the vertical structure of shadow zone arrivals at long range in the ocean multimegameter range acoustic data obtained by bottom mounted sosus receivers show significant acoustic energy penetrating several hundred meters into the geometric shadow zones below cusps in the predicted acoustic time fronts much further than can be accounted for by diffraction dushaw et al ieee j oceanic eng 24 202 214 1999 acoustic data from two vertical line array receivers deployed in close proximity in the north pacific ocean together virtually spanning the water column show similar shadow zone arrivals for transmissions from broadband 250 hz sources moored at the sound channel axis 750 m and at surface conjugate depth 3000 m at ranges of 500 and 1000 km the vertical structure of the receptions will be compared to parabolic equation propagation simulations for sound speed fields constructed from high resolution underway conductivity temperature depth uctd data in the upper 400 m widely spaced deep ctd casts and climatological data predictions will be made i for the observed field ii for a smoothed field and iii for fields that include sound speed fines structure due to density variations internal waves or due to density compensated sound speed variations spice

the use of one and two dimensional hydraulic modelling to reconstruct a glacial outburst flood in a steep alpine valley the hydrologic characteristics of the 1943 outburst flood from the glacier du mont mine switzerland are herein reconstructed using field evidence palaeostage indicators in conjunction with shallow water modelling techniques these techniques rely on accurately characterising the hydraulic roughness of the channel the water height established as boundary conditions and the main flow path during the former flood but the selection of appropriate parameter values can be problematic and hence there is uncertainty in the estimated discharge in this study minimal flow discharge estimates derived from one dimensional modelling were found to vary between 429 and 557 m3 s 1 as the hydraulic roughness ks and water height at the inlet were varied over a realistic range of values 0 8 1 4 m and 3 31 6 m respectively whereas flow rates derived via two dimensional modelling were confined in a narrower lower range of 358 454 m3 s 1 this degree of sensitivity to bed roughness ks boundary conditions and the spatial dimensions of the modelling approach is for the one dimensional modelling higher than reported in previous studies but the precision of flow discharge values reconstructed using the two dimensional modelling approach appears to be acceptable even for floods in the very steep valley 0 1 m m that is subject of this study

quasiperiodic southward moving waves in 630 nm airglow images in the equatorial thermosphere 1 we report quasiperiodic southward moving waves which are commonly observed in the oi 630 nm airglow images emission altitudes of 200 300 km near the equator in 2 year airglow observations at kototabang indonesia 0 2 s 100 3 e geomagnetic latitude of 10 4 the waves have predominantly east west phase fronts and repeatedly propagate southward with a velocity of 310 110 m s and a period of 40 15 min they are frequently observed in may july with an occurrence rate of 53 and are also observed in other seasons with occurrences of 20 the waves are observed in and to the south geomagnetically poleward of the equatorial ionospheric anomaly which is identified as an airglow enhancement region moving gradually to lower geomagnetic latitudes at the premidnight local times we suggest that gravity waves in the lower thermosphere below 300 km are a plausible cause of the observed quasiperiodic waves in the airglow images

palaeoshorelines of glacial lake kuray chuja south central siberia form sediments and process glacial lake kuray chuja which occupied the kuray and chuja basins during the quaternary period marine isotope stages 2 and 3 left distinct shoreline features around the basin margins at the greatest extent the lake had a surface area of 2951 km2 with wind fetches up to 70 km wind waves constructed erosional erosional accumulative and accumulative strandlines the latter including spits tombolos barrier beaches and offshore bars strandlines range in altitude between c 1600 and 2100 m the range in altitudes demonstrating lake level variations through time the shoreline forms and stratigraphy are detailed particular attention is given to the presence of pocket beaches on rock coasts the alluvial strandlines of which have distinctive alongshore gradients although reasonably ascribed to regional differential tectonic uplift the possibility that the local alongshore gradients are augmented as a process response to alongshore drift of sediment in a sediment starved system of closed coastal cells is explored using a simple numerical model

sedimentary effects of cataclysmic late pleistocene glacial outburst flooding altay mountains siberia rudoy a n and baker v r 1993 sedimentary effects of cataclysmic late pleistocene glacial outburst flooding altay mountains siberia in c r fielding editor current research in fluvial sedimentology sediment geol 85 53 62 pleistocene glacial outburst floods were released from ice dammed lakes of the altay mountains south central siberia the kuray chuja lake system yielded peak floods in excess of 1 106 m 3 s 1 and as great as 18 106 m 3 s i the phenomenally high bed shear stresses and stream powers generated in these flows produced a main channel coarse grained facies of coarse gravel in 1 foreset bedded bars as much as 200 m high and several kilometers long and 2 degradational boulder capped river terraces giant current ripples 50 to 150 m in spacing composed of pebble and cobble gravel are locally abundant the whole sedimentary assemblage is very similar to that of the channeled scabland produced by the pleistocene missoula floods of western north america

paleohydraulic reconstruction of the largest glacial lake missoula draining s glacial lake missoula glm was the source of earth s largest known peak flood discharges onto the channeled scabland northwestern united states the original studies of glm were based on geomorphological mapping of lake sediments and shorelines more recently studies have emphasized the computational fluid dynamics of downstream megaflood routing and characteristics in the channeled scabland and adjacent areas however actual details of the lake draining processes glm have received little scientific attention in this paper we employ two dimensional hydraulic modelling to understand the paleoflow conditions for different scenarios of draining glm at its highest stands values are calculated for three glm drainage hydrographs 2 6 13 17 10 6 m 3 s 1 that previous studies had estimated for outlet flows consistent with regional mapping and with the original interpretation of fluvial geomorphology by other studies the modelling shows that lake silt sequences in the gorges of glm must postdate the most highly energetic outburst events from the lake this is because the flows generated in the lake by megaflood outflows are sufficiently energetic to erode any accumulated silt deposits in contrast the gravels underlying the silts in these zones include boulder sized clasts largescale cross stratification and 70e100 m high bars forms all of which indicate very high energy flood flow conditions the modelling also shows that the paleohydraulic conditions which developed in the lake basin during the largest megaflood outflows would be capable of accounting for the observed bedrock scour at rainbow lake pass various high eddy deposits eddy bars of flood gravel in gorges and the giant ripple marks subaqueous gravel dunes that were classically described in the 1940s previous studies interpreted the glacial lake silt rhythmites and related deposits such as the ninemile section as evidence for numerous fillings and drainings of glm our modelling suggests that these inferred events must have been relatively low in energy and magnitude relative to the earlier outburst s that emplaced the flood gravels subaqueous gravel dunes and scabland like erosion surfaces

