slight cooling to no change was indicated at one location nus08 5 82 63 s 17 87 e off the divide near the recovery lakes region in the most recent decade inversion results indicate both cooler and warmer periods at different sites due to high interannual variability and relatively high resolution of the inverted surface temperature histories the overall results of our analysis fit a pattern of recent climate trends emerging from several sources of the antarctic temperature reconstructions there is a contrast in surface temperature trends possibly related to altitude in this part of east antarctica

contrasting morphodynamics in alluvial fans and fan deltas effect of the downstream boundary alluvial fans and fan deltas can in principle have exactly the same upstream conditions but fan deltas by definition have ponding water at their downstream boundary this ponding creates effects on the autogenic behaviour of fan deltas such as backwater adaptation mouth bars and backward sedimentation whereas alluvial fans may lack these effects hence the present authors hypothesize that morphodynamics on alluvial fans are determined primarily by upstream boundary conditions whereas morphodynamics on fan deltas are determined by both the upstream and the downstream boundary condition and changes therein to isolate the effects of the upstream and downstream boundaries five new alluvial fan experiments are compared with the details of three fan deltas published earlier that were formed under very similar and simple conditions similar to the fan deltas the alluvial fans build up by sheet flow whilst quasi regular periods of incision cause temporary channelized flow incision is followed by channel backfilling after which the fan returns to sheet flow the channelization and backfilling in alluvial fans is markedly less pronounced and more prone to autogenic disturbance than in fan deltas the difference is caused by morphodynamics at the downstream boundary in a fan delta the flow expansion of the channel causes deposition of all the sediment which forms a mouth bar and causes strong backfilling in an alluvial fan on the other hand the slope break at the fan perimeter causes some deposition but transport is not reduced to zero consequently the backfilling in alluvial fans is less pronounced than in fan deltas other published experiments support this trend removal of the mouth bar by a river leads to permanent channelization whilst pronounced mouth bar formation in highly channelized deltas promotes backward sedimentation the experimental results for this study predict that when alluvial fans prograde into lakes or deep rivers they transition to fan deltas with increasingly deeper channels and thicker backfill deposits

the tsunami of 26 december 2004 numerical modeling and energy considerations a numerical model for the global tsunamis computation constructed by kowalik et al 2005 is applied to the tsunami of 26 december 2004 in the world ocean from 80 s to 69 n with spatial resolution of one minute because the computational domain includes close to 200 million grid points a parallel version of the code was developed and run on a cray x1 supercomputer an energy flux function is used to investigate energy transfer from the tsunami source to the atlantic and pacific oceans although the first energy input into the pacific ocean was the primary direct wave reflections from the sri lankan and eastern shores of maldives were a larger source the tsunami traveled from indonesia around new zealand and into the pacific ocean by various routes the direct path through the deep ocean to north america carried miniscule energy while the stronger signal traveled a considerably longer distance via south pacific ridges as these bathymetric features amplified the energy flux vectors travel times for these amplified energy fluxes are much longer than the arrival of the first wave these large fluxes are organized in the wave like form when propagating between australia and antarctica the sources for the larger fluxes are multiple reflections from the seychelles maldives and a slower direct signal from the bay of bengal the energy flux into the atlantic ocean shows a different pattern since the energy is pumped into this domain through the directional properties of the source function the energy flow into the pacific ocean is approximately 75 of the total flow to the atlantic ocean in many locations along the pacific and atlantic coasts the first arriving signal or forerunner has lower amplitude than the main signal which often is much delayed understanding this temporal distribution is important for an application to tsunami warning and prediction

2004 indian ocean tsunami inflow and outflow at phuket thailand at bangtao beach phuket the 2004 indian ocean tsunami produced a repeated sequence in which rapid inflow of turbulent water was followed by ponding and then by gradual outflow photographs and eyewitness accounts show an initial withdrawal followed by series of inflows the tsunami left behind a sand sheet as much as 25 cm thick that contains parallel inclined landward and seaward lamina in addition to the normal grading commonly reported from tsunami deposits the sheet contains evidence for two times of vigorous inflow each of these is marked by mud rip ups medium to coarse sand that grades upward to fine landward inclined laminae and a sharp basal contact the top of the sand sheet when observed in the first days after the tsunami abounded in current dune and ripple bedforms of mostly landward orientation the tsunami s first positive wave left noonshore sedimentary record in this pitting area the second wave deposited sand that is much less extensive and slightly finer than that of the third wave the deposit of both these waves contains multiple fining upward sequences possibly due to multiple surges in one wave train the depth averaged flow velocity estimated from thickness and grain size are in the range 7 21 m s whereas a near bottom threshold velocity calculated from bedforms reveals the order of magnitude difference from 1 74 to 1 03 m s 2007 elsevier b v all rights reserved

