dating the quaternary progress in luminescence dating of sediments abstract luminescence dating comprises a collection of numerical age techniques that are among the most significant chronological tools currently used in quaternary research this paper briefly reviews the key historical developments in luminescence dating from its roots in thermoluminescence dating of heated minerals to the development of optical dating methods for sunlight exposed sediments we describe the principles and practicalities of the various techniques commonly used in luminescence dating including multiple aliquot single aliquot and single grain procedures and we discuss some of the latest approaches to recognising and minimising potential errors in age estimation e g by means of component analysis and dose distribution methods in optical dating the overview also introduces the other papers in this special issue of quaternary science reviews which address a selection of important issues in basic research technique development and application of luminescence dating to critical questions in the geological and archaeological sciences illustrated with examples from around the world and the last million years of earth history

outburst floods from glacial lake missoula abstract the pleistocene outburst floods from glacial lake missoula known as the spokane floods released as much as 2184 km3 of water and produced the greatest known floods of the geologic past a computer simulation model for these floods that is based on physical equations governing the enlargement by water flow of the tunnel penetrating the ice dam is described the predicted maximum flood discharge lies in the range 2 74 106 13 7 106 m3 sec 1 lending independent glaciological support to paleohydrologic estimates of maximum discharge

meltwater floods into the black and caspian seas during heinrich stadial 1 abstract deglaciation of the eurasian ice sheet dispensed vast amounts of meltwater laden with red brown clay into black and caspian sea s freshwater lakes between 16 350 and 15 400 calendar years bp the arriving sediment had a mineral composition and strontium neodymium isotope signatures 87sr 86sr and end consistent with the crystalline bedrock that lay beneath the ice sheet as opposed to sources from landscapes crossed by the rivers that carried meltwater to the lakes the magnitude and rapidity of the shifts of 87sr 86sr and 18o in shells of ostracods and mollusks an eight fold increase in sediment accumulation rate and a plunge of 1250 14c years in the radiocarbon reservoir age indicate a volume of meltwater sufficient to have replaced most or all of the pre existing lake water if the release of 25 000 km3 of water from the caspian into the black sea s new euxine lake was abrupt by judging the magnitude of erosion in the floor of the manych strait spillway this event qualifies as a megaflood deeply scoured furrows channel floor bars and swaths of mounds 5 20 km in length and 5 20 m in height are reminiscent of scabland landscapes the meltwater is coincident with heinrich stadial 1 when the alpine and eurasian ice sheets re advanced and temperatures of the black sea s lake surface remained cold sand grains within the red brown clay indicate they were transported by lake surface ice

the role of wind in sediment removal from potholes in semiarid environments abstract potholes or rock basins are depressions that have been carved out of bedrock while there has been speculation in the literature regarding the processes involved in the addition or removal of sediment in existing potholes the processes have not been systematically documented this study attempts to fill this knowledge gap through data collection on 50 potholes in the navajo sandstone located on the top of rock window mesa in chinle valley az for spatial analysis we obtained a high resolution digital elevation model and detailed orthophoto of the mesa these data allowed us to precisely measure many aspects of the potholes which we then compared to wind data we collected to draw conclusions on how pothole morphology catchment size and water retention capacity affect the sediment removal processes wind measurements were done on 11 potholes with a range of sizes representative of the 50 potholes on the mesa wind speed across the top of the mesa is almost always greater than wind speed in the pothole at any given moment and there is a robust linear relationship between the wind speed above the pothole and the wind speed in the pothole for all shapes and sizes of potholes tested in dry conditions the wind speed threshold for sand removal from the potholes is about 50 km h independent of pothole size we observed the formation of wind eddies in the potholes which formed vortices several meters in height and these eddies traveling upward with a helical motion removed the sand we conclude that wind is an effective agent for the removal of sediment from the potholes preventing their infill via the accumulation of sand debris brought in by the wind and spalled from the pothole sides

periodic jokulhlaups from pleistocene glacial lake missoula new evidence from varved sediment in northern idaho and washington newly examined exposures in northern idaho and washington show that catastrophic floods from glacial lake missoula during late wisconsin time were repeated brief jokulhlaups separated by decades of quiet glaciolacustrine and subaerial conditions glacial priest lake dammed in the priest river valley by a tongue of the purcell trench lobe of the cordilleran ice sheet generally accumulated varved mud the varved mud is sharply interrupted by 14 sand beds deposited by upvalley running currents the sand beds are texturally and structurally similar to slackwater sediment in valleys in southern washington that were backflooded by outbursts from glacial lake missoula beds of varved mud also accumulated in glacial lake spokane or columbia in latah creek valley and elsewhere in northeastern washington the mud beds were disrupted in places violently during emplacement of each of 16 or more thick flood gravel beds this history corroborates evidence from southern washington that only one graded bed is deposited per flood refuting a conventional idea that many beds accumulated per flood the total number of such floodlaid beds in stratigraphic succession near spokane is at least 28 the mud beds between most of the floodlaid beds in these valleys each consist of between 20 and 55 silt to clay varves lacustrine environments in northern idaho and washington therefore persisted for two to six decades between regularly recurring colossal floods from glacial lake missoula

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

isotopically depleted late pleistocene groundwater in columbia river basalt aquifers evidence for recharge of glacial lake missoula floodwaters 1 late pleistocene outburst flooding of ice dammed glacial lake missoula and possible discharge from the cordilleran ice sheet cis catastrophically altered the northwestern united states landscape yet little is known about potential infiltration of flood waters into the subsurface this study provides compelling evidence for the presence of late pleistocene cis related recharge waters in the columbia river basalt aquifers crbas in central washington crba groundwaters with corrected 14c ages from 15 7 and 33 3 k yrs bp during periods of flood events have anomalously low 18o values 18 9 to 17 6 compared to late pleistocene soil waters 16 1 to 13 4 and modern precipitation in the region average 15 9 consistent with cis related meltwater recharge these results have implications for our understanding of megaflood phenomena on earth and mars

numerical simulations of large scale cataclysmic floodwater a simple depth averaged model and an illustrative application a simple numerical simulation code is developed to quantitatively discuss the behaviors of past cataclysmic floods whose rigorous hydraulic descriptions would be too complex to be supported by typically available field data the code aims to keep the basic equations simple and the required computational costs low which allows greater exploration of parameter space examination of both the qualitative meaning of turbulent equations and the relative importance of terms in the shallow water equation have resulted in the adoption of the depth averaged diffusion wave approximation in two dimensions as well as manning s empirical equation for simplification on the other hand topography is included as a boundary condition since topography plays an important role in selecting flood routes the model provides important advantages over theoretical analyses or one dimensional simulations including 1 the reproduction of complicated water flow paths such as bifurcations and reconvergences 2 the reconstruction of hydrological relationships among the water paths and 3 the direct comparison among the calculated extent of the flood inundation including floodwater depths and geological and geomorphological observations preliminary reconstructions of the missoula floods demonstrate the advantages of this new approach the method of coupling field based flood information with two dimensional analysis of an entire flow path provides a basis for estimating the peak discharges and flow durations of cataclysmic megafloods on earth with direct bearing on the understanding of regional paleohydrological histories of mars

the lemniscate loop comparisons with the shapes of streamlined landforms the lemniscate loop is a streamlined geometric form which has a simple algebraic equation containing a parameter whose value governs its overall length to width dimensions the lemniscate has been employed in geomorphology including comparisons with glacial drumlins and erosional streamlined islands in the channeled scabland of eastern washington and within the channels on mars these past comparisons have mainly been visual the present study involves more detailed quantitative comparisons between the lemniscate loop symmetrical airfoils drumlins and various islands formed by water flows the analyses focus primarily on the length to width ratios of these landscape features and their consistency with the analytical lemniscate shape many drumlins are found to be similar to the streamlined lemniscate but an equal number are more closely approximated by an elliptical geometric form the streamlined islands in rivers in the channeled scabland and in the martian channels all have nearly the same ave

middle late pleistocene landscape evolution of the dover strait inferred from buried and submerged erosional landforms abstract prominent landforms either buried or preserved at the seafloor provide important constraints on the processes that led to the opening and present day configuration of the dover strait here we extend previous investigations on two distinct landform features the fosse dangeard and lobourg channel to better understand the poly phase history of their formation and inferences for the opening and pleistocene evolution of the dover strait the fosse dangeard consist of several interconnected palaeo depressions their morphology and spatial distribution are interpreted to be the result of plunge pool erosion generated at the base of north eastward retreating waterfalls their infills comprise internal erosional surfaces that provide evidence for the occurrence of several erosional episodes following their initial incision the lobourg channel comprises various sets of erosional features attesting to the occurrence of several phases of intense fluvial and or flood erosion the last one of these carved a prominent inner channel which truncates the uppermost infill of the fosse dangeard the morphology of the lobourg inner channel and the erosional features associated with its incision strongly resemble landforms found in megaflood eroded terrains indicating that this valley was likely eroded by one or several megafloods our study therefore corroborates the existence of waterfalls in the dover strait at least once during the pleistocene epoch it also provides evidence of the occurrence of multiple episodes of fluvial and flood erosion including megafloods finally this study allows us to establish a relative chronology of the erosional depositional episodes that resulted in the present day morphology of this region