super medium scale traveling ionospheric disturbance observed at midlatitude during the geomagnetic storm on 10 november 2004 1 medium scale traveling ionospheric disturbances mstids whose peak to peak amplitude was larger than 20 tecu 1016el m2 were observed at midlatitude during the geomagnetic storm on 10 november 2004 this amplitude was more than 10 times larger than that of the average mstid high resolution data of the gps earth observation network geonet clarified the characteristic of the total electron content tec disturbances over japan on 10 november 2004 the disturbances started around 1000 ut in the central part of japan the maximum of tec temporal change was 7 2 tecu in 30 s the disturbances had several wave fronts which extended from northwest to southeast and propagated from northeast to southwest tec data around japan revealed that the disturbances were mainly observed from 18 n s to 34 n s of the geomagnetic latitude in the both hemispheres since those characteristics were similar to those of mstids in spite of the unusual large amplitude the mstids are referred as super mstids in this paper tec variations of the super mstids were also observed at 460 km altitude by the grace satellite the ion density fluctuations of the super mstids were observed in situ by the champ and dmsp f15 satellites which flew at 360 km and 850 km respectively it is found that the plasma density variations of the super mstids occurred mainly above 360 km altitude the characteristics that distinguish the event from plasma bubbles are its successive wave fronts constant northwest southeast direction along which the wave fronts stretched and late local time of the occurrence it is found that the uplift of the ionosphere around sunset excited the super mstids at midlatitudes the uplift was attributed to the strong eastward electric field during the geomagnetic storm

observations of gw tid oscillations in the f2 layer at low latitude during high and low solar activity geomagnetic quiet and disturbed periods 1 ionospheric vertical sounding observations using a digital ionosonde are being carried out on a routine basis at sao jose dos campos 23 2 s 45 9 w dip latitude 17 6 s hereafter referred to as sjc brazil located under the southern crest of the equatorial ionization anomaly eia since august 2000 in this paper we present and discuss the seasonal variation of gravity wave gw and traveling ionospheric disturbance tid oscillations in the ionospheric f2 layer during high solar activity hsa september 2000 to august 2001 and low solar activity lsa january 2006 to december 2006 observed at sjc during different levels of geomagnetic activity the gw tid signatures in the f2 layer can be seen in the isofrequency lines of virtual height daily variations for six fixed frequencies 3 4 5 6 7 and 8 mhz which show quasiperiodic oscillations crests and valleys the crests and valleys when seen in close frequencies present a phase difference i e first it is observed at higher frequency then at lower frequency indicating a downward phase velocity these quasiperiodic oscillations induced in the virtual heights are divided into three groups as small amplitude lower than 40 km medium amplitude between 40 km and 60 km and large amplitude greater than 60 km the observations show that gws tids are much more pronounced at f layer heights during hsa than lsa and the large amplitude gws tids are present normally only during hsa

is hydrology kinematic a wide range of phenomena natural as well as man made in physical chemical and biological hydrology exhibit characteristics similar to those of kinematic waves the question we ask is can these phenomena be described using the theory of kinematic waves since the range of phenomena is wide another question we ask is how prevalent are kinematic waves if they are widely pervasive does that mean hydrology is kinematic or close to it this paper addresses these issues which are perceived to be fundamental to advancing the state of the art of water science and engineering copyright 2002 john wiley sons ltd

freshwater megaflood sedimentation what can we learn about generic processes abstract there is growing recognition that sedimentary deposits related to high energy large scale freshwater floods are widespread across the continents and in the main can be related to quaternary outbreak flows from ice dammed lakes such deposits may also occur in the neogene and earlier recognition of these megaflood deposits is hindered by the lack of well conditioned stratigraphic models of depositional successions however descriptions of successions from many locations often exhibit commonalities when compared carefully thus the primary purpose of this paper is to examine and condense the published stratigraphic and sedimentological evidence so as to identify the key signatures of megaflood successions the deposits often are the only record of a flood and so the secondary purpose is to interpret the sedimentary sequences in order to recreate the behaviour of floods through single and multiple events finally some pointers are provided as to those areas of sedimentological research that might be profitably explored in more depth to improve understanding of megaflood dynamics a key characteristic of megaflood deposits is the apparent massive appearance of single units which on closer inspection usually are amalgamated layers of similar grain size distribution individual beds and sets of beds are commonly near horizontal planar and laterally extensive successions evidently are not channelized and extensivity is indicative of simultaneous and coherent deposition over large areas localised large scale clinoforms or smaller scale cross beds are common associated with bar front or dune progradation respectively but otherwise extensivity implies that cross cutting erosional contacts notably steeply inclined examples and small scale scours are not common except immediately around large isolated clasts such as dropstones and ice blocks a common vertical stack of sequences in any one succession consists of 1 basal thick coarse parallel bedded units 2 large scale clinoforms 3 horizontally bedded thin laminated units 4 ripple and dune cross beds 5 silt beds and 6 succession capping debris flow deposits in some cases such a succession usually is indicative of a single cycle of waxing and waning flood flow generally dominated by high concentration suspension deposition onto plane beds the high power allows the transport of fine gravel and coarse sand in suspension leading upon deposition to relatively coarse beds from suspension fall out clay and silt is generally sparse or absent being transported further down the system at the scale of the hydrograph the successions indicate that flows initially accelerate and then decelerate with significant shorter period flow pulses also evident in the sedimentary signatures in parallel bedded sequences primarily during waxing flows bedload transport often was ineffective in sorting sediment due to the high rates of deposition from the highly sediment charged waters resulting in diffuse accretion surfaces at each location similar sequence stacks are common leading to the impression of rhythmic deposition from pulsing flow including from repetitive series of floods although often composed of coarse grains many sequence stacks excluding any debris flows are not dissimilar to turbidity flow sequences the bouma sequence in particular although there is limited experimental evidence for turbidity currents associated with high energy freshwater flows theory does not preclude the deposition of similar sedimentary motifs from high concentration flows such that an analogy between some megaflood sedimentary beds and turbidites is not unreasonable despite considerable variation in megaflood sedimentary successions commonalities occur which are indicative of similar processes of deposition from high energy floods at geographically different locations the changes in style of deposition throughout a succession provide clues as to the nature of the flood flows and this information could be used to improve estimates of flood hydrograph behaviour however hypotheses linking deposit characteristics to flow dynamics are currently ill conditioned and often poorly tested the majority of published studies describe the coarser scale stratigraphy with only passing reference to the fine scale structure of individual beds closer attention to lamination styles particle orientation and syn depositional deformation structures for example should provide information on the flow mechanics at the time of bed deposition thus better consideration of the sedimentology of megaflood deposit beds will lead to better understanding of the controlling hydraulics and should result in better models of flood deposition