the 2010 chilean tsunami off the west coast of canada and the northwest coast of the united states the major m w 8 8 chilean earthquake of 27 february 2010 generated a trans oceanic tsunami that was observed throughout the pacific ocean waves associated with this event had features similar to those of the 1960 tsunami generated in the same region by the great m w 9 5 1960 chilean earthquake both tsunamis were clearly observed on the coast of british columbia the 1960 tsunami was measured by 17 analog pen and paper tide gauges while the 2010 tsunami was measured by 11 modern digital coastal tide gauges four neptune canada bottom pressure recorders located offshore from southern vancouver island and two nearby open ocean dart stations the 2010 records were augmented by data from seven noaa tide gauges on the coast of washington state this study examines the principal characteristics of the waves from the 2010 event height period duration and arrival and travel times and compares these properties for the west coast of canada with corresponding properties of the 1960 tsunami results show that the 2010 waves were approximately 3 5 times smaller than the 1960 waves and reached the british columbia coast 1 h earlier the maximum 2010 wave heights were observed at port alberni 98 4 cm and winter harbour 68 3 cm the observed periods ranged from 12 min at port hardy to 110 120 min at prince rupert and port alberni and 150 min at bamfield the open ocean records had maximum wave heights of 6 11 cm and typical periods of 7 and 15 min coastal and open ocean tsunami records revealed persistent oscillations that rang for 3 4 days tsunami energy occupied a broad band of periods from 3 to 300 min estimation of the inverse celerity vectors from cross correlation analysis of the deep sea tsunami records shows that the tsunami waves underwent refraction as they approached the coast of vancouver island with the direction of the incoming waves changing from an initial direction of 340 true to a direction of 15 true for the second train of waves that arrived 7 h later after possible reflection from the marquesas and hawaiian islands

tsunami source of the 2004 sumatra andaman earthquake inferred from tide gauge and satellite data tsunami source of the 2004 sumatra andaman earthquake was esti mated from a joint inversion of tsunami waveforms recorded on tide gauges and sea surface heights captured by satellite altimetry measurements the earthquake the largest in the past 40 years caused devastating tsunami damage to countries around the indian ocean but the tsunami source in particular its northern end was not well resolved although aftershocks and crustal deformation extended from off north western sumatra island through the nicobar islands to the andaman islands some seismic wave analyses indicated a shorter source length several hundred kilometers we used tsunami waveforms recorded at 12 tide gauge stations around the source and the sea surface heights measured by three satellites jason1 topex poseidon and envisat we numerically computed tsunami propagation using realistic bathym etry more than 66 000 depth points were digitized from nautical charts and combined with the etopo2 data inversion of satellite data indicates that the tsunami source extended to the andaman islands with a total length of 1 400 km but such a model produces much larger tsunami waveforms than observed at indian tide gauge stations inversion of tide gauge records and the joint inversion indicate that the tsunami source was about 900 km long the largest slip about 13 to 25 m was located off sumatra island and the second largest slip up to 7 m near the nicobar islands the slip distribution is similar for different rupture velocities and rise times with a slow velocity of 1 km sec and a rise time of 3 min yielding the largest variance reduction

numerical tsunami simulation including elastic loading and seawater density stratification systemic discrepancies between observed and modeled tsunami wave speeds were previously identified for two recent major tsunamis the 2010 maule and 2011 tohoku events to account for these discrepancies we developed a numerical tsunami propagation code solving the shallow water equation and including the effects of elastic loading of the seafloor by the tsunami as well as a linear density profile in the seawater column we show here that both effects are important to explain the commonly observed difference between observations and simulations we conclude that the density variation in the seawater column affects the wave speed without changing the waveform whereas the loading effect has an effect on the wave speed and the waveform showing a negative phase before the main arrival due to the depression of the seafloor surrounding the tsunami wave the combination of both effects is needed to achieve a better match between observations and simulations