the modern evolution of geomorphology binghamton and personal perspectives 1970 2019 and beyond abstract the annual binghamton geomorphology symposia bgs began in 1970 initiated by professors donald r coates and marie morisawa of the state university of new york at binghamton the 50 bgs meeting topics through 2019 can be organized into five general themes as follows 1 applications 2 methods 3 process and form 4 history philosophy and theory 5 systems my own geomorphological research can be divided among these themes though it has not always been in tune with any prevailing paradigm the experience of the bgs meetings suggests that the immediate future of geomorphology will follow current trends involving technological advances in such areas as geochronology geospatial analysis lidar mapping computer simulation and systems based predictive modeling for the longer term it may be that the research frontiers will lie in outer and inner space with the former involving the discovery and analysis of the surfaces of earth like planets within and beyond our own solar system the challenges of inner space may be even more profound as they are imposed against the background of rapidly accelerating advances in artificial intelligence

number and size of last glacial missoula floods in the columbia river valley between the pasco basin washington and portland oregon field evidence and radiocarbon age dating combined with hydraulic flow modeling provide new information on the magnitude frequency and chronology of late pleistocene missoula floods in the columbia river valley between the pasco basin washington and portland oregon more than 25 floods had discharges of 1 0 106 m3 s at least 15 floods had discharges of 3 0 106 m3 s at least six or seven had peak discharges of 6 5 106 m3 s and at least one flood had a peak discharge of 10 106 m3 s a value consistent with earlier results from near wallula gap but better defined because of the strong hydraulic controls imposed by critical flow at constrictions near crown and mitchell points in the columbia river gorge stratigraphy and geomorphic position combined with 25 radiocarbon ages and the widespread occurrence of the ca 13 ka radiocarbon years mount st helens set s tephra show that most if not all the missoula flood deposits exposed in the study area were emplaced after 19 ka radiocarbon years and many were emplaced after 15 ka more than 13 floods perhaps postdate ca 13 ka including at least two with discharges of 6 106 m3 s from discharge and stratigraphic relationships upstream we hypothesize that the largest flood in the study reach resulted from a missoula flood that predated blockage of the columbia river valley by the cordilleran ice sheet multiple later floods probably including the majority of floods recorded by fine and coarse grained deposits in the study area resulted from multiple releases of glacial lake missoula that spilled into a blocked and inundated columbia river valley upstream of the okanogan lobe and were shunted south across the channeled scabland

large scale cenozoic wind erosion in the puna plateau the salina del fraile depression wind erosion is integral to the evolution of arid landscapes on earth and mars but the nature of long term wind erosion of bedrock is poorly understood here we describe the salina del fraile sdf

landscape formation at the deuteronilus contact in southern isidis planitia mars implications for an isidis sea abstract two of the most widely studied landforms that are associated with a putative ocean that filled the northern hemisphere of mars are 1 the vastitas borealis formation vbf plain units that cover a larger portion of the northern lowlands of mars and 2 a candidate paleoshoreline e g the deuteronilus contact which represents the outer margin of the vbf the vbf and the deuteronilus contact are interpreted to result from a short lived late hesperian ocean that readily froze and sublimated similar landforms are also present in the impact basin of isidis planitia and suggest formation processes comparable to those that formed the vbf and the deuteronilus contact in the northern lowlands our study of the deuteronilus contact in isidis revealed geologic evidence that possibly supports the existence of a late hesperian early amazonian isidis sea for example numerous valleys that are incised into the plains of the southern isidis basin rim between 82 90 e and 3 6 n and trend a few tens of kilometers to the north following the general topographic gradient toward the center of isidis planitia a few of them reach the deuteronilus contact and continue as sinuous ridges in the isidis interior plains iip based on our findings we conclude that the geologic setting along the deuteronilus contact including the valleys and ridges is a result of 1 late hesperian short term fluvial activity 2 a late hesperian early amazonian short lived isidis sea that readily froze 3 subglacial drainage and esker formation and 4 subsequent sublimation of the proposed isidis ice sheet although the fluvio glacial model we introduce in our manuscript cannot fully explain the geologic setting possible alternative formation models including relief inversion and fluvio volcanic scenarios are even less capable in explaining the observed geologic setting along the deuteronilus contact

stratigraphic evidence for multiple drainings of glacial lake missoula along the clark fork river montana usa abstract glacial lake missoula a source of channeled scabland flood waters inundated valleys of northwest montana to altitudes of 1265 m and to depths of 600 m as evidenced by shorelines and silty lacustrine deposits this study describes previously unrecognized catastrophic lake drainage deposits that lie stratigraphically beneath the glacial lake silts the unconsolidated gravelly flood alluvium contains imbricated boulder sized clasts cross stratified gravel with slip face heights of 2 35 m and 70 to 100 m high gravel bars which all indicate a high energy high volume alluvial environment gravel bars and high scablands were formed by catastrophic draining of one or possibly more early high lake stands 1200 1265 m most glacial lake silt such as the ninemile section was deposited stratigraphically above the earlier deposits represents a lower lake stand s 1050 1150 m and was not deposited in lake s responsible for the highest discharge events the glaciolacustrine silt covered benches are incised by relict networks of valleys formed during the drainage of the last glacial lake significant erosion associated with the last lake draining was confined to the inner clark fork river canyon

a lake in uzboi vallis and implications for late noachian early hesperian climate on mars abstract uzboi vallis centered at 28 s 323 e is 400 km long and comprises the southernmost segment of the northward draining uzboi ladon morava ulm meso scale outflow system that emerges from argyre basin bond and holden craters blocked the valley to the south and north respectively forming a late noachian to hesperian paleolake basin that exceeded 4000 km 3 limited crism data suggest lake deposits in uzboi and underlying basin floor incorporate relatively more mg clays and more fe clays respectively the short lived lake overflowed and breached holden crater s rim at an elevation of 350 m and rapidly drained into the crater fan deltas in holden extend 25 km from the breach and incorporate meter sized blocks and longitudinal grooves along the uzboi basin floor are hundreds of meters long and average 60 m wide suggesting high discharge drainage of the lake precipitation derived runoff rather than regional groundwater or overflow from argyre dominated contributions to the uzboi lake although the failure of most tributaries to respond to a lowering of base level indicates their incision largely ended when the lake drained the uzboi lake may have coincided with alluvial and or lacustrine activity in holden eberswalde and other craters in southern margaritifer terra where fluvial lacustrine activity may have required widespread synoptic precipitation rain or snow perhaps associated with an ephemeral global hydrologic system during the late noachian into the hesperian on mars

the channeled scabland back to bretz the channeled scabland washington state united states is only partly the result of erosion by the catastrophic drainage of glacial lake missoula there were other sources of meltwater recent sedimentary investigations of some sites in the missoula basin and in the channeled scabland support a single large late wisconsin flood as opposed to multiple floods proposed for this time period sediment in the glacial lake missoula basin records rapid infill by jokulhlaups draining into lake missoula from upstream punctuating a long period of normal varve sedimentation this was independent of sedimentation in the main scabland tract where proximal and distal rhythmic beds are explained as resulting from multiple pulses or surges within a single flood geomorphic and sedimentary evidence supports the conclusion that drainage from the cordilleran trunk valleys was important and pulses were probably related to the drainage of these valleys

river incision into bedrock mechanics and relative efficacy of plucking abrasion and cavitation improved formulation of bedrock erosion laws requires knowledge of the actual processes operative at the bed we present qualitative field evidence from a wide range of settings that the relative efficacy of the various processes of fluvial erosion e g plucking abrasion cavitation solution is a strong function of substrate lithology and that joint spacing fractures and bedding planes exert the most direct control the relative importance of the various processes and the nature of the interplay between them are inferred from detailed observations of the morphology of erosional forms on channel bed and banks and their spatial distributions we find that plucking dominates wherever rocks are well jointed on a submeter scale hydraulic wedging of small clasts into cracks bashing and abrasion by bedload and chemical and physical weathering all contribute to the loosening and removal of joint blocks in more massive rocks abrasion by suspended sand appears to be rate limiting in the systems studied here concentration of erosion on downstream sides of obstacles and tight coupling between fluid flow patterns and fine scale morphology of erosion forms testify to the importance of abrasion by suspended load rather than bedload particles mechanical analyses indicate that erosion by suspended load abrasion is considerably more nonlinear in shear stress than erosion by plucking in addition a new analysis indicates that cavitation is more likely to occur in natural systems than previously argued cavitation must be considered a viable process in many actively incising bedrock channels and may contribute to the fluting and potholing of massive unjointed rocks that is otherwise attributed to suspended load abrasion direct field evidence of cavitation erosion is however lacking in terms of the well known shear stress or stream power erosion law erosion by plucking is consistent with a slope exponent n of 2 3 to 1 whereas erosion by suspended load abrasion is more consistent with a slope exponent of 5 3 given that substrate lithology appears to dictate the dominant erosion process this finding has important implications for long term landscape evolution and the models used to study it

tephrochronologic constraints on the late pleistocene history of the southern margin of the cordilleran ice sheet western washington abstract an ash layer that appears geochemically correlative with mt st helens tephra set s occurs in a sequence of pleistocene lake sediments in the ohop valley of the southern puget lowland below vashon till deposited during the maximum late pleistocene advance fraser glaciation of the puget lobe of the cordilleran ice sheet the puget lobe reached its maximum southern extent ca 14 000 14 500 yr b p and at least part of set s is evidently somewhat older previous radiocarbon and thermoluminescence dates for set s have ranged from 13 000 to 16 000 yr b p geochemically correlative deposits of set s tephra occur in slackwater sediments coeval with the missoula floods in eastern washington produced by jokulhlaups through the purcell trench lobe of the cordilleran ice sheet these relationships suggest that advances of glacier lobes on the southern margin of the cordilleran ice sheet were nonsynchronous as the pucell trench lobe east of the cascade range advanced to its maximum southern extent prior to the time of the eruption of set s before the puget lobe west of the cascades reached its maximum southern extent

