catastrophic glacial lake outburst flooding of the patagonian ice sheet abstract reconstructing the magnitude and timing of catastrophic drainage of proglacial lakes during late quaternary deglaciation of palaeo ice sheets is important for understanding rates of landscape change and regional freshwater forcing of ocean currents here we provide the first detailed reconstruction of catastrophic glacial lake outburst flooding from the southern hemisphere focusing on the rio baker catchment in central patagonia firstly we review the evidence for palaeolake drainage events in the baker catchment showing the basin witnessed a number of events during late quaternary deglaciation these floods helped re establish the pacific drainage pathway of the rio baker by 12 6 11 7 ka after millennia blocked by ice during the last glaciation secondly we analyse the landform record and flow hydraulics of a catastrophic flood in patagonia focusing on the final early holocene drainage event of lago general carrera buenos aires using two independent methods a one dimensional hydraulic model and dam break simulation we estimate a minimum peak discharge of 110 000 m3s 1 0 1 sv large enough to form megaflood type landforms using the flow hydrograph we constrain timing of landform genesis eddy bars at the top of the water column 45 65 m above the valley floor were inundated over 2 36 h following the breach while tractive bars formed beneath 20 m of water at sites of valley expansion were flooded for 100 h raised deltas and palaeoshorelines provide geomorphic evidence for palaeolake drainage events across patagonia indicating the likely role that catastrophic floods played in continental scale palaeohydrology and the evolution of fjord ecosystems

high latitude lower thermospheric neutral winds at eiscat and sondrestrom during ltcs 1 the incoherent scatter radar located at sondre stromfjord greenland 67 n 51 w 74 5 and the eiscat incoherent scatter facility located in northern scandinavia 69 5 n 19 e 66 3 both obtained e and f region measurements during the first campaign of the lower thermosphere coupling study ltcs 1 september 21 25 1987 neutral winds deduced from these measurements have been analyzed for their mean flow and tidal components a number of the altitude profiles for the mean winds and the diurnal and semidiurnal wave components at the two radar locations show similar variations with height indicating that latitudinal rather than longitudinal effects are dominant in determining the observed wind field diurnal tidal amplitudes and phases are reasonably well represented by theoretical model results forbes 1982 the semidiurnal amplitudes and phases although somewhat consistent between the two radars are not well represented in equinox tidal model results forbes and vial this issue results from both radars indicate a vertical wavelength for the zonal semidiurnal oscillation of approximately 60 km during a period of impulsive magnetospheric forcing september 22 23 winds deduced from measurements at both radars show enhanced eastward flows near midnight accompanied by equatorward winds at sondrestrom comparison with the results of a national center for atmospheric research thermosphere ionosphere general circulation model tigcm simulation of the ltcs 1 interval shows generally better agreement with the observations at eiscat than at sondrestrom during the period of activity on september 22 23 the tigcm is reasonably successful at simulating the eastward surge near midnight in the eiscat but not in the sondrestrom observations and the equatorward flow after midnight in the sondrestrom results the observed winds in magnetic latitude and magnetic local time coordinates indicate the presence of anticyclonic divergent flow near dusk and cyclonic converging flow near dawn

the sequence and timing of large late pleistocene floods from glacial lake missoula abstract glacial lake missoula formed when the purcell trench lobe of the cordilleran ice sheet dammed clark fork river in montana during the fraser glaciation marine oxygen isotope stage 2 over a period of several thousand years the lake repeatedly filled and drained through its ice dam and floodwaters coursed across the landscape in eastern washington in this paper we describe the stratigraphy and sedimentology of a significant new section of fine grained glacial lake missoula sediment and compare this section to a similar previously described sequence of sediments at ninemile creek 26 km to the northwest the new exposure which we informally term the rail line section is located near missoula montana and exposes 29 units each of which consists of many silt and clay couplets that we interpret to be varves the deposits are similar to other fine grained sediments attributed to glacial lake missoula similar varved sediments overlie gravelly flood deposits elsewhere in the glacial lake missoula basin each of the 29 units represents a period when the lake was deepening and all units show evidence for substantial draining of glacial lake missoula that repeatedly exposed the lake floor the evidence includes erosion and deformation of glaciolacustrine sediment that we interpret happened during draining of the lake desiccation cracks that formed during exposure of the lake bottom and fluvial sand deposited as the lake began to refill the floods date to between approximately 21 4 and 13 4 cal ka ago based on regional chronological data the total number of varves at the rail line and ninemile sites are respectively 732 and 583 depending on lake refilling times each exposure probably records 1350 1500 years of time we present three new optical ages from the rail line and ninemile sites that further limit the age of the floods these ages in calendar years are 15 1 0 6 ka at the base of the ninemile exposure and 14 8 0 7 and 12 6 0 6 ka midway through the rail line exposure the sediment at the two sections was deposited during later stages of glacial lake missoula after the largest outburst events