geomorphic effects of a large flood on fluvial fans the response of 12 fluvial fans near sydney australia to a large storm between 2 and 4 february 1990 was determined by repeating previously surveyed longitudinal profiles and by undertaking detailed field observations of erosion and deposition peak rainfall intensities occurred on 3 and 4 february when between 173 and 193 8 mm were recorded return periods for 24 h duration peak rainfall ranged between 5 7 and 11 0 years on the annual maximum series at six stations within the study area and return periods for 48 h peak rainfall ranged between 13 5 and 29 4 years of the 12 fans seven were trenched and five untrenched the most significant geomorphic effects of the storm were recorded on the proximal region of the fans however fan response was highly variable with one fan exhibiting no detectable change three fans localized deposition two fans spatially disjunct erosion and deposition two fans channel avulsions and seven fans fanhead trench reworking some fans exhibited more than one type of response a four stage tentative cyclical model of fanhead development was constructed from the field data stage 1 refers to the episodic aggradation of the fanhead by localized deposition spatially disjunct erosion and deposition and or channel avulsions stage 2 represents the initiation of a fanhead trench when progressive aggradation locally exceeds a threshold slope leading to localized erosion this erosion initially creates one or more discontinuous flow aligned scour pools over time the scour pools widen deepen and extend both up and downfan stage 3 refers to the coalescence of discontinuous scour pools into a continuous trench by the removal of intervening log and boulder steps stage 4 represents the backfilling phase of the trench once it has been overwidened and or slope reduced aggradation then continues as for stage one

topset dominated deltas a new model for river delta stratigraphy in the late 1800s g k gilbert provided the first stratigraphic description of river delta deposits but later work revealed that the gilbert type model long thought to be universal did not apply to all deltas here we propose that in addition to gilbert type deltas herein called foreset dominated there is a class of deltas with a basic first order stratigraphy that is topset dominated we develop a geometric model that predicts the occurrence of each delta type by calculating the topset and foreset thicknesses under different fluvial and basinal conditions our model predicts that topset dominated deltas have a novel characteristic their distributary channels commonly incise into pre delta sediment this type of delta should be common on shelves where the slope is less than 0 05 and the river feeding the delta has a discharge greater than 200 m 3 s field data from gulf of mexico deltas confirm the prediction that distributary channels often incise into pre delta sediment finally we propose a new stratigraphic model for topset dominated deltas and suggest that future stratigraphic interpretation must distinguish between delta types because the cause of channel incision for each is different and may be unrelated to allogenic changes

traveltime delay and initial phase reversal of distant tsunamis coupled with the self gravitating elastic earth systematic tsunami traveltime delays of up to 15 min relative to the numerically simulated long waves from the 2010 chilean and 2011 tohoku oki earthquakes were widely observed at deep ocean tsunamimeters enigmatic small negative phases appearing before the main peak were commonly found only at the trans oceanic locations the frequency dependence of the measured tsunami phase velocities shows reverse dispersions at long periods i e the tsunami speed becomes slower at periods beyond 1000 s this is consistent with the phase velocities of a tsunami mode coupled with a self gravitating elastic earth suggesting that the effects of compression and dilatation of seawater elastic tsunami loadings on a solid earth and the geopotential variations associated with the motion of mass during tsunami propagation are responsible for the traveltime delays and the initial negative phases simple 1 d tsunami propagation tests confirm that the reverse dispersion creates a small negative phase that precedes the main peak at large distances a new method to simulate tsunami waveforms on real ocean bathymetry that takes into account seawater compressibility the elasticity of the earth and geopotential perturbations has been developed by applying a phase correction to the simulated long waves the simulated waveforms in which phase corrections are applied for the dispersion effects accurately reproduce the observed waveforms including a small initial negative phase that appears at distant locations the traveltime difference between the observed and simulated waveforms has been decreased to less than 5 min and the waveform difference between them remarkably diminishes

a comparative study of far field tsunami amplitudes and ocean wide propagation properties insight from major trans pacific tsunamis of 2010 2015

modeling the densification of polar firn including heat diffusion application to close off characteristics and gas isotopic fractionation for antarctica and greenland sites 1 modeling the densification of polar firn is essential to estimate variations of close off characteristics density close off depth delta age in relation with past climate parameters temperature and accumulation rates furthermore the air composition in the firn is modified by gravitational and thermal fractionation and stable isotope measurements of permanent gases like nitrogen or argon can provide information on the amplitude of these fractionations in this work we propose a new model coupling firn densification and heat diffusion in addition to the determination of the firn thickness and gas ice age differences the model allows a reconstruction of the time evolution of the temperature for different sites in antarctica vostok and greenland gisp2 and therefore the evolution of gravitational and thermal isotopic fractionations in firn under present day conditions the modeled profiles are in good agreement with the available temperature measurements in firn for sites with low accumulation rates such as vostok the results show the existence of temperature gradients in the firn column even when no rapid climatic changes occur the comparison of the modeled 15n results to measurements allows to better constrain the 18o temperature relationship used to infer the surface temperature history and for gisp2 the model validates the long term borehole based temperature