identification of a kulshan caldera correlative tephra in the palouse loess of washington state northwest usa abstract the kulshan caldera formed at 1 15 ma on the present day site of mt baker washington state northwest usa and erupted a compositionally zoned dacite rhyolite magma and a correlative eruptive the lake tapps tephra this tephra has previously been described but only from the puget lowland of nw washington here an occurrence of a kulshan caldera correlative tephra is described from the quaternary palouse loess at the washtucna site wa 3 site wa 3 is located in east central washington 340 km southeast of the kulshan caldera and 300 km east southeast of the lake tapps occurrence in the puget lowland major and trace element chemistry and location of the deposit at washtucna within reversed polarity sediments indicates that it is not correlative with the mesa falls rockland bishop ash lava creek b or huckleberry ridge tephras instead the washtucna deposit is related to the lake tapps tephra by fractional crystallisation but is chemically distinct a consequence of its eruption from a compositionally zoned magma chamber the correlation of the washtucna occurrence to the kulshan caldera forming eruption indicates that it had an eruptive volume exceeding 100 km3 and that its tephra could provide a valuable early pleistocene chronostratigraphic marker in the pacific northwest

paleoflood hydrology origin progress prospects from an origin in diverse studies of flood geomorphology and quaternary geology paleoflood hydrology emerged as a geophysical and an applied hydrological science during the 1970s and 1980s since acquiring its formal name in 1982 the most productive approach in paleoflood hydrology has become energy based inverse hydraulic modeling of discrete paleoflood events recorded in appropriate settings as slackwater deposits and other paleostage indicators swd psi or as various threshold indicators of non exceedence technological advances particularly in hydraulic modeling and geochronology were instrumental in moving the discipline to its present status the most recent advances include 1 new techniques for the accurate geochronology of flood sediments notably tams radiocarbon analyses and osl dating and 2 the phenomenal increase in computer power that allows complex hydraulic calculations to become feasible for routine studies from its initial demonstration in the southwestern united states swd psi paleoflood hydrology proved its widespread applicability to various landscape environments particularly important studies have been accomplished in australia china india israel south africa spain and thailand paleoflood hydrology has also generated its share of controversy in part because of the differing viewpoints and attitudes of the two scientific traditions from which it emerged quaternary geology geomorphology versus applied hydrologic hydraulic engineering nevertheless the future growth of the discipline is assured given the rapid pace of discoveries that it engenders indeed so many international studies exist that it is appropriate to pursue global syntheses to address interesting and timely questions of extreme flood phenomena in relation to global climatic change

magnetostratigraphic evidence from the cold creek bar for onset of ice age cataclysmic floods in eastern washington during the early pleistocene this study provides a detailed magnetostratigraphy of sediments composing the cold creek cataclysmic flood bar in the pasco basin washington our interpretation suggests onset of missoula floods or similar events prior to 1 1 myr later than previously suggested by bjornstad et al bjornstad b n fecht k r pluhar c j 2001 long history of pre wisconsin ice age cataclysmic floods evidence from southeastern washington state journal of geology 109 6 695 713 nonetheless these data suggest that channeled scabland features formed over a much longer timespan than commonly cited that continental ice sheets of the early pleistocene reached as far south as those of the late pleistocene and that similar physiography existed in eastern washington and perhaps montana to both generate and route missoula flood like events this study adds paleomagnetic polarity results from 213 new samples of silts and sands derived from nine new drill cores penetrating the cold creek cataclysmic flood bar to our previous database of 53 samples from four boreholes resulting in a much more robust and detailed magnetostratigraphy rock magnetic studies on these sediments show pure magnetite to be the predominant remanence carrying magnetic mineral ruling out widespread remagnetization by secondary mineralization the magnetostratigraphy at eastern cold creek bar is characterized by a normal polarity interval bracketed by reversed polarities equating the normal zone with the jaramillo subchron 0 99 1 07 myr affords the simplest correlation to the magnetic polarity timescale western cold creek bar was likely deposited during the brunhes chron 0 0 78 myr since it exhibits mainly normal polarities with only two thin reversed polarity horizons that we interpret as magnetic excursions during the brunhes

case for periodic colossal jokulhlaups from pleistocene glacial lake missoula two classes of field evidence firmly establish that late wisconsin glacial lake missoula drained periodically as scores of colossal jokulhlaups glacier outburst floods 1 more than 40 successive flood laid sand to silt graded rhythmites accumulated in back flooded valleys in southern washington hiatuses are indicated between flood laid rhythmites by loess and volcanic ash beds disconformities and nonflood sediment between rhythmites are generally scant because precipitation was modest slopes gentle and time between floods short 2 in several newly analyzed deposits of pleistocene glacial lakes in northern idaho and washington lake beds comprising 20 to 55 varves average 30 40 overlie each successive bed of missoula flood sediment these and many other lines of evidence are hostile to the notion that any two successive major rhythmites were deposited by one flood they dispel the notion that the prodigious floods numbered only a few the only outlet of the 2 500 km 3 glacial lake missoula was through its great ice dam and so the dam became incipiently buoyant before the lake could rise enough to spill over or around it like grimsvotn iceland lake missoula remained sealed as long as any segment of the glacial dam remained grounded when the lake rose to a critical level 600 m in depth the glacier bed at the seal became buoyant initiating underflow from the lake subglacial tunnels then grew exponentially leading to catastrophic discharge calculations of the water budget for the lake basin including input from the cordilleran ice sheet suggest that the lakes filled every three to seven decades the hydrostatic prerequisites for a jokulhlaup were thus re established scores of times during the 2 000 to 2 500 yr episode of last glacial damming j harlen bretz9s spokane flood outraged geologists six decades ago partly because it seemed to flaunt catastrophism the concept that lake missoula discharged regularly as jokulhlaups now accords bretz9s catastrophe with uniformitarian principles

magnitudes and implications of peak discharges from glacial lake missoula new field evidence and discharge calculation procedures provide new estimates of maximum late pleistocene glacial lake missoula flood discharges for two important reaches along the flood route within the spokane valley near the point of release the peak discharge probably exceeded 17 3 million m3 sec 1 downstream at wallula gap a major point of flow convergence peak discharge was about 10 2 5 million m3sec 1 flow duration was on the order of several days these are the largest known terrestrial fresh water flows consideration of these discharge values constrains models for the failure of glacial lake missoula the maximum discharges estimated here are larger than theoretical and empirical predictions of maximum subglacial jokulhlaup style releases for lake missoula we postulate consistent with geological relations in the glacial lake missoula basin and in the channeled scabland that the largest late wisconsinan missoula flood resulted from a cataclysmic failure of the impounding ice dam of glacial lake missoula this large release may have been the result of a complete rupture of the ice dam subsequent multiple flows of lesser magnitude may have resulted from repeated subglacial releases from the lake

sedimentary imprints of former ice sheet margins insights from an end ordovician archive sw libya fromthe proterozoic to the quaternary the evolution of the earthwas characterised by recurrent periods of glaciation however the margins of many ancient ice sheets are poorly defined on palaeogeographic reconstructions the extent and outlines of ancient ice sheets can be better understood through careful documentation of sediments deposited at the ice sheet margin an outstanding example is provided herein based on an end ordovician archive in libya tihemboka area murzuq basin the four sets of structures include i subglacial glaciotectonic structures and soft sediment deformations from flowing glacier ice such as intraformational glacial striae intraformational deformation shear planes sheath folds normal microfaults and large scale glaciotectonic folds and thrusts ii structures resulting from overpressured subglacial meltwater flows such as clastic dykes and tunnel valleys iii proglacial depositional structures and facies related to highmagnitude meltwater floods such as sandstone intraclasts large scale bedforms resulting from supercritical flows climbing dune cross stratification and kettle holes and iv deformation structures resulting from free floating and nonglacier ice such as ice keel scours and ice crystal marks such a set of structures points to an ice marginal essentially continental depositional setting and provides an excellent suite of criteria to identify margins of ancient ice sheets in the stratigraphic record at a regional scale a reconstruction through time and space of the related depositional wedge is proposed this corresponded to a seismic scale n120 m in thickness 40 km in length ice marginal wedge in front of an essentially warm based ice sheet inducing concomitant large scale glaciotectonic deformation glacial basin and tunnel valley downcuttings the related ice front was associated with high energy meltwater flows feeding a network of deeply incised proglacial channels downstream and beyond them a fluvioglacial deltaic system shallow ice marginal permafrost most likely affected the depositional wedge at a larger scale the tihemboka ice marginal wedge is interpreted as related to a stillstand period over the gondwana platform developed over an estimated interval of a few thousands of years based on these data the conditions that arose in a particularly favourable context for the development the preservation and the identification of ice marginal wedges in the geological record are reviewed significant meltwater derived sediment deposition and aggradation in an accommodation space resulting either from preglacial inheritance glacial downcuttings and or glacio isostatic lithospheric flexure or active tectonic subsidence 1 myr are required for their formation and subsequent preservation

emplacement of the youngest flood lava on mars a short turbulent story abstract recently acquired data from the high resolution imaging science experiment hirise context ctx imager and compact reconnaissance imaging spectrometer for mars crism onboard the mars reconnaissance orbiter mro spacecraft were used to investigate the emplacement of the youngest flood lava flow on mars careful mapping finds that the athabasca valles flood lava is the product of a single eruption and it covers 250 000 km 2 of western elysium planitia with an estimated 5000 7500 km 3 of mafic or ultramafic lava calculations utilizing topographic data enhanced with mro observations to refine the dimensions of the channel system show that this flood lava was emplaced turbulently over a period of only a few to several weeks this is the first well documented example of a turbulently emplaced flood lava anywhere in the solar system however mro data suggest that this same process may have operated in a number of martian channel systems the magnitude and dynamics of these lava floods are similar to the aqueous floods that are generally believed to have eroded the channels raising the intriguing possibility that mechanical erosion by lava could have played a role in their incision