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

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

tracking fluvial response to climate change in the pacific northwest a combined provenance approach using ar and nd isotopic systems on fine grained sediments traditional provenance techniques nd isotopes and clay mineralogy are combined with recently developed bulk sediment 40 ar 39 ar radiometric methods to determine how the terrestrial sources of sediment to the oregon continental margin have changed over the last 25 000 years both pacific northwest river borne detritus and sediment from piston coring site ew9504 17pc 2671 m water depth offshore southern oregon have been analyzed nd isotopic analyses of river silts show a range of 10 units in end north of the core site the columbia river has end 7 6 while the coos river has a value of end 10 8 rivers proximal to the core site have more radiogenic values from north to south of end 5 0 umpqua river end 1 3 rogue river end 0 6 klamath river and end 3 0 eel river measured end in core sediments show subtle downcore changes between end 0 9 and 2 5 the bulk sediment 40 ar 39 ar plateau ages show more notable downcore variation between 25 and 14 ka ranging from 113 5 to 124 0 ma but are still within the range of bulk ages previously measured on river mouth sediments the nd isotopic analyses are combined with bulk sediment 40 ar 39 ar plateau ages into a ternary mixing model to quantitatively assess the sources of terrigenous material mixtures are best described by three sources proximal to the core site the umpqua rogue klamath and eel rivers from 14 ka to present sediment deposited in the interval from 22 to 25 ka is not adequately described by the present day rivers and requires an additional source this additional source is best explained by an enhanced contribution from the interior cascade volcanic arc probably due to glaciation in the cascade range and the presence of pluvial lake modoc in the upper klamath basin at this time from 22 to 14 ka the influence of cascade range sediment at the core site was overprinted by contemporaneous glaciation and sediment production in the klamath mountains and possibly addition of sediment from the eel river region as well thus differential erosion appears to play a primary role in the provenance changes seen at the core site and is more significant than sediment transport changes due to ocean circulation during this time period overall the combined ar nd isotopic technique provides insight into the coupling of land surface processes and ocean circulation related to climate change and will be a useful provenance tool in a variety of geologic climatic settings r 2007 elsevier ltd all rights reserved

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

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

10be dating of late pleistocene megafloods and cordilleran ice sheet retreat in the northwestern united states during the late pleistocene multiple floods from drainage of glacial lake missoula further eroded a vast anastomosing network of bedrock channels coulees and cataracts forming the channeled scabland of eastern washington state united states however the timing and exact pathways of these missoula floods remain poorly constrained thereby limiting our understanding of the evolution of this spectacular landscape here we report cosmogenic 10 be ages that directly date flood and glacial features important to understanding the flood history the evolution of the channeled scabland and relationships to the cordilleran ice sheet cis one of the largest floods occurred at 18 2 1 5 ka flowing down the northwestern columbia river valley prior to blockage of this route by advance of the okanogan lobe of the cis which dammed glacial lake columbia and diverted later missoula floods to more eastern routes through the channeled scabland the okanogan and purcell trench lobes of the cis began to retreat from their maximum extent at ca 15 5 ka likely in response to onset of surface warming of the northeastern pacific ocean upper grand coulee fully opened as a flood route after 15 6 1 3 ka becoming the primary path for later missoula floods until the last ones from glacial lake missoula at 14 7 1 2 ka the youngest dated flood s 14 0 1 4 ka to 14 4 1 3 ka came down the northwestern columbia river valley and were likely from glacial lake columbia indicating that the lake persisted for a few centuries after the last missoula flood