dispersion and nonlinear effects in the 2011 tohoku oki earthquake tsunami this study reveals the roles of the wave dispersion and nonlinear effects for the 2011 tohoku oki earthquake tsunami we conducted tsunami simulations based on the nonlinear dispersive equations with a high resolution source model the simulations successfully reproduced the waveforms recorded in the offshore deep sea and focal areas the calculated inundation area coincided well with the actual inundation for the sendai plain which was the widest inundation area during this event by conducting sets of simulations with different tsunami equations we obtained the followings insights into the wave dispersion nonlinear effects and energy dissipation for this event although the wave dispersion was neglected in most studies the maximum amplitude was significantly overestimated in the deep sea if the dispersion was not included the waveform observed at the station with the largest tsunami height 2 m among the deep ocean stations also verified the necessity of the dispersion it is well known that the nonlinear effects play an important role for the propagation of a tsunami into bays and harbors additionally nonlinear effects need to be considered to accurately model later waves even for offshore stations in particular including nonlinear terms rather than the inundation was more important when precisely modeling the waves reflected from the coast

autogenic response of alluvial bedrock transition to base level variation experiment and theory 1 short term autogenic processes are thought to be averaged out by long term allogenic forcing and have often been ruled out in stratigraphic interpretation it is generally difficult to resolve the scale of autogenic effects on landscape evolution and even more so on sedimentary records here we analyze short term variation in migration rate of the alluvial bedrock transition in a series of experiments the experiments developed a fan delta over a stationary sloped nonerodible basement with constant water and sediment discharges the rate of base level change varies between experiments but was constant for a given experiment the location of the alluvial bedrock transition varied autogenically in all experiments the instantaneous migration rate of the alluvial bedrock transition varied by as much as an order of magnitude more than that induced by allogenic forcing the strong autogenic pulses can be explained by sediment storage and release due to intrinsic variation in the transport efficiency of the fluvial system data from experiments with base level change indicate that the autogenic signal in the migrating alluvial bedrock transition is weakest during landward migration onlap when base level rises and strongest during basinward migration valley incision when base level falls we use a one dimensional geometric model to explain the variations in the autogenic response of the alluvial bedrock transition as a function of direction of base level change the model periodically changes fluvial slope to represent the effects of sediment storage and release with base level rise and fall the modeling result reproduces the observed pattern of autogenic variation in alluvial bedrock transition

mechanics of river mouth bar formation implications for the morphodynamics of delta distributary networks 1 in this paper we use observational data and numerical modeling to present a new explanation for the formation of river dominated delta networks observational data from deltas throughout the world show that distributary channel widths depths and lengths decrease nonlinearly with successive bifurcations trends in width and depth are an outcome of hydraulic geometry scaling the trend in channel length is a consequence of delta growth analyses of serial maps show that the positions of bifurcations are the fossilized locations of river mouth bars also called middle ground and distributary mouth bar in front of old delta channel mouths therefore the trend in channel length can be explained through the mechanics of river mouth bar formation and evolution we use delft3d a coupled hydrodynamic and morphodynamic model to simulate the process of river mouth bar formation within an expanding turbulent jet in front of distributary channel mouths our results describe in detail the formation and evolution of a river mouth bar system and demonstrate that the distance to the river mouth bar is proportional to jet momentum flux and inversely proportional to grain size therefore channel length decreases down delta because with each successive bifurcation the jet momentum flux decreases these results can be used to predict the future evolution of river dominated deltas and can be used to aid in hydrocarbon exploration of these depositional environments

large scale fluvial grade as a nonequilibrium state in linked depositional systems theory and experiment 1 a graded river conveys its sediment load without net aggradation or degradation grade is thought to represent the equilibrium state of a river system subject to steady allogenic forcing we address the concept of grade in linked depositional systems through a combination of mathematical modeling and flume experiments we develop a moving boundary morphodynamic model of fluviodeltaic sedimentation and use it to quantify the conditions necessary for a state of sustained grade in an alluvial deltaic system developing on a uniformly sloping shelf to test our theory we conducted a series of flume experiments in which we constructed laboratory scale fluviodeltaic systems under specific relative sea level histories on large spatiotemporal scales our theoretical and experimental results suggest an alternative view of grade as an intrinsically nonequilibrium state that requires a fall in relative sea level under conditions of stillstand or rise in relative sea level the equilibrium graded profile does not exist and the alluvial river will always aggrade with a steady sediment supply alluvial grade can be sustained if relative sea level falls with a specific square root of time dependence common sequence stratigraphic conceptualizations of alluvial river response to sea level change suggest that rivers aggrade and degrade in response to relative sea level rise and fall respectively we show that rivers can remain aggradational if the rate of sea level fall is sufficiently small the boundary between aggradational and degradational states is the graded state described here that associated with a relative sea level fall that varies with the square root of time