the channeled scabland back to bretz comment and replycomment the major controversy regarding the origin of the channeled scabland is whether the landforms were formed mainly by multiple periodic floods or by a grand scale cataclysmic flood from late pleistocene glacial lake missoula evidence for the multiple flood as many as 40 as estimated by waitt 1980

missoula flood dynamics and magnitudes inferred from sedimentology of slack water deposits on the columbia plateau washington sedimentological study of late wisconsin missoula flood slack water sediments deposited along the columbia and tucannon rivers in southern washington reveals important aspects of flood dynamics most flood facies were deposited by energetic flood surges velocities 6 m sec entering protected areas along the flood tract or flowing up and then directly out of tributary valleys true still water facies are less voluminous and restricted to elevations below 230 m high flood stages attended the initial arrival of the flood wave and were not associated with subsequent hydraulic ponding upslope from channel constrictions among 186 flood beds studied in 12 sections 57 have bioturbated tops and about half of these bioturbated beds are separated from overlying flood beds by nonflood sediments a single graded flood bed was deposited at most sites during most floods sequences in which 2 9 graded beds were deposited during a single flood are restricted to low elevations these sequences imply complex multi peaked hydrographs in which the first flood surge was generally the largest and subsequent surges were attenuated by water already present in slack water areas slack water sediment stratigraphy suggests a wide range of flood discharges and volumes of 40 documented late wisconsin floods that inundated the pasco basin only about 20 crossed the palouse snake divide floods younger than the set s tephras from mount st helens were generally smaller than earlier floods of late wisconsin age although most still crossed the palouse snake divide these late floods primarily traversed the cheney palouse scabland because stratigraphy of slack water sediment along the columbia river implies that the largest flood volumes did not enter the pasco basin by way of the columbia river

record of pre late wisconsin giant floods in the channeled scabland interpreted from loess deposits loess deposits adjacent to flood coulees on the columbia plateau in eastern washington state record multiple episodes of pre late wisconsin cataclysmic floods evidence in the loess consists of flood cut unconformities upward fining in individual loess strata and flood deposits that consist of basaltic gravel fragments of calcified paleosols and slackwater sediment at least six episodes of floods during the pleistocene are indicated by paleomagnetic measurements tephra correlations and the stratigraphic position of flood indicators one episode of the six occurred prior to 790 ka the most recent episode before the last glacial floods occurred at 36 ka at the latest

the age and origin of the labyrinth western dry valleys antarctica evidence for extensive middle miocene subglacial floods and freshwater discharge to the southern ocean a 50 km long network of bedrock channels and scoured terrain occupies the ice free portion of a major trough that crosses the transantarctic mountains in southern victoria land the channels collectively termed the labyrinth emerge from beneath the margin of the east antarctic ice sheet wright upper glacier and are incised into a 300 m thick sill of ferrar dolerite at the head of wright valley upper and intermediate elevation erosion surfaces of the labyrinth exhibit striations and molding characteristic of glacial erosion channels and canyons on the lower surface are as much as 600 m wide and 250 m deep have longitudinal profiles with many reverse gradients and contain potholes 35 m deep at tributary junctions these characteristics are most consistent with incision from fast flowing subglacial meltwater estimated discharge is on the order of 1 6 2 2 10 6 m 3 s 1 our 40 ar 39 ar analyses of volcanic tephra from the labyrinth show that the chan nels are relict that major channel incision predates 12 4 ma and that the last major subglacial flood occurred sometime between 14 4 ma and 12 4 ma the most plausible origin for the labyrinth is erosion associated with episodic drainage of subglacial lakes in east antarctica one compelling possibility is that discharge of large volumes of sub glacial meltwater to the southern ocean and to the ross sea in particular may have coincided with and contributed to oscillations in regional and or global climate during the middle miocene

resolving spatial heterogeneities in exhumation and surface uplift in timor leste constraints on deformation processes in young orogens although exhumation and surface uplift are important parameters in understanding orogenesis the opportunity to measure both in close proximity is rare in timor leste east timor deeply exhumed metamorphic rocks and piggyback deepwater synorogenic basins are only tens of kilometers apart permitting direct relation of uplift and exhumation by comparing micropaleontology to thermochronology interpreted through one dimensional thermal modeling foraminifera in two deepwater synorogenic basins suggest basin uplift from depths of 1 2 km to depths of 350 1000 m between 3 35 and 1 88 ma thermochronologic sampling was conducted in the central mountain belt between these basins of four muscovite 40ar 39ar samples one provides a reset age of 7 13 0 25 ma in the aileu high grade belt that suggests 9 16 km of exhumation since that time eighteen zircon u th he samples contain a group of reset ages in the aileu complex ranging from 4 4 to 1 5 ma which suggest exhumation rates of 1 0 3 1 mm yr with 2 7 7 8 km of exhumation since these ages thirteen apatite u th he ages in the gondwana sequence range from 5 5 to 1 4 ma suggesting 1 2 km of exhumation and defining a pattern of exhumation rates ranging from 0 2 to 1 3 mm yr that positively correlates with average annual rainfall seven apatite fission track samples display varying degrees of partial resetting with greatest resetting where apatite u th he ages are youngest together these data demonstrate extreme variability in surface uplift and exhumation over small spatial scales we propose ongoing subsurface duplexing driven by subduction and underplating of australian continental crust as the predominant driver for surface uplift and uplift induced exhumation

rapid discharge connects antarctic subglacial lakes a hidden subglacial world consisting of more than 140 lakes lies beneath the antarctic ice sheet it is widely assumed that these lakes are a static ecosystem cut off from each other and the rest of the world far from it according to a 16 month study of surface elevation changes in the region changes indicating a rapid discharge of water from one lake to another were detected and it is possible that the entire subglacial drainage basin is flushed through periodically by massive water transfers observation of surface elevation changes over 16 months in an area of the east antarctic ice sheet overlying subglacial lakes suggests a rapid discharge of one lake to at least two other lakes involving a water volume of 1 8 km3 in conflict with previous expectations that subglacial lakes have long residence times and slow circulations the existence of many subglacial lakes1 provides clear evidence for the widespread presence of water beneath the east antarctic ice sheet but the hydrology beneath this ice mass is poorly understood2 such knowledge is critical to understanding ice flow basal water transfer to the ice margin glacial landform development and subglacial lake habitats here we present ice sheet surface elevation changes in central east antarctica that we interpret to represent rapid discharge from a subglacial lake our observations indicate that during a period of 16 months 1 8 km3 of water was transferred over 290 km to at least two other subglacial lakes while viscous deformation of the ice roof above may moderate discharge the intrinsic instability of such a system3 suggests that discharge events are a common mode of basal drainage4 if large lakes such as lake vostok or lake concordia1 are pressurizing it is possible that substantial discharges could reach the coast5 6 our observations conflict with expectations that subglacial lakes have long residence times and slow circulations2 7 8 and we suggest that entire subglacial drainage basins may be flushed periodically the rapid transfer of water between lakes would result in large scale solute and microbe relocation and drainage system contamination from in situ exploration is therefore a distinct risk

did the martian outflow channels mostly form during the amazonian period simud tiu and ares valles comprise some of the largest outflow channels on mars their excavation has been attributed variously to or a combination of erosion by catastrophic floods glaciers and debris flows numerous investigations indicate that they formed largely during the late hesperian 3 61 3 37 ga however these studies mostly equate the ages of the outflow channel floors to those of the flows that generated mesoscale several hundred meters to a few kilometers bedforms within them to improve the statistical accuracy in the age determinations of these flow events we have used recently acquired high resolution image and topographic data to map and date portions of simud tiu and ares valles which are extensively marked by these bedforms our results which remove the statistical effects of older and younger outflow channel floor surfaces on the generation of modeled ages reveal evidence for major outflow channel discharges occurring during the early 3 37 1 23 ga and middle 1 23 0 328 ga amazonian with activity significantly peaking during the middle amazonian stages we also find that during the documented stages of middle amazonian discharges the floor of tiu valles underwent widespread collapse resulting in chaotic terrain formation in addition we present evidence showing that following the outflow channel discharges collapse within northern simud valles generated another chaotic terrain this younger chaos region likely represents the latest stage of large scale outflow channel resurfacing within the study area our findings imply that in southern circum chryse the martian hydrosphere experienced large scale drainage during the amazonian which likely led to periodic inundation and sedimentation within the northern plains