simulations of cataclysmic outburst floods from pleistocene glacial lake missoula using a flow domain that we constructed from 30 m digital elevation model data of western united states and canada and a two dimensional numerical model for shallow water flow over rugged terrain we simulated outburst floods from pleistocene glacial lake missoula we modeled a large but not the largest flood using initial lake elevation at 1250 m instead of 1285 m rupture of the ice dam centered on modern lake pend oreille catastrophically floods eastern washington and rapidly fills the broad pasco yakima and umatilla basins maximum flood stage is reached in pasco and yakima basins 38 h after the dam break whereas maximum flood stage in umatilla basin occurs 17 h later drainage of these basins through narrow columbia gorge takes an additional 445 h for this modeled flood peak discharges in eastern washington range from 10 to 20 10 6 m 3 s however constrictions in columbia gorge limit peak discharges to 6 m 3 s and greatly extend the duration of flooding we compare these model results with field observations of scabland distribution and high water indicators our model predictions of the locations of maximum scour product of bed shear stress and average flow velocity match the distribution of existing scablands we compare model peak stages to high water indicators from the rathdrum spokane valley walulla gap and along columbia gorge though peak stages from this less than maximal flood model attain or exceed peak stage indicators along rathdrum spokane valley and along columbia gorge simulated peak stages near walulla gap are 10 40 m below observed peak stage indicators despite this discrepancy our match to field observations in most of the region indicates that additional sources of water other than glacial lake missoula are not required to explain the missoula floods

possible evidence of gravity wave coupling into the mid latitude f region ionosphere during the seek campaign on five of eight observation nights during the 1996 seek sporadic e experiment over kyushu campaign japan unusual wave like structures were imaged in the 630 nm thermospheric nightglow emis sion four of these events were observed to travel to wards the southwest providing new evidence in support of recent theories describing the coupling of medium scale gravity waves into the mid latitude f region iono sphere available ionosonde data and the visual charac teristics of the wave structures indicate no association

subaqueous gravel dunes abstract gravel dunes are rarely reported owing to comparative rarity of occurrence and generic confusion with antidunes and classes of gravel bars a compilation of data from the literature for sediments with a median size greater than 2 mm shows that dunes have been developed in the laboratory in median grain sizes up to 28 6 mm for field conditions there are data for grain sizes up to 60 mm equilibrium and non equilibrium gravel dunes range in length from less than 0 6 m to greater than 100 m heights range from less than 0 1 m to 16 m height and length data for the steepest three dimensional 3 d gravel dunes are consistent with the h l function reported by ashley 1990 for equilibrium dunes developed in sand for a broad range of dune length 3 d gravel dunes are steeper than two dimensional 2 d dunes but for l 100 m and h 8 m there are too few data to draw any conclusion ashley s h l function does not apply to a broad range of 2 d gravel dunes a separate well defined function is proposed to describe the h l relationship for 2 d gravel dunes of maximum steepness there are few data on the hydrodynamic development of gravel dunes as a guide gravel dunes develop for a range of froude numbers up to 0 75 given that the nondimensional mean bed shear stress exceeds circa 0 1 dunes reach their maximum height at 0 25 and have reduced in height when 0 3 froude numbers of 0 84 and above lead to crestal flattening dune diminution and eventual replacement by antidunes or upper stage plane beds however owing to lag effects transitional bedforms have been recorded for froude numbers near the critical value of 1 the development of gravel dune steepness from lower stage plane bed through to upper stage plane bed is well described in only one case by dinehart 1992a fredsoe s 1975 function for equilibrium dune steepness applies reasonably well to dinehart s steepest dunes allen s 1984 bedform existence field based on and a characteristic grain size of the bed sediment has been extended from 5 mm to include bedstocks as coarse as 33 mm

application of 2d hydrodynamic modelling to high magnitude outburst floods an example from kverkfjoll iceland abstract high magnitude outburst floods cause rapid landscape change and are a hazard to life property and infrastructure however high magnitude fluvial processes and mechanisms of erosion transport and deposition are very poorly understood and remain largely unquantified this poor understanding is partly because of the inherent difficulty of directly measuring high magnitude outburst floods but also because of the limitations and assumptions of 1d models and other palaeohydrological methods which reconstructions of high magnitude floods have to date relied upon this study therefore applies a 2d hydrodynamic model sobek to reconstructing a high magnitude outburst flood this method offers the first calculations of high magnitude fluvial flow characteristics within an anastomosing network of simultaneously inundated channels including sheet or unconfined flow simultaneous channel and sheet flow flow around islands hydraulic jumps multi directional flow including backwater areas hydraulic ponding and multiple points of flood initiation 2d modelling of outburst floods clearly has the potential to revolutionise understanding of high magnitude spatial and temporal hydraulics and high magnitude flow phenomena geomorphological and sedimentological processes and hence rapid fluvial landscape change this potential for new understanding is because of the now wide availability of high resolution dem data for large and often inaccessible areas and the availability of remotely sensed data that can parameterise outburst flood sources such as glacial lakes for example additionally hydraulic models and computing power are now sufficient to cope with large 5 000 000 grid cells areas of inundation and large 100 000 m3 s 1 peak discharges