autostratigraphy a framework norm for genetic stratigraphy abstract autostratigraphy is the stratigraphy generated by large scale autogenic processes and needs to be heeded because of a current overreliance on allogenic controls in sequence stratigraphy key principles of autostratigraphy emerging from the theory of autoretreat and a new understanding of alluvial grade derive from the non equilibrium stratigraphic response i e the general lack of equilibrium configuration of depositional systems the non equilibrium behavior of fluvial deltas during times t of steady dynamic forcing leads to variable stratigraphic response that is the inevitable result of length d and time scaling particular to the depositional system rather than necessarily reflecting any sudden or unsteady change in the rate of allogenic forcing some abrupt breaks in the stratigraphic record are not necessarily associated with changes in allogenic conditions but can result from purely autogenic processes of the system when t is comparable to or longer than 1 the depositional system takes the non equilibrium large scale autogenic response 2 the superposition of autogenic and allogenic components of the forcing is prominently nonlinear and thus 3 sequence stratigraphic models that have been built on the assumption of equilibrium response are incorrect autostratigraphic analysis makes it possible to detect and identify complex autogenic responses and unsteady allogenic events in the stratigraphic record by quantifying a temporal change in the magnitude of d autostratigraphy thus functions as a norm for genetic stratigraphy

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

the 26 december 2004 sumatra tsunami analysis of tide gauge data from the world ocean part 1 indian ocean and south africa the m w 9 3 megathrust earthquake of december 26 2004 off the northwest coast of sumatra in the indian ocean generated a catastrophic tsunami that was recorded by a large number of tide gauges throughout the world ocean part 1 of our study of this event examines tide gauge measurements from the indian ocean region at sites located from a few hundred to several thousand kilometers from the source area statistical characteristics of the tsunami waves including wave height duration and arrival time are determined along with spectral properties of the tsunami records

the global reach of the 26 december 2004 sumatra tsunami numerical model simulations combined with tide gauge and satellite altimetry data reveal that wave amplitudes directionality and global propagation patterns of the 26 december 2004 sumatra tsunami were primarily determined by the orientation and intensity of the offshore seismic line source and subsequently by the trapping effect of mid ocean ridge topographic waveguides

climate of the last 500 years high resolution ice core records precipitation accumulating on the earth s ice sheets and ice caps records a variety of physical and chemical information about the atmosphere and in some cases provides unique insight to both the history and the mechanics of the earth s environmental system high resolution well dated dust records from both polar ice sheets suggest a linkage between increased atmospheric dust and cooler temperatures over antarctica but a similar relationship is not observed in ice cores from either greenland or china net accumulation histories for the last 490 years reveal no discemible global pattern although interesting regional differences and similarities exist excess non sea salt sulfate profiles provide

the december 2018 anak krakatau volcano tsunami as inferred from post tsunami field surveys and spectral analysis we present analysis of the december 2018 anak krakatau tsunami in sunda strait indonesia from a combination of post tsunami field surveys bathymetric changes and spectral analysis of the tsunami tide gauge records post tsunami surveys revealed moderate tsunami height along the coast of sumatra and java with maximum surveyed runup of 13 5 m and maximum inundation distance of 330 m at small islands located close to the volcano extreme tsunami impacts were observed indicating not only a huge tsunami was generated by large amounts of collapse material which caused notable changes of seafloor bathymetry but also indicates the role of those small islands in reducing tsunami height that propagated to the mainland of indonesia our spectral analysis of tide gauge records showed that the tsunami s dominant period was 6 6 7 4 min indicating the short period nature of the 2018 sunda strait tsunami