photogeologic mapping and the geologic history of the hellas basin floor mars abstract the hellas basin on mars is the second largest topographically well defined impact structure in the solar system and has repeatedly been interpreted as a major sink of volcanic glacio fluvial and eolian materials based on established guidelines for planetary mapping we compiled a comprehensive photogeological map of hellas planitia i e the hellas basin floor 1 2 000 000 1 8 106 km2 see supplementary online material using the thermal emission imaging system themis ir day time mosaic as basemap supplemented by several other datasets we identified 33 units which were categorized into a rim assemblage containing dissected units a layered rim sequence and other basin rim units as well as a floor assemblage containing the honeycomb formation an interior formation and a plains sequence relative dating of units was performed wherever contacts revealed stratigraphic relationships and was complemented by absolute model ages amas of all units that lend themselves to reliable crater size frequency distribution csfds measurements on the basis of our results as well as amas of circum hellas volcanic provinces by previous authors we compiled a chronostratigraphic model of the hellas basin floor the northern basin rim shows evidence vast layered hydrous mineral bearing deposits containing meandering channel like valleys that the early history of the basin until 3 8 ga ago experienced extended periods of low energy fluvial and possibly lacustrine activity superposing the layered rim sequence the majority of the hellas basin infill 1 5 1 7 106 km3 consists of volcanic material a lower and an upper wrinkle ridged plains unit which was shortened by a compressive stress field relatively soon after its emplacement based on their ages and stratigraphic considerations we identified malea patera and possibly also tyrrhena patera as a suitable source for the older lower plains 3 8 ga and hadriaca and or amphitrites paterae for the younger upper plains 3 7 ga shortly after these volcanic episodes the entire basin floor was covered by large amounts of deposits 106 km3 containing aqueously altered mafic materials we interpret the deposits to have originated from hesperia planum and the hesperia hellas trough where they might have been removed by glacio fluvial processes which also sculpted the hellas rim sections along northern promethei terra and malea planum around the same time such an apparent correlation between nearby volcanic activity and increased erosion deposition is in agreement with previous models which suggest outgassing by a maximum in global volcanism at that time caused warmer episodes enabling repeated subaerial water run off after the emplacement of these deposits intense erosion likely deflation along a rim parallel annulus began to exhume the outer parts of the wrinkle ridged plains again forming an interior formation of more elevated erosional remnants including the alpheus colles since 3 7 ga ago fluvial activity of dao niger and harmakhis valles dissected the eastern plains and emplaced pancake shaped deposits in the basin center later deflation and abrasion by katabatic winds moving through the hellas basin in a clock wise direction parallel to the basin floor outline carved out the northwestern hellas planitia trough called peneus palus possibly within a time span of few hundreds of ma or less within the amazonian being consistent with erosional patterns we observed within the basin circulation models predict such winds to be ongoing today and might thus have recently exhumed the so called honeycomb formation on parts of peneus palus this enigmatic unique terrain was possibly formed by ductile deformation of pre 3 8 ga material and appears to be partially covered by another unique landform the banded terrain although we cannot rule out that it is the surface expression of a thicker unit the banded terrain might represent flows of volatile rich airfall deposits emplaced along the edges of the hellas wind alley by turbulent marginal wind currents which currently recently prevail on both sides of the hellas planitia trough in summary our investigations enabled us to draw an updated comprehensive and self consistent picture of the geologic evolution of the hellas basin floor including volcanic peri glacial fluvial and eolian processes their possible interactions and the implications on the climatic and geologic development of the circum hellas region and the entire planet

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

an active subglacial water system in west antarctica mapped from space satellite laser altimeter elevation profiles from 2003 to 2006 collected over the lower parts of whillans and mercer ice streams west antarctica reveal 14 regions of temporally varying elevation which we interpret as the surface expression of subglacial water movement vertical motion and spatial extent of two of the largest regions are confirmed by satellite image differencing a major previously unknown subglacial lake near the grounding line of whillans ice stream is observed to drain 2 0 cubic kilometers of water into the ocean over 3 years while elsewhere a similar volume of water is being stored subglacially these observations reveal a wide spread dynamic subglacial water system that may exert an important control on ice flow and mass balance

origin and large scale erosional features of glacial lake spillways in the northern great plains deglaciation of the northern great plains produced two basic types of fluvial systems 1 depositional regimes produced by the action of glacial melt water that formed outwash plains and 2 highly erosive systems produced by the sudden rapid drainage of glacial lakes that formed spillways spillways are huge deeply incised trenches that display all of the characteristics of fluvial channels glacial lakes drained in weeks or months and discharges of 10 5 m 3 s were attained at bankfull stage seven spillway systems studied were formed as a consequence of the sudden rapid draining of glacial lakes many other large valleys in the mid continent area and other glaciated regions were probably formed by the same process spillways consist of deeply incised inner channels commonly flanked by broad scoured outer zones initial stages of flow produced shallow anastomosing channels continued erosion produced longitudinal grooves streamlined erosional residuals and surficial boulder lag deposits inner channels developed by the enlargement of one or more centrally located longitudinal grooves the development of erosional residuals was initiated by the incision of shallow anastomosing channels the interchannel areas were progressively modified from irregular quadrilateral or elliptical shapes to an equilibrium minimum drag lemniscate shape as glacial lake drainage proceeded correlations between length and width length and area width and area and length width ratio and k a shape parameter of the lemniscate loop are very high for all erosional residuals studied although only 20 of the residuals display an equilibrium lemniscate shape stable relationships between length width and area of erosional residuals are therefore established very early and are maintained throughout the erosional modification to the lemniscate shape the only shape factor tested which can be used to quantitatively differentiate lemniscate from nonlemniscate erosional residuals is the position of maximum width as measured by the ratio of the length from the lee to the point of maximum width to the total length xm l the mean xm l ratio for erosional residuals in a spillway segment is an indication of the relative duration of flood flows that produced the spillway

the channeled scabland back to bretz comment and reply we thank komatsu et al for their comments on meltwater volumes discharges and depths required to flood areas of the channeled scabland their results are exciting as they demonstrate that using the maximum discharge rate from glacial lake missoula cf o connor and baker 1992 1 the volume

extensive deposits on the pacific plate from late pleistocene north american glacial lake outbursts abstract one of the major unresolved issues of the late pleistocene catastrophic flood events in the northwestern united states e g from glacial lake missoula has been what happened when the flood discharge reached the ocean this study compiles available 3 5 khz high resolution and airgun seismic reflection data long range sidescan sonar images and sediment core data to define the distribution of flood sediment in deepwater areas of the pacific ocean upon reaching the ocean at the mouth of the columbia river near the present day upper continental slope sediment from the catastrophic floods continued flowing downslope as hyperpycnally generated turbidity currents the turbidity currents resulting from the lake missoula and other latest pleistocene floods followed the cascadia channel into and through the blanco fracture zone and then flowed west to the tufts abyssal plain a small part of the flood sediment which was stripped off the main flow at a bend in the cascadia channel at its exit point f

loess paleosol carbonate clumped isotope record of late pleistocene holocene climate change in the palouse region washington state usa the channeled scabland palouse region of the pacific northwest pnw of the united states preserves geomorphic and pedosedimentary records that inform understanding of late pleistocene holocene paleoclimate change in a region proximal to the last glacial period cordilleran ice sheet we present a clumped 47 and conventional 18 o 13 c isotopic study of palouse loess paleosol carbonates in combination with carbonate radiocarbon 14 c dating to provide new measures of regional late last glacial 31 20 cal ka bp and holocene soil conditions average clumped isotope temperatures t 47 for last glacial palouse loess paleosol carbonates 9 4 c are significantly lower than those for holocene aged carbonates t 47 18 2 c in study sections calculated soil water 18 o vsmow values 16 2 for last glacial carbonates are also offset relative to those for holocene aged samples 11 1 whereas calculated soil co 2 13 c vpdb values are similar for the holocene 16 9 0 2 and late last glacial 16 7 1 1 periods together these paleoclimate metrics indicate late last glacial conditions of pedogenic carbonate formation in the c 3 grassland soils of the palouse were measurably colder 9 5 c than during the holocene and potentially reflect a more arid last glacial paleoclimate across the palouse findings in agreement with previous proxy studies and climate model simulations for the region

deep sea sedimentary record of the late wisconsin cataclysmic floods from the columbia river new results from ocean drilling program site 1037 and u s geological survey high resolution seismic reflection profiles confirm the great thickness fast deposition rate distant source and convolute path of turbidites that fill the escanaba trough the rift valley of the southernmost segment of the gorda ridge accelerator mass spectrometry 14 c measurements provide the first direct dating of the escanaba trough turbidites demonstrating an average deposition rate faster than 10 m k y between 32 and 11 ka and as fast as 15 m k y during the oxygen isotope stage 2 lowstand in the upper 60 m of sediment the petrology of turbidite sand beds which are as much as 12 m thick show that the dominant source for the turbidites is from the columbia river which is more than 800 km to the north rather than from the much closer rivers of northern california new high resolution seismic reflection profiles show that except for areas of very recent volcanism the entire escanaba trough below 3200 m water depth is floored by the turbidite sequence that was cored in the upper 60 m at site 1037b the ages of the upper 120 m of turbidites correspond with the ages of channeled scabland deposits associated with latest quaternary jokulhlaups from glacial lake missoula the age and source characteristics suggest that these megaturbidite beds in escanaba trough are most likely deposits formed by hyperpycnally generated turbidity currents as the largest of the lake missoula floods entered the sea

the spokane flood debates historical background and philosophical perspective the 1920s 1930s debates over the origin of the channeled scabland landscape of eastern washington northwestern usa focused on the cataclysmic flooding hypothesis of j harlen bretz during the summer of 1922 bretz began leading field parties of advanced university of chicago students into the region in his first paper published in the bulletin of the geological society of america bretz took special care not to mention cataclysmic origins however in a subsequent paper in the journal of geology to the editorial board of which he had recently been added bretz formally described his hypothesis that an immense late pleistocene flood which he named the spokane flood had derived from the margins of the nearby cordilleran ice sheet this cataclysm neatly accounted for numerous interrelated aspects of the channeled scabland landscape and nearby regions nevertheless the geological community largely resisted bretz s hypothesis for decades despite his enthusiastic and eloquent defence thereof resolution of the controversy came gradually initially through the recognition by j t pardee of a plausible source for the flooding ice dammed pleistocene glacial lake missoula in northern idaho and western montana eventually by the 1960s the field evidence for cataclysmic flooding became overwhelming and physical processes were found to be completely consistent with that evidence the controversy is of philosophical interest in regard to its documentation of the attitudes of geologists toward hypotheses which illustrate aspects of geological reasoning that are distinctive in degree from those of other sciences j harlen bretz there can be no period after the j it was the man s entire first name was born in 1882 he initiated one of the great debates in the history of geomorphology while not revolutionary in its implications the debate is nevertheless instructive for how it illustrates the workings of science where the latter is defined not as a sterile collection of facts or even as a logical application of method but rather as the collective workings and attitudes of human beings passionately dedicated to the search for truth the subject of the debate is an unusual landscape in eastern washington northwestern united states described by bretz 1928a pp 88 89 as follows no one with an eye for land forms can cross eastern washington in daylight without encountering and being impressed by the scabland like great scars marring the otherwise fair face to the plateau are these elongated tracts of bare black rock carved into mazes of buttes and canyons everybody on the plateau knows scabland the popular name is a metaphor the scablands are wounds only partially healed great wounds in the epidermis of soil with which nature protects the underlying rock the region is unique let the observer take wings of the morning to the uttermost parts of the earth he will nowhere