effects of upper ocean sound speed structure on deep acoustic shadow zone arrivals at 500 and 1000 km range deep acoustic shadow zone arrivals observed in the late 1990s in the north pacific ocean reveal significant acoustic energy penetrating the geometric shadow comparisons of acoustic data obtained from vertical line arrays deployed in conjunction with 250 hz acoustic sources at ranges of 500 and 1000 km from june to november 2004 in the north pacific with simulations incorporating scattering consistent with the garrett munk internal wave spectrum are able to describe both the energy contained in and vertical extent of deep shadow zone arrivals incoherent monthly averages of acoustic timefronts indicate that lower cusps associated with acoustic rays with shallow upper turning points utps where sound speed structure is most variable and seasonally dependent deepen from june to october as the summer thermocline develops surface reflected rays or those with near surface utps exhibit less scattering due to internal waves than in later months when the utp deepens data collected in november exhibit dra

airglow observations of nighttime medium scale traveling ionospheric disturbances from yonaguni statistical characteristics and low latitude limit the characteristics of nighttime medium scale traveling ionospheric disturbance mstid features observed over yonaguni 24 5 n 123 0 e 19 3 n dip latitude japan are studied using all sky imaging of oi 630 0 nm airglow emission the uniqueness of these observations is that the area observed by the imager covers the transition region between low to middle latitudes in the ionosphere typical low latitude limit of midlatitude type nighttime mstids possessing phase front alignments along the northwest to the southeast occurs in this region these mstid features are rarely sighted at dip latitudes below 15 we selected 2 year period for analysis in which 1 year corresponded to the solar minimum conditions and another year to the solar maximum conditions the mstids were observed to extend to farther lower latitudes during the solar minimum conditions than during the solar maximum periods their observed range of wavelengths phase velocities phase front alignment and propagation directions are similar to those observed at typical midlatitude sites however on many occasions the phase fronts of the observed mstids did not extend over the whole field of view of the imager indicating that some process inhibits their extension to further lower latitudes detailed investigation suggests that the poleward propagating enhancement of airglow intensity probably associated with the midnight pressure bulge causes the mstid features to disappear when they reach lower latitudes later in the night when the mstids reach lower latitudes well before midnight they are found to be inhibited by the equatorial ionization anomaly crest region

sixteen year variation of horizontal phase velocity and propagation direction of mesospheric and thermospheric waves in airglow images at shigaraki japan we analyzed the horizontal phase velocity of gravity waves and medium scale traveling ionospheric disturbances mstids by using the three dimensional fast fourier transform method developed by matsuda et al 2014 for 557 7 nm altitude 90 100 km and 630 0 nm altitude 200 300 km airglow images obtained at shigaraki mu observatory 34 8 n 136 1 e dip angle 49 over 16 years from 16 march 1999 to 20 february 2015 the analysis of 557 7 nm airglow images shows clear seasonal variation of the propagation direction of gravity waves in the mesopause region in spring summer fall and winter the peak directions are northeastward northeastward northwestward and southwestward respectively the difference in east west propagation direction between summer and winter is probably caused by the wind filtering effect due to the zonal mesospheric jet comparison with tropospheric re analysis data shows the difference in north south propagation direction between summer and winter is caused by differences in the latitudinal location of wave sources due to convective activity in the troposphere relative to shigaraki the analysis of 630 0 nm airglow images shows that the propagation direction of mstids is mainly southwestward with a minor northeastward component throughout the 16 years a clear negative correlation is seen between the yearly power spectral density of mstids and f10 7 solar flux this negative correlation with solar activity may be explained by the linear growth rate of the perkins instability and secondary wave generation of gravity waves in the thermosphere

glacier dammed lakes and geological work of glacial superfloods in the late pleistocene southern siberia altai mountains quaternary glacier dammed lakes ofsouthern siberia produced cataclysmic superfloods floodstreams at the initial and final glacial stages when the ice dams were unstable consequently the initial surface was greatly and geologically instantly transformed morphologic associations ofmountainous scablands developed similar to the diluvial complexes ofthe channeled scabland in north america giant diluvial ramparts and terraces bars diluvial berms and giant current ripple relief diluvial erosional and evorsional forms including spillways outburst and oversplash gorges and dry waterfalls are also present the discharges of the glacial superfloods which have been calculated by independent methods were hundreds ofcubic meters per second at the locations where the giant current ripple marks were formed up to millions of cubic meters per second within the gorges maximum discharges of18 10 6 m 3 s 1 were characteristic ofthe diluvial floods in the runoff channel f rom the chuya kuray system ofthe glacierdammed lakes below the mouth ofthe kuray depression as f as the settlement ofchibit the power ofthose floods reached 10 6 wm 2 these values exceed the hydraulic parameters ofthe jok ulhlaups from late quaternary lake missoula in north america the floods of which previously were considered the most powerful freshwater streams in earth history the last phenomenal glacial superflood with discharges in excess of1 10 6 m 3 s 1 occurred in the chuya and katun valleys no later than 13 000 years ago afterwards the glacier dammed lakes degraded simultaneously with the degradation of the glaciers the glacier dammed lakes ofthe intermontane basins in southern siberia disappeared completely at some time af ter 5000 years ago calculations ofthe hydraulics and the estimates ofthe geological activity ofthe quaternary jok ulhlaups mean that the diluvial processes of relief formation can now be viewed as the most powerful exogenous process r 2001 published by elsevier science ltd