autocyclic behaviour of fan deltas an analogue experimental study fan deltas are excellent recorders of fan building processes because of their high sedimentation rate particularly in tectonically active settings although previous research focuses mainly on allogenic controls there is clear evidence for autogenically produced storage and release of sediment by flume and numerical modelling that demands further definition of characteristics and significance of autogenically forced facies and stratigraphy analogue experiments were performed on fan deltas with constant extrinsic variables discharge sediment supply sea level and basin relief to demonstrate that fan delta evolution consists of prominent cyclic alternations of channellized flow and sheet flow the channellized flow is initiated by slope induced scouring and subsequent headward erosion to form a channel that connected with the valley while the removed sediment is deposited in a rapidly prograding delta lobe the resulting decrease in channel gradient causes a reduction in flow strength mouth bar formation flow bifurcation and progressive backfilling of the channel in the final stage of channel filling sheet flow coexists for a while with channellized flow semi confined flow although in cycle 1 this phase of semi confined flow was absent subsequent autocyclic incisions are very similar in morphology and gradient however they erode deeper into the delta plain and as a result take more time to backfill the duration of the semi confined flow increases with each subsequent cycle during the period of sheet flow the delta plain aggrades up to the critical gradient required for the initiation of autocyclic incision this critical gradient is dependent on the sediment transport capacity defined by the input conditions these autogenic cycles of erosion and aggradation confirm earlier findings that storage and release of sediment and associated slope variation play an important role in fan delta evolution the erosional surfaces produced by the autocyclic incisions are well preserved by the backfilling process in the deposits of the fan deltas these erosional surfaces can easily be misinterpreted as climate sea level or tectonically produced bounding surfaces

alluvial fans formed by channelized fluvial and sheet flow ii application the formulation of the companion paper describing the evolution of mean elevation in a radially symmetric alluvial fan is applied to the specific case of the tailings basin of an iron mine the tailings basin provides a simple field scale example of a fluvial fan delta system calculation procedures are developed to determine the effect of changing water and sediment discharge on fan evolution the analysis is used to evaluate options for the extension of the lifetime of the tailings basin

channel dynamics sediment transport and the slope of alluvial fans experimental study a b s t ra c t we present the results of an experimental study of alluvial fan sedimentation under conditions of constant inflow water discharge qw sediment supply qso and median grain size d the study was designed to complement and test a recently formulated model of alluvial fan sedimentation and to emphasize the interactions between and controls on flow channelization and equilibrium fan slope flow channelization and fan sedimentation were studied under conditions of nearly steady uniform aggradation steady conditions were achieved by imposing a steadily rising base level just in balance with the average sediment aggradation rate experimental inflows covered a wide range of conditions allowing examination of the effects of variations in qw q so and d in both bedload and suspension dominated environments experimental results were most consistent with an expanding flow channel model key experimental findings successfully and quantitatively predicted by the expanding flow theory include 1 straight to slightly concave radial profiles of bedload dominated fans 2 distinctly convexo concave profiles of suspension dominated fans 3 a strong inverse relationship between qw and fan slope 4 a strong but secondary relationship between q so and fan slope and 5 near independence of d and fan slope so long as transport stage is high and bedload transport dominant however potential scale effects in the experiments arose from reduced flow reynolds numbers and incorrect geometric scaling of channel widths no confident conclusions regarding the debate over the relative importance of sheetfloods and braided channel flows can be drawn from the experimental data extrapolation to field scale is best accomplished through appropriate application of the theoretical model herein confirmed against experimental data

modeling deltaic lobe building cycles and channel avulsions for the yellow river delta china river deltas grow by repeating cycles of lobe development punctuated by channel avulsions so that over time lobes amalgamate to produce a composite landform existing models have shown that backwater hydrodynamics are important in avulsion dynamics but the effect of lobe progradation on avulsion frequency and location has yet to be explored herein a quasi 2 d numerical model incorporating channel avulsion and lobe development cycles is developed the model is validated by the well constrained case of a prograding lobe on the yellow river delta china it is determined that with lobe progradation avulsion frequency decreases and avulsion length increases relative to conditions where a delta lobe does not prograde lobe progradation lowers the channel bed gradient which results in channel aggradation over the delta topset that is focused farther upstream shifting the avulsion location upstream furthermore the frequency and location of channel avulsions are sensitive to the threshold in channel bed superelevation that triggers an avulsion for example avulsions occur less frequently with a larger superelevation threshold resulting in greater lobe progradation and avulsions that occur farther upstream when the delta lobe length prior to avulsion is a moderate fraction of the backwater length 0 3 0 5l b the interplay between variable water discharge and lobe progradation together set the avulsion location and a model capturing both processes is necessary to predict avulsion timing and location while this study is validated by data from the yellow river delta the numerical framework is rooted in physical relationships and can therefore be extended to other deltaic systems

field survey of the march 28 2005 nias simeulue earthquake and tsunami on the evening of march 28 2005 at 11 09 p m local time 16 09 utc a large earthquake occurred offshore of west sumatra indonesia with a moment magnitude mw of 8 6 the event caused substantial shaking damage and land level changes between simeulue island in the north and the batu islands in the south the earthquake also generated a tsunami which was observed throughout the source region as well as on distant tide gauges while the tsunami was not as extreme as the tsunami of december 26th 2004 it did cause significant flooding and damage at some locations the spatial and temporal proximity of the two events led to a unique set of observational data from the earthquake and tsunami as well as insights relevant to tsunami hazard planning and education efforts