fluvial geomorphology on earth like planetary surfaces a review morphological evidence for ancient channelized flows fluvial and fluvial like landforms exists on the surfaces of all of the inner planets and on some of the satellites of the solar system in some cases the relevant fluid flows are related to a planetary evolution that involves the global cycling of a volatile component water for earth and mars methane for saturn s moon titan in other cases as on mercury venus earth s moon and jupiter s moon io the flows were of highly fluid lava the discovery in 1972 of what are now known to be fluvial channels and valleys on mars sparked a major controversy over the role of water in shaping the surface of that planet the recognition of the fluvial character of these features has opened unresolved fundamental questions about the geological history of water on mars including the presence of an ancient ocean and the operation of a hydrological cycle during the earliest phases of planetary history other fundamental questions posed by fluvial and fluvial like features on planetary bodies include the possible erosive action of large scale outpourings of very fluid lavas such as those that may have produced the remarkable canali forms on venus the ability of exotic fluids such as methane to create fluvial like landforms as observed on saturn s moon titan and the nature of sedimentation and erosion under different conditions of planetary surface gravity planetary fluvial geomorphology also illustrates fundamental epistemological and methodological issues including the role of analogy in geomorphological geological inquiry

turbidite megabeds in an oceanic rift valley recording jokulhlaups of late pleistocene glacial lakes of the western united states abstract escanaba trough is the southernmost segment of the gorda ridge and is filled by sandy turbidites locally exceeding 500 m in thickness new results from ocean drilling program odp sites 1037 and 1038 that include accelerator mass spectrometry ams 14c dates and revised petrographic evaluation of the sediment provenance combined with high resolution seismic reflection profiles provide a lithostratigraphic framework for the turbidite deposits three fining upward units of sandy turbidites from the upper 365 m at odp site 1037 can be correlated with sediment recovered at odp site 1038 and deep sea drilling program dsdp site 35 six ams 14c ages in the upper 317 m of the sequence at site 1037 indicate that average deposition rates exceeded 10 m k yr between 32 and 11 ka with nearly instantaneous deposition of one 60 m interval of sand petrography of the sand beds is consistent with a columbia river source for the entire sedimentary sequence in escanaba trough high resolution acoustic strat

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

status of glacial lake columbia during the last floods from glacial lake missoula abstract the last floods from glacial lake missoula montana probably ran into glacial lake columbia in northeastern washington in or near lake columbia s sanpoil arm lake missoula floods dating from late in the fraser glaciation produced normally graded silt beds that become thinner upsection and which alternate with intervals of progressively fewer varves the highest three interflood intervals each contain only one or two varves and about 200 400 successive varves conformably overlie the highest flood bed this sequence suggests that jokulhlaup frequency progressively increased until lake missoula ended and that lake columbia outlasted lake missoula the upper grand coulee lake columbia s late fraser age outlet contains a section of 13 graded beds most of them sandy and separated by varves that may correlate with the highest missoula flood beds of the sanpoil river valley the upper grand coulee also contains probable correlatives of many of the approximately 200 400 succeeding varves as do nearby parts of the columbia river valley this collective evidence casts doubt on a prevailing hypothesis according to which one or more late fraser age floods from lake missoula descended the columbia river valley with little or no interference from lake columbia s okanogan lobe dam

discontinuous drainage systems formed by highland precipitation and ground water outflow in the navua valles and southwest hadriacus mons regions mars abstract the navua valles are systems of paleodrainages located north of dao vallis which empty into hellas planitia the largest impact basin on mars in this study we mapped and characterized the navua valles region s individual drainage systems including drainages along the southwestern flank of hadriacus mons and one valley network from the same source as navua valles but flowing in the opposite direction the major drainage systems share morphological characteristics common to both outflow channels and valley networks the slopes in this region are dissected by two major navua drainage systems here navua a and b and several shorter sub parallel valleys formed on the highest gradient approximately 20 m km 1 15 slopes at the lowest part of hellas basin s rim the two major drainage systems originate in the highlands and empty into the basin our mapping suggests that water in navua valles reached the basin floor in a complicated descent and included several episodes of surface ponding surface runoff infiltration subsurface flow and subsequent outflow the most prominent channel system navua a forms a repetitive sequence of deep incision into bedrock followed by a transition into broad channels in erodible materials and then into unconfined deposits this successive erosion transport deposition sequence continues to repeat along the valley s entire length forming a discontinuous pattern that is consistent with classical fluvial process models the channels cut into volcanic plains likely emplaced from the formation of tyrrhenus and hadriacus montes the dendritic source valleys of navua a originate from the rim of a highland crater while the rest of this subsystem consists of a single discontinuous channel which is consistent with a single water source zone that likely supplied water for all channels downslope these drainages may have formed as discontinuous channels revealing the potential existence of subsurface drainage pathways located within an approximately 1 5 10 5 km 2 area water transported underground emerged in segments that are either isolated or aligned downslope from each other we have identified several causes of discontinuities located the zones of potential ground water discharge and recharge and a site of localized precipitation at the headwaters of navua a

experimental simulation of channel incision into a cohesive substrate at varying gradients six flume runs using a substrate of 30 bentonite and 70 fine sand were used to examine channel incision into a cohesive homogeneous substrate gradients for the various runs were 1 2 5 10 and 20 other variables remained constant discharge 2 l s sediment discharge averages 3 g s run time 15 with increasing flume gradient bed forms change from parallel longitudinal grooves to a broad shallow channel with weakly undulating bed and walls and then to a progressively deeper and more undulating inner channel downstream changes in reach scale several channel widths gradient may thus be responsible for downstream variability of erosional bed forms in the absence of changes in other controlling variables for bedrock channels it is not necessary to invoke substrate variability to explain the presence of erosional bed forms and associated variations in cross sectional area erosional bed forms may approximate an equilibrium state in which negligible change occurs in bed form dimensions or shape with time downstream alternations between solely erosion and deposition of an alluvial veneer over incisional features occur along channel reaches of constant gradient the downstream length of these alternations is inversely proportional to gradient

evidence for middle amazonian catastrophic flooding and glaciation on mars abstract early geologic investigations of mars revealed some of the largest channels in the solar system outflow channels which appear to have mostly developed 3 byr ago these channels have been the subject of much scientific inquiry since the 1970s and proposed formative processes included surface erosion by catastrophic floods glaciers debris flows and lava flows based on the analysis of newly acquired mars reconnaissance orbiter mro context ctx 5 15 5 91 m pixel and high resolution imaging science experiment hirise 25 50 cm pixel image data we have identified a few locations contained within relatively narrow canyons of the southern circum chryse outflow channels that retain well preserved decameter hectometer scale landform assemblages these terrains include landforms consistent in shape dimension and overall assemblage to those produced by catastrophic floods and at one location to glacial morphologies impact crater statistics for four of these surfaces located within upstream midstream and downstream outflow channel surfaces yield an age estimate of 600 myr this suggests that the southern circum chryse outflow channels were locally resurfaced by some of the most recent catastrophic floods on the planet and that these floods coexisted within regional glacier environments as recently as during the middle amazonian

a continuously weighing high frequency sand trap wind tunnel and field evaluations abstract a new continuously weighing high frequency sand trap cwhf has been designed its sampling efficiency is evaluated in a wind tunnel and the potential of the new trap has been demonstrated in field trials the newly designed sand trap allows fully automated and high frequency measurement of sediment fluxes over extensive periods we show that it can capture the variations and structures of wind driven sand transport processes and horizontal sediment flux and reveal the relationships between sand transport and meteorological parameters its maximum sampling frequency can reach 10 hz wind tunnel tests indicated that the sampling efficiency of the cwhf sand trap varies between 39 2 to 64 3 with an average of 52 5 it achieved a maximum sampling efficiency of 64 3 at a wind speed of 10 m s 1 this is largely achieved by the inclusion of a vent hole which leads to a higher sampling efficiency than that of a step like sand trap at high wind speeds in field experiments we show a good agreement between the mass of sediment from the cwhf sand trap the wind speed at 2 m and the number of saltating particles at 5 cm above the ground surface according to analysis of the horizontal sediment flux at four heights from the cwhf sand trap 25 35 50 and 100 cm the vertical distribution of the horizontal sediment flux up to a height of 100 cm above the sand surface follows an exponential function our field experiments show that the new instrument can capture more detailed information on sediment transport with much reduced labor requirement therefore it has great potential for application in wind blown sand monitoring and process studies

the channeled scabland back to bretz comment and replycomment shaw et al 1999 1 say that only one big flood went through the channeled scabland during the last glaciation they also say this flood did not come from glacial lake missoula they propose that the water flowed southward from a reservoir beneath the cordilleran ice sheet these ideas clash