paleoflood hydrology and extraordinary flood events paleoflood hydrology is the study of past or ancient flood events the most accurate technique involves the analysis of slackwater deposits and paleostage indicators swd psi slackwater deposits are sand and silt emplaced from suspension in exceptionally deep high velocity floods that characterize narrow deep canyons in resistant geologic materials these and other paleostage indicators are used to establish hydraulic grade lines for the generating flow events favorable sites for slackwater deposition include channel margin areas where stresses and velocities are reduced below critical values necessary to maintain fine grained bedload material sand and silt in suspension computerized procedures for hydraulic flow modeling are used to tie the elevations of the highest slackwater deposits to surveyed river cross sections the flood discharges calculated by this method can be calibrated through the study of modern floods on gaged rivers correlation of multiple swd psi sites along a river reach is used to identify the maximum paleostage achieved by a given flood advances in the dating of flood deposits permit estimates of flood frequency to be made extending over a data base of thousands of years the major geochronologic tool is radiocarbon dating of various kinds of organic matter intercalated with the slackwater deposits an important development is the use of the tandem accelerator mass spectrometer for direct measurement of 14c tiny blebs of charcoal seeds and other organics can be analyzed in order to date ancient flood deposits of hydrologic significance since swd psi studies yield very accurate determinations of paleoflood ages and magnitudes there is a pressing need for new statistical procedures that make optimum use of the information content in paleoflood records for flood frequency analysis nevertheless swd psi paleoflood hydrology has moved beyond the research phase its use should be encouraged in evaluating past experience of extraordinary floods at appropriate hazardous sites

constraining the timing of the most recent cataclysmic flood event from ice dammed lakes in the russian altai mountains siberia using cosmogenic in situ 10be ice dammed lakes were repeatedly formed in intermontane basins in the russian altai mountains throughout the pleistocene these cataclysmic outburst floods caused by ice dam failures were documented as earth9s largest flood waves by other geoscientists using in situ 10 be we successfully dated surfaces of flood associated boulders located in a former lake basin and downvalley from a former ice dam our precise surface exposure ages suggest that all boulders were associated with the most recent out of a number of cataclysmic floods that occurred at 15 8 1 8 ka the field location of the boulders implies that they were deposited by the largest late pleistocene flood that drained the chuya katun lake completely following initial dam failure a published reconstruction of the late glacial paleoenvironment in the vicinity of the former ice dam indicates that dam failure was likely a result of climatically induced downwasting of glaciers the failure of the ice dam provides more evidence for the timing of widespread warming during the late glacial in southern russia this flooding event in the headwaters of the ob river coincides with a freshwater peak as recorded in isotopic records of the kara sea and the arctic ocean

paleohydrology of late pleistocene superflooding altay mountains siberia cataclysmic flooding is a geomorphological process of planetary significance landforms of flood origin resulted from late pleistocene ice dammed lake failures in the altay mountains of south central siberia peak paleoflows which exceeded 18 x 10 6 cubic meters per second are comparable to the largest known terrestrial discharges of freshwater and show a hydrological scaling relation to floods generated by catastrophic dam failures these seem to have been earth9s greatest floods based on a variety of reconstructed paleohydraulic parameters

ground penetrating radar stratigraphy and dynamics of megaflood gravel dunes ground penetrating radar was used to elucidate the stratigraphy of late pleistocene gravel dunes in the altai mountains of southern siberia that formed when a lake emptied as a result of ice dam failure survey lines across dunes had a resolution of decimetres with depth penetration of 20 m the reflections identify bounding surfaces and radar facies two classes of unconformities are identified 1 an erosional unconformity at the base of the dunes 2 steeply inclined unconformities that truncate underlying inclined reflections and are downlapped by overlying inclined reflections within the dunes unconformities define six radar facies rf rf 1 basal subhorizontal discordant reflections rf 2 poorly defined discordant reflections rf 3 planar inclined reflections rf 4 sigmoidal inclined reflections rf 5 trough fills rf 6 low angle inclined reflections the basal unconformity represents the flood cut surface across which the dunes migrated the inclined unconformities may be interpreted in two ways 1 erosional surfaces induced by unsteady flow within one flood or 2 erosional surfaces developed by a series of floods reactivating dunes left stranded by previous floods the evidence favours the latter model which is consistent with the occurrence of several dune forming events within the basin the broader implications of the study are considered with respect to investigations of megaflood bedforms worldwide

last ice dammed lake in the kuray basin russian altai new results from multidisciplinary research abstract results from geomorphological sedimentological and geochronological analyses together with micropaleontological and mineralogical characteristics of lacustrine deposits in five locations within the kuray intermountain depression southeast altai mountains of south siberia support the thesis of repeated formations of ice dammed lakes during mis 2 and their draining by high energy floods our data suggest that the timing of one of the last cataclysmic draining events in the area can be estimated by an optically stimulated luminescence osl age of 19 0 1 1 ka for a sandy layer at the top of the diluvial i e large flood deposit revealed in a sedimentary sequence of the 1570 m a s l strandline one of the lowest preserved strandlines in the western part of the basin new osl and radiocarbon ages augmenting previously published dates indicate that the last lake to occupy the kuray depression occurred around 19 16 ka with a depth of at least 170 m in the central part of the basin and to a depth of no less than 220 m near the glacier dam lacustrine deposits are represented by two horizons of sandy clays separated by interlayers of mixed size sands the mineralogical data supported by analysis of sedimentological and micropaleontological records indicate accumulation of a lower lacustrine horizon in a deeper reservoir finding of leucocythere sp 1 leucocythere sp 2 and leucocythere dorsotuberosa ostracod species in lacustrine deposits characterizes these reservoirs as periglacial freshwater cold and deep lakes the presence of well crystallized mica and chlorite in lacustrine silts and clays from the lower lacustrine horizon indicates cold dry conditions at the time of their formation as well as a predominance of physical weathering of rocks within the denudation area after an abrupt dropping of the lake level around 16 ka determined from osl dating the lake never recovered its former depth the available radiocarbon ages for organic material in subaerial deposits within the study area and the new osl ages suggest that the last ice dammed lake in the kuray basin was drained between 16 7 and 9 9 ka the presence of this lake might explain the absence of late paleolithic surface finds within the basin that remained generally unsuitable for human habitation until its final drying the last outburst flood passed along the chuya and katun river valleys which had been already carved by older cataclysmic floods but did not significantly affect the topography downstream of the kuray chuya intermountain depressions we numerically simulated the draining of a palaeolake in the kuray basin with the water level 1650 m a s l maximal depth about 220 m near the dam with different scenarios of breaching the ice dam in contrast to a relatively gradual breach of the ice dam due to thermal erosion an instantaneous dam break due to structural failure can cause an outburst flood with a peak discharge of around 2 106 m3 s 1 the high speeds of the water flow 1 9 5 6 m s 1 with the maximum froude numbers of 0 06 0 22 and peak shields values of 0 03 0 25 indicate competence to mobilize gravel generally the simulated flow remained subcritical suggesting that bedforms developed under supercritical flows such as antidunes could not have developed although the development of dunes cannot be precluded our data also contribute to the issue of correlating the low lake strandlines in the kuray basin with the landforms associated with cataclysmic outburst floods