history and features of trans oceanic tsunamis and implications for paleo tsunami studies abstract far field tsunamis and their features as well as methods to quantify trans oceanic tsunamis are reviewed with examples of instrumental and historical data tsunamis from the 1854 nankai earthquakes the 1946 aleutian tsunami earthquake the 1960 and 2010 chile earthquakes as well as the 2011 tohoku earthquake were recorded around the pacific ocean the 1883 krakatoa volcanic eruption caused volcanic tsunami in the indian ocean and meteotsunami in the pacific ocean the 2004 indian ocean tsunami was also recorded in the pacific ocean when a tsunami amplitude is larger than that of ocean tides which usually requires the parent earthquake to be gigantic mw 9 it can cause damage and may be historically documented the trans pacific tsunamis described in historical documents include those from the 1700 cascadia earthquake the 1730 1751 1837 and 1877 earthquakes off chile and the 1687 and 1868 earthquakes off peru the tsunami record in japan from the 1586 peru earthquakes was found to be incorrect and should be discounted the tsunami magnitude scale relates the tsunami heights to the earthquake size tsunami travel time can be computed from actual bathymetry and the tsunami ray tracing provides relative amplitudes due to focusing defocusing caused by irregular bathymetry numerical computations from fault models produce tsunami amplitudes and waveforms and indicate strong directivity due to strike of fault or orientation of subduction zones far field tsunamis are often long lasting due to multiple reflections across the basin or on continental shelf or due to resonance in bays harbors these features would provide important criteria to estimate tsunami sources from paleo tsunami data

origin of a preferential avulsion node on lowland river deltas river deltas are built by cycles of lobe growth and abrupt channel shifts or avulsions that occur within the backwater zone of coastal rivers previous numerical models differ on the origin of backwater scaled avulsion nodes and their consistency with experimental data to unify previous work we developed a numerical model of delta growth that includes backwater hydrodynamics river mouth progradation relative sea level rise variable flow regimes and cycles of lobe growth abandonment and reoccupation for parameter space applicable to lowland deltas we found that flow variability is the primary mechanism to cause persistent avulsion nodes by focusing aggradation within the backwater zone backwater scaled avulsion nodes also occur under less likely scenarios of initially uniform bed slopes or during rapid relative sea level rise and marine transgression our findings suggest that flow variability is a fundamental control on long term delta morphodynamics

palaeoflow reconstruction from fan delta morphology on mars abstract alluvial fans and deltas on mars record past hydrological conditions until now these conditions have been inferred from the morphology of the feeder channels and the deposits from images and digital terrain models dtms and from calculations of the bulk fluxes of water and sediment based on the dimensions of upstream channels neither method can distinguish between dilute river like flows and dense sediment laden flows however while the formation time scales for these two sediment transport modes differ by orders of magnitude the objective of this paper is to compare dtm data quantitatively with a morphological model to infer sediment transport mode and formative duration we present a quantitative morphological model for fan and delta formation that assumes as little as possible the model calculates the growth of a sedimentary body in a crater lake represented by a low gradient subaerial cone on top of a high gradient subaqueous cone the volume of the cone is constrained by the influx of sediment while the elevation of the break in slope that is the shoreline is constrained by the influx of water the water and sediment fluxes were calculated with physics based predictors based on the feeder channel small scale morphology such as crater wall irregularities concavity of the fan surface and channel avulsion is ignored the model produces alluvial fans stair stepped fan deltas and gilbert fan deltas as well as hitherto unidentified crater wall drapes the parameters that determine which morphology emerges are the supply of sediment and water to the basin the size of the basin and the duration of the flow a direct comparison between the cone model and hrsc dtm data for five deltas and an alluvial fan demonstrates that single event dilute flows of short duration days to years have created all of the deposits two gilbert fan deltas were formed in overspilling crater lakes from long low gradient upstream channels one alluvial fan was formed in a similar manner except that the damaged crater did not lead to ponding three stair stepped deltas were formed from short high gradient upstream channels that only partially filled the crater lakes