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

particle comminution defines megaflood and superflood energetics abstract the concept of megafloods and superfloods was introduced at the end of the last century to define exceptionally large discharge floods primarily those associated with the failure of quaternary ice dams these floods exceeded by one or two magnitudes historically recorded floods megafloods having peak discharges equalling or exceeding 1 m m3 s 1 herein the sediment associations of exceptional floods are found to be distinctive being dominated by comminuted smashed grain size distributions which contrast to the sediment deposits of more moderate floods a consideration of the energetics of moderate floods superfloods and megafloods with respect to the entrainment dis entrainment suspension and comminution of coarse gravel allows thresholds of energy expenditure to be proposed that reflect general transformations in flood behaviour that relate to distinctive flood deposits a threshold of energy expenditure 20 kj s 1 m 2 is proposed to separate moderate floods from superfloods the latter by this definition can be 0 1 m m3 s 1 this threshold separates floods competent to entrain cobbles and boulders with limited comminution of the load from superfloods that comminute the suspended cobbles and boulders to produce fine granules in suspension the granules are subsequently deposited to form distinct depositional units that are characteristic of superfloods and megafloods the energetic threshold is consistent with the lower range of power expenditures associated with the original definition of a megaflood in terms of peak fluid flux significance exceptional floods occurred in prehistoric times the largest are referred to as megafloods or superfloods to distinguish such exceptional floods from other large floods megafloods were defined as having a peak discharge exceeding 1 m m3 s 1 however many reports of megafloods are flows with a peak discharge smaller than 1 m m3 s 1 recent research has shown that megafloods and superfloods deposit distinctive layers of smashed gravel which is not the case for smaller floods the gravel is smashed by exceptionally high energy expenditures consideration of the energetics of floods to transport gravel allows a robust quantitative definition of superflood based on the energy needed to smash a range of gravel sizes

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

paleohydrology and flood geomorphology of ares vallis ares vallis is a martian outflow channel which is about 1500 km long and locally exceeds 100 km in width and 1000 m in depth we estimate the channel s paleoflow capacity using paleohydraulic techniques at a constricted and unusually deep reach not affected by tributaries or secondary inflows the estimated possible maximum peak discharges are of the order of 108 109 m3 s these values are 1 to 2 orders of magnitude larger than any known terrestrial floods these high discharge flows were theoretically capable of transporting boulders larger than 10 m in diameter the downstream depositional plain where ares debauches into the chryse planitia displays geomorphological features indicative of high erosional capacity by the flooding in this area site of the proposed pathfinder landing we expect to find a complex sequence of sediments created by varying paleoflood flow hydraulics sediment transport characteristics and probable secondary modification of the primary flood landforms

flood geomorphology of the katherine gorge northern territory australia the katherine gorge is a narrow deep canyon system developed in resistant sandstone the tropical monsoonal climate results in rare flood events of very large magnitude these floods flush sand sized sediment as washload through the gorge but local accumulations are preserved as slack water deposits at tributary mouths paleoflood hydrologic analysis of the deposits employing step backwater flow modeling allows quantitative estimates to be made of geomorphically significant flows for an annual exceedence probability of 10 2 the gorge may experience discharges of 6 000 m 3 s mean velocities of 7 5 m s flow depths of 15 to 45 m stream powers per unit area as great as 1 10 4 watts m 2 and bed shear stresses of 1 5 10 3 n m 2 such flows are required to transport boulders 3 m or more in intermediate diameter that occur at large scale riffles at maximum stage pools reach depths of 45 m and are preferentially developed at vertical joint intersections in the rock probably through intense hydraulic action pool and riffle development thus reflects the channel boundary characteristics for extreme flow conditions additional indicators of especially intense flow phenomena include potholes flutes abraded facets on rock bar surfaces and scabland development on upland bedrock surfaces

correlation of distal tephra layers in loess in the channeled scabland and palouse of washington state abstract thirty two distal tephra layers that are interbedded in quaternary loess at 13 sites in the channeled scabland and palouse were sampled as part of a regional study of the stratigraphy and chronology of dominantly windblown sediments on the columbia plateau an electron microprobe was used to determine the elemental composition of volcanic glass in all of the samples and also to determine the composition of ilmenite in 14 of them two of the distal tephra layers correlate with glacier peak eruptions 11 200 yr b p five with mount st helens tephra set s 13 000 yr b p and nine with mount st helens tephra set c ca 36 000 yr b p based on analysis of glass and ilmenite in reference pumices from glacier peak mount st helens mount mazama mount rainier and mount jefferson on the calculation of similarity coefficients for comparisons of both glass and ilmenite reference compositions with those of distal tephras and on considerations of stratigraphic position the composition of glass and ilmenite and the stratigraphic position of one distal tephra layer in the loess suggests that it is from an eruption of mount st helens at least several thousand years older than the set c eruptions glass composition and stratigraphic position of a distal tephra at another site in loess suggested a possible correlation with some layers of the pumice castle eruptive sequence at mount mazama ca 70 000 yr b p but similarity coefficients on ilmenite of only 45 and 48 fail to support the correlation and show why multiple correlation methods should be used similarity coefficients higher than 96 for both glass and ilmenite establish a correlation with mount st helens layer cw for distal layers in two widely separated sites these layers are in sedimentary successions that are closely associated with giant floods in the channeled scabland the 36 000 yr b p radiocarbon age of the mount st helens set c establishes a minimum limiting date for an episode of flooding that predates the widespread late wisconsin floods a correlation of distal tephra layers at two other sites in the scabland and palouse establishes a chronostratigraphic link to a still older episode of flooding within the brunhes normal polarity chron six distal tephra layers in pre late quaternary loess that are not correlated with known or dated eruptions have compositions and distinctive stratigraphic positions relative to magnetic reversal boundaries that make them key markers for future work

catastrophic flooding origin of shelf valley systems in the english channel britain became geographically isolated from continental europe when high interglacial seas flooded the shallow english channel and north sea shelf areas but a tenuous link remained the weald artois chalk ridge between southeast england and northwest france just how this isthmus was breached making britain an island has been a matter of conjecture a new bathymetric map of the sea floor may solve the mystery it reveals a large bedrock floored valley containing landforms including grooves and streamlined islands consistent with a megaflood event caused when a rock dam at the dover strait breached draining a large pro glacial lake in the north sea basin a hypothesis for the permanent isolation of britain from mainland europe during interglacial high sea levels has been confirmed gupta et al analysed a new regional bathymetric map of part of the area finding a valley with landforms indicating large scale subaerial erosion by high magnitude water discharges they suggest breaching of a rock dam at the dover strait instigated drainage of a large lake in the north sea basin megaflood events involving sudden discharges of exceptionally large volumes of water are rare but can significantly affect landscape evolution continental scale drainage patterns and climate change1 it has been proposed that a significant flood event eroded a network of large ancient valleys on the floor of the english channel the narrow seaway between england and france2 3 4 this hypothesis has remained untested through lack of direct evidence and alternative non catastrophist ideas have been entertained for valley formation5 6 here we analyse a new regional bathymetric map of part of the english channel derived from high resolution sonar data which shows the morphology of the valley in unprecedented detail we observe a large bedrock floored valley that contains a distinct assemblage of landforms including streamlined islands and longitudinal erosional grooves which are indicative of large scale subaerial erosion by high magnitude water discharges our observations support the megaflood model in which breaching of a rock dam at the dover strait instigated catastrophic drainage of a large pro glacial lake in the southern north sea basin2 we suggest that megaflooding provides an explanation for the permanent isolation of britain from mainland europe during interglacial high sea level stands7 and consequently for patterns of early human colonisation of britain together with the large scale reorganization of palaeodrainage in northwest europe4

thermoluminescence dating of late pleistocene loess and tephra from eastern washington and southern oregon and implications for the eruptive history of mount st helens the first numeric dating of late pleistocene loess from the palouse region of eastern washington is reported this loess is interbedded with thin distal tephra layers some identified as mount st helens products both the interbedded tephra layers and thick paleosols that have developed in the loess have previously been correlated across the region a thicker correlative of one of these tephra layers mount st helens set c was collected from summer lake oregon for direct dating by thermoluminescence tl polymineral fine grain tl ages for loess from three chosen sections in washington range from 17 to 83 ka these imply ages for some tephra beds that are significantly older than implied by earlier radiocarbon 14c dating for example tl ages of 17 21 ka for loess bracketing a tephra layer correlated to mount st helens set s suggests a somewhat older age for this ash than the previously accepted 14c age of 15 5 0 5 ka cal yr corrected to calendar years tl ages of 46 6 1 ka and 57 7 ka for loess above and of 53 7 ka and 75 6 ka below a tephra bed correlated to a mount st helens set cw layer along with a tl age of 46 5 ka for fine silt sized glass from a mount st helens set cy bed in oregon revise upward from 38 ka cal yr 14c age is 36 ka b p to 50 ka the age of this regionally important marker ash set several tl ages taken together imply a much longer eruptive history for mount st helens than previously thought a tl age of 83 8 ka just below a previously undated tephra layer from mount st helens emsh ash suggests that the eruptive history of the mountain extends back to at least 80 ka furthermore age depth extrapolation through our sections to an ash wa 5c probably correlated to mount st helens suggests an eruptive history of at least 120 ka

energy expenditure and geomorphic work of the cataclysmic missoula flooding in the columbia river ggorge usa cataclysmic releases from the glacially dammed lake missoula producing exceptionally large floods have resulted in significant erosional processes occurring over relatively short time spans erosional landforms produced by the cataclysmic missoula floods appear to follow a temporal sequence in many areas of eastern washington state this study has focused on the sequence observed between celilo and the john day river where the erosional features can be physically quantified in terms of stream power and geomorphic work the step backwater calculations in conjunction with the geologic evidence of maximum flow stages indicate a peak discharge for the largest missoula flood of 10 10 6 m 3 s 1 the analysis of local flow hydraulics and its spatial variation were obtained calculating the hydrodynamic variables within the different segments of a cross section the nature and patterns of erosional features left by the floods are controlled by the local hydraulic variations therefore the association of local hydraulic parameters with erosional and depositional flood features was critical in understanding landform development and geomorphic processes the critical stream power required to initiate erosion varied for the different landforms of the erosional sequence ranging from 500 w m 2 for the streamlined hills up to 4500 w m 2 to initiate processes producing inner channels erosion is possible only during catastrophic floods exceeding those thresholds of stream power below which no work is expended in erosion in fact despite the multiple outbursts which occurred during the late pleistocene only a few of them had the required magnitude to overcome the threshold conditions and accomplish significant geomorphic work 1997 by john wiley sons ltd