altai megafloods the temporal context abstract pleistocene floods from ice dammed lakes in the russian altai mountains are among the largest freshwater megafloods in earth history improved dating techniques have led to new dates constraining the timing of flood erosional and depositional events in addition to a variety of interpretations and explanations of event histories a proliferation of dates may increase confusion with respect to the characteristics and chronology of the flood events in a succinct review the main ice dammed lakes features the outburst floods and their repeated formation are presented among other indicators interbedded units of lacustrine deposits and outburst flood sediments in inya river valley demonstrate conclusively that there was a series of outburst floods with significant evidence for at least three high magnitude flood events prior study focussed on the interpretation of lake sediments shorelines giant bars gravel dunes dated by radiocarbon luminescence and cosmogenic nuclide assay the literature presents sometimes contradictory findings with respect to flood chronology these different interpretations evidence and arguments are reviewed for plausibility and consistency this consideration includes methodical and technical dating problems limited bleaching for luminescence techniques low purity for cosmogenic nuclide dating contamination of samples dated by radiocarbon assay at the current stage of knowledge the main period of repeated high magnitude outburst floods occurred between 28 ka and 15 ka bp indicators of earlier events are less distinct possible younger smaller floods can be identified after 15 ka bp but it is difficult to relate these to catastrophic lake draining rather they may relate to non catastrophic draining of residual small lakes within the larger basins the termination of the lake period took place before 9 9 0 3 ka cal bp in the kuray basin and in the chuya basin before 8 2 0 2 ka cal bp indicators are lacking for any drainage events after 7 7 0 6 ka as indicated by osl ages of aeolian deposits at low elevations in the katun valley relating the outburst floods to the temporal and spatial dynamics of the impounding glacier is challenging as with regard to pleistocene glaciation several conceptual models have been established supported by field evidence that in part can be contradictory during the period of the high magnitude outburst floods the extension thickness of the impounding valley glaciers were sufficient to form deep glacial lakes around the time of the last glacial maximum lgm yet the timing of the lgm remains controversial transferring glacial chronologies from mountain areas adjacent to the russian altai mountains to the environment of the megafloods does not provide a clearer picture as there is evidence for maximum stages at mis 4 and mis 3 in addition to recent postulations of a lgm in mis 2 for the russian altai mountains the russian altai mountains are located in a climatic transitional zone across which different lgm stages could be developed due to different moisture availability and temperature chronologies the effects of spatially variable rain shadows influencing the supply of moisture from the regional prevailing winds and local moisture sources from expanded ice dammed lakes complicates the picture and require further investigations

characteristics of nighttime medium scale traveling ionospheric disturbances observed over alaska 1 we focused on propagating wave like structures which frequently appeared in the o i 630 0 nm airglow images obtained by an all sky imager installed at poker flat research range 65 1 n 147 4 w magnetic latitude 65 6 in alaska these events are classified as medium scale traveling ionospheric disturbances mstids on the basis of the wavelength and propagating speed the unique points of our observation are 1 the two dimensional structures of mstids in the subauroral region are revealed 2 the horizontal direction of the electric field can be estimated from the motion of the evening co rotating patch ecp aurora appearing simultaneously and 3 neutral winds are simultaneously observed by a fabry perot spectrometer statistical study of these mstid events from november 2001 to april 2002 indicates the following characteristics the mstids were observed almost every evening and sometimes in the morning but were not observed at midnight typical propagating speed direction and wavelength of the wave phenomena were about 135 m s southwestward and about 250 km respectively when the mstids appeared northward neutral winds and westward plasma drifts were dominant this indicates that the perkins instability does not contribute to the development of mstids in the alaska region the vertical wavelength analysis using the dispersion relation of gravity waves with the observed wave parameters and background winds suggests that the observed mstids over alaska are the atmospheric gravity waves agws as a case study temporal variation of an mstid event on 21 december 2001 is shown results of a ray tracing analysis of this event suggest that the agws come from the equatorward edge of the auroral oval

sound speed fluctuations in the philippine sea observations from microcat sensors deployed as part of the 2004 spicex experiment indicate that the garrett munk internal wave energy spectrum at full strength appropriately describes the rms sound speed fluctuations in the north pacific in the region of the experimental deployment parabolic equation simulations incorporating sound speed field perturbations consistent with this model show remarkable agreement with acoustic data both in intensity and travel time spread the philippine sea is dynamically a very different region in the recent philsea09 deployment a single acoustic source mooring and an acoustic receiver mooring were outfitted with microcat sensors the hydrophone modules on the receiving array also housed calibrated thermistors the fluctuations of these measurements will be compared with the garrett munk spectrum to determine whether this model is accurate in this region of the philippine sea acoustic propagation models incorporating the observed fluctuations will be compared with acous