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

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

sondrestrom incoherent scatter radar observations during the lower thermosphere coupling study september 21 26 1987 the incoherent scatter radar located at soendre stroemfjord greenland obtained e and f region measurements during the first lower thermosphere coupling study ltcs 1 september 21 26 1987 lower thermospheric neutral winds deduced from these measurements show that the neutral dynamics are influenced by both tidal oscillations and magnetospheric forcing during an interval which was relatively quiet geomagnetically september 23 24 a semidiurnal oscillation dominated the neutral motion the model equinox tidal amplitudes and phases of forbes 1982 for the diurnal tide are roughly in agreement with the observed diurnal oscillation for the first four days of the experiment vertical variations in the observed diurnal phases are consistent with the results of forbes and hagan 1988 and may provide evidence of dissipation of the propagating 1 1 tidal mode the semidiurnal motion observed during this period is not well represented by the recent theoretical results for the amplitude and phase of the semidiurnal tide forbes and vial this issue neutral winds obtained during a geomagnetically active interval september 25 26 displayed a flow pattern that was significantly distorted from that observed during the preceding relatively quiet interval although the changes in the zonal winds throughout this active interval were consistent with the directionmore of the ion drag force at 115 km and above the variations in the meridional winds suggest that other forces such as pressure gradients driven by joule heating need to be considered to explain the observations less

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

mesosphere thermosphere tidal coupling during the september 21 25 1987 ltcs 1 campaign the thermosphere ge 90 km is dynamically coupled to the mesophere and lower atmospheric regions by gravity waves tides and planetary waves which propagate upward from below and often undergo dissipation in the 80 to 150 km region this paper focuses on the mesosphere thermosphere coupling due to the solar semidiurnal atmospheric tide during the first lower thermosphere coupling study ltcs campaign interval of september 21 25 1987 during this period determinations of semidiurnal eastward u and northward v velocity components and temperature delta t are available within the 80 to 150 km region from a total of 13 incoherent scatter meteor and spaced antenna radars a new method is developed and reported here for assimilating such data sets into a self consistent global empirical description of the tidal dynamics between 80 and 150 km using a set of numerically generated hough mode extension hme functions for u v and delta t corresponding to the 2 2 2 3 2 4 and 2 5 semidiurnal tidal modes a least squares fit to the radar data is performed the fit results in a single complex normalizing factor for each hme from which globally continuous and internally consistent semidiurnal oscillations in u v and delta t as well as vertical velocity and density canmore be derived the quality of fit to these data from various height regions including both northern and southern hemispheres establishes the internal consistency between these measurements as well as the applicability of the method to future data sets the resulting empirical model reproduces the data significantly better than recent theoretical models suggesting use of the method for deriving tidal boundary conditions for thermospheric general circulation models less

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

thermospheric extensions of the classical expansion functions for semidiurnal tides solutions to the thermospheric tidal equations are described that define the extensions into the thermosphere of normalized wind and temperature structures associated with the 2 2 2 3 2 4 and 2 5 semidiurnal propagating tidal modes sample figures are presented that illustrate the degree of alteration of vertical structures with latitude and the change in horizontal shapes with height corresponding to semidiurnal oscillations in northerly westerly and vertical velocity and temperature in the thermosphere additional figures and tables covering the 80 to 400 km altitude region for five levels of solar activity at 6 latitude increments are available on microfiche for potential users the structures can be used to extend meteor wind 80 100 km and partial reflection drift 60 100 km measurements to heights above 100 km for consistency checks with tidal winds and temperatures from thomson scatter measurements at possibly different latitudes or to simultaneously fit data covering these height regions for modeling purposes supplementary figures and tables are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20002 document j82 003 1 00 payment must accompany order