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

long history of pre wisconsin ice age cataclysmic floods evidence from southeastern washington state abstract cataclysmic ice age floods in the pacific northwest began as early as 1 5 2 5 ma on the basis of an evaluation of surface exposures and recent borehole studies within southeastern washington field evidence suggests at least two episodes of pre wisconsin i e 130 ka glacial outburst flooding a middle pleistocene flood is identified by normal magnetic polarity calcrete capped deposits that yield maximum th u age dates from 200 to 400 ka the deposits with reversed polarity are correlated to early pleistocene 780 ka floods while exposures of pre wisconsin deposits are limited because of erosion and or burial the record of earlier pleistocene flooding is preserved within giant flood bars these bars show incremental growth representing a composite from cataclysmic floods deposited intermittently through the pleistocene in one giant flood bar up to 100 m thick deposits interpreted as matuyama age indicate that the bar had grown to half its present height by 780 ka furthermore matuy

shapes of streamlined islands on earth and mars experiments and analyses of the minimum drag form streamlined islands in rivers and comparable landforms in the channeled scabland of washington and in the outflow channels on mars have shapes that are closely similar to symmetrical airfoils with length width ratios averaging 3 to 4 a review of measurements of drag on airfoils demonstrates that a minimum total drag is achieved at such length width ratios supporting the hypothesis that these islands acquired shapes that minimized the drag or resistance to the flowing fluid when they were formed this minimum drag is achieved by the reduction of the wake while maintaining a small skin friction flume experiments were undertaken with model islands to examine how they achieve their streamlined form when the island is not fully submerged a combined bow wave and hydraulic drop play a major role in their erosion but most of the streamlining is brought about by deposition filling the wake region when the island is submerged the flow over the top can become supercritical producing a hydraulic jump in the island lee and focusing the erosion in that region rapidly eroding the island to a streamlined shape these experiments are consistent with the prototype streamlined islands duplicating many of their features

paleomagnetic and tephra evidence for tens of missoula floods in southern washington paleomagnetic secular variation and a hiatus defined by two tephra layers confirm that tens of floods from glacial lake missoula montana entered washington s yakima and walla walla valleys during the last glaciation in these valleys the field evidence for hiatuses between floods is commonly subtle however paleomagnetic remanence directions from waterlaid silt beds in three sections of rhythmically bedded flood deposits at zillah touchet and burlingame canyon display consistent secular variation that correlates serially both within and between sections the secular variation may further correlate with paleomagnetic data from fish lake oregon and mono lake california for the interval 12 000 17 000 14 c yr b p deposits of two successive floods are separated by two tephras derived from mount st helens washington the tephras differ in age by decades indicating that a period at least this long separated two successive floods the beds produced by these two floods are similar to all of the 40 beds in the slack water sediment sequence suggesting that the sequence is a product of tens of floods spanning a period of perhaps a few thousand years

evidence of multiple late wisconsin floods from glacial lake missoula in badger coulee washington abstract catastrophic floods from glacial lake missoula entered the pasco basin in south central washington and backflooded its marginal valleys badger coulee one such valley contains beds of fine grained slackwater sediment deposited by these floods the slackwater sediment contains two ash layers of the mount st helens set s tephra about 13 000 yr old the ash was deposited on a ground surface developed atop slackwater sediment deposited during preash flooding evidence of the former ground surface includes the reworked ash inferred trace fossils stream and debris flow deposits slopewash and or eolian sediment and colluvium at the ash horizon these features and the ash were buried by slackwater sediment deposited during postash flooding nonflood subaerial deposits are not present atop other beds instead beds commonly are reversely graded across contacts suggesting that multiple beds were continuously deposited the exposed beds thus record at least two late wisconsin floods one preash the other postash the pre and postash floods may be correlative with earlier reported floods thought to have occurred 17 500 14 000 and 14 000 13 000 yr b p respectively

the channeled scabland a retrospective the channeled scabland of east central washington in the united states is a complex of anastomosing rock cut fluvial channels cataracts loess islands rock basins broad gravel deposits and immense gravel bars in the 1920s j harlen bretz demonstrated that the channeled scabland formed by cataclysmic erosion and deposition from pleistocene megaflooding derived from the margins of the cordilleran ice sheet particularly glacial lake missoula in western montana and northern idaho studies of this region and the high energy flood processes that generated it are stimulating a discoveries of similar megaflood related landscapes around the world and on mars b enhanced understanding of the processes involved in the fluvial erosion of bedrock and c the use of paleoflood indicators for understanding the magnitudes and frequency of flooding

catastrophic flood sediments in chryse basin mars and quincy basin washington application of sandar facies model viking visible and thermal infrared observations and terrestrial catastrophic flood deposits provide clues to identify the outflow channel sediments that went into chryse basin on mars on earth sandar outwash plains formed by coalescence of many jokulhlaup floods are described in terms of three laterally adjacent facies proximal midfan and distal the missoula flood sediments deposited in quincy basin washington comprise a miniature analog of chryse basin the terminology and general characteristics of the sandar facies model are applied to quincy basin although the depositional environment and clast sizes are somewhat different higher energy flood larger clasts subaqueous rather than subaerial deposition for example the ephrata fan a deposit of boulders cobbles and pebbles forms the midfan facies analog a downfan sandy deposit reworked into a dune field comprises the distal facies analog in chryse basin the midfan is defined by a heterogeneous rocky 0 25 intermediate albedo 0 21 0 26 intermediate thermal inertia 260 460 j m 2 s 0 5 k 1 surface while the distal facies has a low albedo 0 14 0 16 and higher thermal inertia 340 700 j m 2 s 0 5 k 1 the chryse midfan unit has rocks and windblown dust exposed at the surface the sand of the distal facies in chryse acidalia is reworked by the wind as in quincy basin the viking 1 and mars pathfinder landing sites are located on the midfan unit observations that can be made at the mars pathfinder site might help in reevaluating whether or not viking 1 landed on outflow channel sediments

formation of hrad vallis mars by low viscosity lava flows abstract hrad vallis is a martian outflow channel previously interpreted as a product of aqueous outbursts from the subsurface possibly involving mudflows associated with lahar like events however an alternative volcanic hypothesis for the development of the system is worthy of consideration on the basis of 1 the nature of landforms preserved along component channels and adjacent uplands and 2 similarities between the basic properties of this system and large volcanic channels of the inner solar system hrad vallis commences on the distal flanks of the elysium mons shield volcano terminates within extensive volcanic plains is associated with landforms typical of large volcanic channels and shows evidence for having been a conduit for large volumes of lava the properties of this system are consistent with incision by low viscosity lava crude thermal estimates suggest that this system could have formed through effusion of as little as 10 900 km 3 of magma to the surface or 6 of the volume of the terrestrial columbia river basalt group incision rates of up to several meters per day are estimated for mechanical and thermal processes involving lava flows with depths of 5 20 m and dynamic viscosities of 1 pa s flow of lava within the hrad vallis system is predicted to have been fully turbulent and characterized by discharges as great as 865 000 m 3 s predicted flow conditions are consistent with those previously determined for athabasca valles which also formed as a result of the expulsion of flows from structures associated with elysium mons

glacial lake evolution and atlantic pacific drainage reversals during deglaciation of the patagonian ice sheet abstract modelling experiments of drainage events from proglacial lakes of the rio baker catchment central patagonia 46 48 s indicate that atlantic pacific drainage reversals may have caused freshwater forcing of regional climate however much of the region remains unmapped in detail and available geochronological data is equivocal leading to multiple published palaeolake evolution models we evaluate these models through new geomorphological mapping from the baker valley cosmogenic dating of moraine boulders that demonstrates an antarctic cold reversal ice readvance that blocked drainage through the rio baker an altitudinal based review of published geochronology and regional analysis of shoreline glacio isostasy and palaeolake levels we use these datasets to present a new regional palaeolake evolution model underpinned by bayesian age modelling we demonstrate that 103 km3 of freshwater was released to the pacific over at least 6 drainage events from before 15 3 15 0 cal yr bp to the early holocene the final stages of lake drainage involved catastrophic flooding along the baker valley evidenced by high magnitude flood landforms such as boulder bars likely caused by failure of large valley floor moraine dams we place these drainage events in the context of late quaternary meltwater pathways associated with advance retreat of the patagonian ice sheet and early human occupation across the region although broad patterns of ice retreat and lake formation may be similar across patagonia driven by southern hemisphere palaeoclimate regional topographic settings likely resulted in spatial and temporal heterogeneity of atlantic pacific drainage reorganisation across southernmost south america