new insights into the source of the makran tsunami of 27 november 1945 from tsunami waveforms and coastal deformation data we constrain the source of the 27 november 1945 tsunami in the makran subduction zone msz using available tsunami waveforms recorded on tide gauges at mumbai india and karachi pakistan and that inferred at port victoria seychelles and coseismic deformation data along the makran coast spectral analysis of the tsunami waveforms shows that the tsunami governing period was 40 50 min at karachi whereas it was around 22 min at mumbai the inferred tsunami waveform at port victoria also indicated a period of around 21 min for the tsunami tsunami numerical simulations from the previously proposed source models failed in reproducing the observed tsunami waveforms and coseismic deformation data sensitivity analysis showed that the source fault needs to be extended offshore into deep water in order to reproduce the first 22 min signal at mumbai based on the inversion of the observed tsunami waveforms we propose a four segment fault with varying slip amounts as the final source this source includes a slip of 4 3 m onshore near ormara pakistan and a slip of 10 m offshore at water depth of around 3 000 m the total fault length is 220 km and the average slip is 6 1 m this source first reproduces fairly well the observed tide gauge records at mumbai and karachi second produces 1 m of uplift at ormara and 1 m of subsidence at pasni and third gives a moment magnitude of 8 3 for the earthquake which is in the acceptable range of seismic data the computed 1 m uplift at ormara is in the uplift range of 1 3 m reported in the literature as the tide gauge stations were located in the far field our proposed source explains mainly the tectonic source of the tsunami

the pulse of calm fan deltas abstract at the heart of interpreting the history of earth surface evolution preserved in the rock record is distinguishing environmental allogenic forcing from internally generated autogenic noise allogenic deposits classically have been recognized by their cyclic nature which apparently results from periodic changes in base level sediment supply or tectonics autogenic deposits which are quite variable in their origin and scale are caused by the nonlinearity of sediment transport and might be expected to have a random or scale free fractal signature here we describe a robust mechanism that generates cyclic deposits by an autogenic process in experimental fan deltas sheet flow over the fan surface induces deposition and an increase in fluvial slope and curvature to a point where the surface geometry is susceptible to a channelization instability similar to channel initiation on hillslopes channelized flow results in incision and degrading of the fan surface to a lower slope releasing a

tsunami impact computed from offshore modeling and coastal amplification laws insights from the 2004 indian ocean tsunami the 2004 indian ocean tsunami gave the opportunity to gather unprecedented tsunami observation databases for various coastlines we present here an analysis of such databases gathered for 3 coastlines among the most impacted in 2004 in the intermediate and far field thailand myanmar se india sri lanka and se madagascar non linear shallow water tsunami modeling performed on a single 4 coarse bathymetric grid is compared to these observations in order to check to which extent a simple approach based on the usual energy conservation laws either green s or synolakis laws can explain the data the idea is to fit tsunami data with numerical modeling carried out without any refined coastal bathymetry topography to this end several parameters are discussed namely the bathymetric depth to which model results must be extrapolated using the green s law or the mean bathymetric slope to consider near the studied coast when using the synolakis law using extrapolation depths from 1 to 10 m generally allows a good fit however a 0 1 m is required for some others especially in the far field madagascar possibly due to enhanced numerical dispersion such a method also allows describing the tsunami impact variability along a given coastline then using a series of scenarios we propose a preliminary statistical assessment of tsunami impact for a given earthquake magnitude along the indonesian subduction conversely the sources mostly contributing to a specific hazard can also be mapped onto the sources providing a first order definition of which sources are threatening the 3 studied coastlines

the updip seismic aseismic transition of the sumatra megathrust illuminated by aftershocks of the 2004 aceh andaman and 2005 nias events great subduction earthquakes exhibit segmentation both within the rupture of individual events and in the long term history of the margin the 2004 december 26 aceh andaman and 2005 march 28 nias event in northern sumatra are two of the largest earthquakes in recent years with both co and post seismic displacements constrained in unprecedented detail using aftershock locations from a temporary seismic array in the boundary region between both events and waveform modelling of large aftershocks we demonstrate that the vast majority of aftershocks in the study region occur on the plate interface within a narrow band 20 km seaward of the outer arc high comparing the seismicity distribution to the co and post seismic displacements we infer that the seismic band marks the transition between the seismogenic zone and stable sliding the location of the band and therefore the transition appears to be correlated with the 500 m bathymetry contour this close correspondence is disrupted at the boundary between the two great earthquakes where the transition to seismogenic behaviour occurs further landward by 25 km to the west of simeulue where seafloor bathymetry throughout the forearc is deeper than 500 m the seismic band terminates abruptly and the focus of aftershock activity is found near the trench the seismic efficiency of afterslip varies dramatically along strike the segment below the banyak islands in the gap between the two main asperities of the nias earthquake accommodates a much larger proportion of afterslip seismically