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

composition age and depositional rates of shoreface deposits under barriers and beach plains of the columbia river littoral cell usa abstract the columbia river littoral cell crlc consists of four subcells totaling 160 km in length that are unique in the west coast of the united states in that they contain prograded barriers and beach plains reaching 0 5 3 km in width fig 1 the prograded beach deposits 1 5 ka in age overlie shoreface deposits 1 8 ka in age as identified in 18 ground penetrating radar profiles and sampled from 24 boreholes two competing hypotheses were initially proposed to account for the origins of these unique progradative shorelines 1 cross shore feeding by onshore wave transport of pre holocene sand from the submerged shelf and 2 longshore dispersal of nearshore sand that was supplied to the littoral system by bedload sediment discharge from the columbia river during the holocene the crlc sand forming the shoreface deposits is fine diameter 0 2 0 02 mm and rich in lithic fragments 20 40 by volume gravel and shell lag layers are uncommon in most of the crlc shoreface deposits but they show greater abundance locally near ravinement surfaces tidal inlets and in the clatsop subcell located south of the columbia river mouth gravel and granule layers increase upsection in barriers south of the columbia river and downsection in barriers at the northern end of the littoral system these trends suggest different mechanisms of shoreface sediment feeding within the four subcells however borehole samples from all four subcells show the same sand provenance i e post glacial columbia river sand which is identified by high ratios of hypersthene augite in heavy mineral fractions selected shoreface sections were dated 0 5 8 ka by ams radiocarbon analysis of articulated shell and wood fragments recovered from auger flights 3 22 m depth subsurface relatively young shoreface deposition 2 5 ka at 6 5 m elevation ngvd88 in the clatsop subcell south of the columbia river shows a net southward beach transport that fed shoreface and beachface progradation into deeper water older and deeper shoreface deposition 4 4 ka at 7 1 m elevation in the long beach subcell north of the columbia river was a result of the filling of innermost shelf accommodation space prior to beachface progradation the total volume of shoreface sand deposited under the barrier spits and beach plains of the crlc is estimated to be 6 7 km3 deposited since 6 8 ka there was a net northward transport of littoral sand 1 106 m3 year 1 along the nearshore and inner shelf subsequently some of this sand was transported onshore to feed beaches of the northernmost subcells columbia river sand was also the source for the formation of the offshore shelf wedge above the transgressive ravinement surface and for the filling of major tidal basins located north of the columbia river in summary the unique progradational history of the crlc barriers and beach plains derives from the combination of 1 longshore dispersal of fine sand discharged from the columbia river during holocene time and 2 across shore feeding of beaches at the northern end of the littoral system from fine sand carried north along the nearshore and the inner shelf

on the coupling between the lower and the upper thermosphere during the first lower thermosphere coupling study simultaneous observations of the neutral winds and temperatures and electron densities in the upper and lower thermosphere are presented the measurements were made at arecibo and millstone hill during the first lower thermosphere coupling study ltcs 1 campaign in september 1987 the observations show a great deal of day to day variability possibly due to the geomagnetic activity which occurred during the period storm effects are discernible in the data at low altitudes near 120 km even at low latitudes near 18 n theoretical simulations of the period were attempted by the national center for atmospheric research thermosphere ionosphere general circulation model a novel development was the use in the model of lower boundary conditions representative of the upward propagating semidiurnal tides based on the ltcs 1 mesosphere lower thermosphere observations the upward propagating diurnal 1 1 mode was also included in the model simulations of the low and mid latitudes did not substantially improve with the use of lower boundary conditions derived from the measurements the model was also unable to reproduce the observations in both the lower and upper thermosphere this may be partially due to the effects of geomagnetic activity on the atmospheric fields since the observational period included two intervals of geomagnetic disturbances in the lower thermosphere resolution of the discrepancies between the data and model predictions may require the extension of the model to lower altitudes at present the model predictions in the lower thermosphere are strongly dependent on the lower boundary conditions the model predicts that diurnal waves are not negligible in analysis of lower thermosphere data indeed near 100 km at the model location of arecibo the diurnal wave amplitudes of the meridional winds were predicted to be greater than the semidiurnal investigation of the model predictions awaits the development of techniques to obtain observations of at least 24 hours duration in the lower thermosphere and the extension of the theoretical models to lower altitudes