revisiting the dynamics of catastrophic late pleistocene glacial lake drainage altai mountains central asia abstract in this work we present a whole system model of megafloods from catastrophic ice dam failure in the late pleistocene that comprises the study of the dynamics of the glacial lake the propagation of the flood wave downstream of the dam and an approximation to the ice breach process the ice dam incision rate was simply considered an unknown constant which was varied systematically to best fit the maximum altitude of the simulated water surface and the paleostage indicators in the downstream valley during the transient megaflood hence the hydrograph resulting from the breach of the ice dam was not prescribed but was an output of the paleohydraulic reconstruction by considering two possible configurations of the breach in the ice dam i e full or partial removal of the ice we constrained the incision rate in the narrow range of 28 42 m h 1 two connected glacial lakes kuray and chuja released 95 of the stored water volume i e 564 km3 in 33 8 hours a peak discharge of 10 5 m m3 s 1 was required to form numerous giant bars and run up deposits in the chuja and katun valleys the peak streamflow occurred after 11 h when 45 of the available lake volume had been evacuated from the kuray and chuja basins further verification of the reconstructed megaflood was achieved by studying the computed hydraulic conditions during the lake draining that justify the existence and orientation of several fields of subaqueous gravel dunes in the glacial lake complex spatiotemporal patterns during the recession stage of the flood built most of the fields of bedforms in terms of nondimensional parameters the froude and shields numbers that formed the dune fields were similar to those observed in large sandy rivers but the flow was undoubtedly unsteady and two dimensional we conclude by noting that the extensions of the simulated area cannot be cropped or analysed by independent parts in order to predict the formation of the most relevant geological records due to the unsteady two dimensional nature of the flow motion and the development of backwater effects in the drainage network lastly the paleohydrological reconstruction of a megaflood has helped not only to infer the dynamics of the event but also to retrodict the mean parameters of the ice dam failure mechanism

traveling ionosphere disturbance signatures on ground based observations of the o 1d nightglow inferred from 1 d modeling this paper reports our simulations of the volume emission rate ver of the o 1d redline nightglow perturbed by waves traveling across the thermosphere at around 250 km altitude waves perturb

computational fluid dynamics simulations of the late pleistocene lake bonneville flood abstract at approximately 18 0 ka pluvial lake bonneville reached its maximum level at its northeastern extent it was impounded by alluvium of the marsh creek fan which breached at some point north of red rock pass idaho leading to one of the largest floods on earth about 5320 km3 of water was discharged into the snake river drainage and ultimately into the columbia river we use a 0d model and a 2d non linear depth averaged hydrodynamic model to aid understanding of outflow dynamics specifically evaluating controls on the amount of water exiting the lake bonneville basin exerted by the red rock pass outlet lithology and geometry as well as those imposed by the internal lake geometry of the bonneville basin these models are based on field evidence of prominent lake levels hypsometry and terrain elevations corrected for post flood isostatic deformation of the lake basin as well as reconstructions of the topography at the outlet for both the initial and final stages of the flood internal flow dynamics in the northern lake bonneville basin during the flood were affected by the narrow passages separating the cache valley from the main body of lake bonneville this constriction imposed a water level drop of up to 2 7 m at the time of peak flow conditions and likely reduced the peak discharge at the lake outlet by about 6 the modeled peak outlet flow is 0 85 106 m3 s 1 energy balance calculations give an estimate for the erodibility coefficient for the alluvial marsh creek divide of 0 005 m y 1 pa 1 5 at least two orders of magnitude greater than for the underlying bedrock at the outlet computing quasi steady state water flows water elevations water currents and shear stresses as a function of the water level drop in the lake and for the sequential stages of erosion in the outlet gives estimates of the incision rates and an estimate of the outflow hydrograph during the bonneville flood about 18 days would have been required for the outflow to grow from 10 to 100 of its peak value at the time of peak flow about 10 of the lake volume would have already exited eroding about 1 km3 of alluvium from the outlet and the lake level would have dropped by about 10 6 m

hydraulic control on the development of megaflood runup deposits abstract runup deposits are veneers of alluvium that drape floodway valley side walls above the height of giant bars deposited during megafloods given sufficient sediment supply the highest giant bars deposited in re entrants along the flood margins tend to grow to close to the maximum time averaged water level of the flood however considerable fluctuations in the water level caused by sediment charged floodwaters surging over shorter time scales are responsible for the higher runup deposits here the theoretical calculations of the expected maximum runup heights are compared with surveyed heights of six runup deposits in the chuja valley altai siberia the limitations and strengths of the theoretical approach are identified and modified parameters proposed that can be used to provide partial explanation for the differences between theory and observation conceptually surging can be viewed as caused by four interrelated elements 1 propagation of undular weir flow 2 macroturbulence 3 flow separation and 4 standing reflection and interference waves the heights of the observed runup deposits primarily are related to the depth of the flood water above the bar tops and to a lesser extent the froude number but tend to lie below the maximum surge heights of the modelled flow changes in the effective geometry of the flow re entrant mediating flow patterns as water depth increases is likely the cause of mismatch between theory and observation runup deposits may also lie at lower elevations than predicted because of sediment supply considerations and the return flow of surges combing down deposits nonetheless the difference between observed and predicted runup heights is often only a few tens of metres such that for deep floods runup deposits potentially are useful palaeostage indicators the analysis also indicates that upper stage plane beds do not dominate bar tops rather bar top deposition was primarily to lower stage plane beds from dense suspensions

problems of 14c dating in fossil soils within tectonically active highlands of russian altai in the chronological context of the late pleistocene megafloods abstract a complicated tectonic and sedimentation history of the high mountainous south eastern part of russian altai predetermined the presence of sources of ancient organic matter in the region during the pleistocene these deposits were affected by various exogenous processes that leads to mixing of young and old carbon in a unique for each sample ratio and strongly affects the results of radiocarbon dating this paper presents the results of multidisciplinary investigations of pedosedimentary sequences and discusses 14c dating of heterochronous organic matter in paleosols of two locations within the chuya basin in the chronological context of the late pleistocene megafloods in the kamsug valley reasonable evidence of the oldest pleistocene paleosols in the se altai is described for the first time the mineral composition of sediments and the results of pollen analysis argue for a short distant redeposition of the paleogene neogene parental substrate later it was transformed by pleistocene pedogenesis cryogenic processes particularly solifluction redox fluctuations resulted in redistribution of fe and mn the analysis of available radiocarbon dates indicates that the contamination of the samples by extraneous carbon and the insufficient data about the features of organic matter of the studied soils don t allow to draw a definite conclusion about the time of the pleistocene pedogenesis in the region the presented osl age 37 0 3 1 ka gdtl 3424 predates pedogenesis in this location as well as the last ice dammed lake formation in the chuya basin and its further cataclysmic draining followed by the deposition of cross bedded gravels and pebbles in the neighbouring yamanterek valley radiocarbon dating result for paleosol returns erratic aged date due to the influx of ancient organic matter similarly this date cannot serve as the upper chronological limit of ice dammed lakes existence in the chuya depression the radiocarbon ages 9 7 11 3 ka cal bp of charcoals from the underlying lens of humus sands postdate the last ice dammed lake with the water level at least 1980 m a s l it was demonstrated that short distant redeposition of the paleogene neogene sediments in the region preserves their main mineralogical and paleontological features it gives an opportunity to recognise such redeposited sediments which contain geological carbon meanwhile the redeposition followed by pedogenesis introduces younger organic matter diagenesis of such originally different organic matter contributes the final pool of organic carbon and results in the formation of heterogenous and heterochronous organic matter this should be taken into account while 14c dating and interpreting the obtained results

morphology sedimentology and palaeohydraulic significance of large gravel dunes altai mountains siberia coarse gravel bedforms which resulted from pleistocene glacial outburst floods are identified as subaqueous dunes comparison of the morphology of these fossil structures with modern dunes shows that the form of two dimensional 2 d transverse dunes and 3 d cuspate and lunate dunes developed in coarse gravels is comparable with sand dune morphology within lesser scale geophysical flows the similarity of the steepest gravel dunes with equilibrium dunes in sand indicates that grain size is not a major factor in constraining primary duneform internal structure indicates that flow over 2 d dunes was relatively uniform but over 3 d bedforms flow was locally variable flow separation and complex streaming of flow occurred over the steepest 3 d dunes cross beds are thin and few approach the angle of repose consequently most dunes did not migrate primarily by avalanching but by stoss entrained gravel transported over the crests rolling down and depositing on the lee slopes the lee formed when flood power was waning some dunes were siightly planed down during falling stage because lee side cross beds tend to be steeper than the angle of the preserved lee slope however silt rich caps indicate that any height reduction was contemporary with the final deposition of foresets post flood modification has been negligible although the modern topography is subdued by loess deposits within the dune troughs lee side sediments are often finer than the stoss slope sediments which indicates

statistical study of nighttime medium scale traveling ionospheric disturbances using midlatitude airglow images 1 we have investigated statistical characteristics of the nighttime medium scale traveling ionospheric disturbances mstids observed in 630 nm airglow images at two stations rikubetsu 43 5 n 34 8 mlat and shigaraki 34 9 n 25 4 mlat in japan for 1998 2000 near the solar maximum period most of the observed mstids propagate southwestward in the images the typical wavelength velocity period and amplitude are 100 300 km 50 100 m s 0 5 1 5 h and 5 15 respectively seasonal variations in these parameters are not clear the occurrence rate has a major peak 50 60 in summer that appears 2 months earlier at lower latitudes and a minor peak in winter similar occurrence characteristics are obtained from midlatitude spread f signatures using multipoint ionosonde data in japan though the coincidence of the spread f and the mstids in airglow images is only 10 15

a consideration of the dune antidune transition in fine gravel hydraulic data defining the dune antidune transition in fine gravel are compared with potential flow theory and information is drawn from published experiments and field based studies attention is given to both transitional bedforms and the development of downstream migrating antidunes in the latter case most data pertain to sand beds and not to gravel empirical data provide some weak support for the theoretical notion that the transition occurs at progressively lower froude numbers at greater relative depths although a critical froude number of 0 84 may reasonably be applied for the beginning of the dune to antidune transformation lag effects and a possible depth limitation ensure that transitional bedforms may persist across a broad range of froude numbers from 0 5 to 1 8 this latter observation has great relevance for palaeohydraulic estimates derived from outcrop data whereas the application of theoretical bedform existence fields based upon potential flow theory to fine gravel was previously purely speculative the addition of experimental and field data to these plots provides a degree of confidence in applying stability theory to practical geological problems for the first time laboratory data pertaining to downstream migrating gravel antidunes are compared with theory these bedforms have been reported from certain experimental near critical flows above sand or gravel beds but have been observed infrequently in natural streams however there are no detailed studies from natural rivers and only a few contentious identifications from outcrops nevertheless the limited hydraulic data conform to theoretical expectations

the fascination of a shallow water theory for the formation of megaflood scale dunes and antidunes abstract exceptional megaflood scale bedforms on earth are commonly associated with the catastrophic draining of glacial lakes in the late pleistocene the widest studied events have been the missoula and altai floods with 300 700 m flow depth 1 20 m bedform height and 10 300 m wavelength nowadays the saint venant equations have succeeded at simulating the catastrophic glacial lake drainage process numerically but we still lack a depth averaged morphodynamic theory able to predict the growth of dunes and antidunes the disparity of spatial scales in megafloods prevents the use of non depth averaged rotational flow equations motivating the present shallow water theory for the formation of megaflood scale bedforms we adopt a non equilibrium sediment transport equation rooted in einstein s pioneering work here we prove that the bed instability triggers to form dunes and antidunes simply by lagging the entrainment term for sediment mass conservation or the bottom shear stress with respect to the depth averaged flow velocity we formalise this result using a linear stability theory that captures the existence regions of dune and antidune in addition to the roll wave instability furthermore in the spirit of kennedy annu rev fluid mech vol 1 1969 pp 147 168 we derive a closed form solution of growth rate and wave speed of the bedform the nondimensional groups controlling the linear instabilities are the froude number r the shields parameter sh and the grain roughness relative to flow depth d subsequently we simulate the drainage of the largest missoula flood numerically to explain the formation of giant antidunes in the camas prairie montana us during the late stage of the megaflood also considered are large fields of gravel dunes in the kuray chuja lake basin altai mountains siberia the simulated hydraulic conditions over bedforms in both basins yield values of the nondimensional parameters that lie in the theoretical region of dunes and antidunes according to the proposed theory and in situ measurements in sandy rivers and flume experiments