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

pre and post missoula flood geomorphology of the pre holocene ancestral columbia river valley in the portland forearc basin oregon and washington usa abstract geomorphic landscape development in the pre holocene ancestral columbia river valley 1 5 km width in the portland forearc basin 50 km length is established from depositional sequences which pre date and post date the glacial lake missoula floods the sequences are observed from selected borehole logs 150 in number and intact terrace soil profiles 56 in number in backhoe trenches four sequences are widespread including 1 a vertically aggraded pleistocene alluvial plain 2 a steep sided valley that is incised 125 150 m into the pleistocene gravel plain 3 missoula flood terraces 19 13 ka abandoned on the sides of the ancestral valley and 4 holocene flooding surfaces 11 8 ka buried at 70 30 m depth in the axial columbia river valley weathering rims and cementation are used for relative dating of incised pleistocene gravel units soil development on the abandoned missoula flood terraces is directly related to terrace deposit lithology including thin bw horizons in gravel irregular podzols in sand and multiple bw horizons in thicker loess capping layers radiocarbon dating of sand and mud alluvium in the submerged axial valley ties holocene flooding surfaces to a local sea level curve and establishes holocene sedimentation rates of 1 5 cm year 1 during 11 9 ka and 0 3 cm year 1 during 9 0 ka the sequences of pleistocene gravel aggradation river valley incision cataclysmic missoula flooding and holocene submergence yield complex geomorphic landscapes in the ancestral lower columbia river valley

coordinated incoherent scatter radar observations of the semidiurnal tide in the lower thermosphere the incoherent scatter radars at arecibo 18 3 degree n millstone hill 42 6 degree n and sondrestrom 67 degree n simultaneously observed the thermal structure and dynamics of the earth s lower thermosphere during the period september 21 25 1987 as part of the lower thermosphere coupling study plasma spectral measurements were used to derive ion temperatures and horizontal neutral wind velocities in the altitude region 90 140 km and semidiurnal harmonics were determined from the data sets the daily mean temperatures were found to be within 40 degree k at the three stations and the largest semidiurnal temperature amplitudes exceeding 70 degree k above 115 km were recorded at arecibo mean winds were about plus minus 30 m s at most altitudes shifting from eastward to westward directions at 115 km and the semidiurnal amplitudes were in the range 20 70 m s phase variations with height reveal reasonable consistency among the three stations within 3 4 hours and indicate an average vertical wavelength of 40 70 km however a strong variation is seen in the vertical structure in the 110 to 130 km region suggesting the presence of different tidal modes comparison with the most current tidal propagation model by forbes and vial this issue indicates that the model tends to underestimate the amplitudes for this time period particularlymore above 110 km by virtue of the latitudinal distribution of the three radars their coordinated observations of the lower thermosphere serve to constrain numerical models and improve their understanding of this important yet complex region of the atmosphere less

late pleistocene outburst flooding from pluvial lake alvord into the owyhee river oregon abstract at least one large late pleistocene flood traveled into the owyhee river as a result of a rise and subsequent outburst from pluvial lake alvord in southeastern oregon lake alvord breached big sand gap in its eastern rim after reaching an elevation of 1292 m releasing 11 3 km 3 of water into the adjacent coyote basin as it eroded the big sand gap outlet channel to an elevation of about 1280 m the outflow filled and then spilled out of coyote basin through two outlets at 1278 m and into crooked creek drainage ultimately flowing into the owyhee and snake rivers along crooked creek the resulting flood eroded canyons stripped bedrock surfaces and deposited numerous boulder bars containing imbricated clasts up to 4 1 m in diameter some of which are located over 30 m above the present day channel critical depth calculations at big sand gap show that maximum outflow from a 1292 to 1280 m drop in lake alvord was 10 000 m 3 s 1 flooding became confined to a single channel approximately 40 km downstream of big sand gap where step backwater calculations show that a much larger peak discharge of 40 000 m 3 s 1 is required to match the highest geologic evidence of the flood in this channel this inconsistency can be explained by 1 a single 10 000 m 3 s 1 flood that caused at least 13 m of vertical incision in the channel hence enlarging the channel cross section 2 multiple floods of 10 000 m 3 s 1 or less each producing some incision of the channel or 3 an earlier flood of 40 000 m 3 s 1 creating the highest flood deposits and crossed drainage divides observed along crooked creek drainage followed by a later 10 000 m 3 s 1 flood associated with the most recent shorelines in alvord and coyote basins well developed shorelines of lake alvord at 1280 m and in coyote basin at 1278 m suggest that after the initial flood postflood overflow persisted for an extended period connecting alvord and coyote basins with the owyhee river of the columbia river drainage surficial weathering characteristics and planktonic freshwater diatoms in lake alvord sediment stratigraphically below mt st helens set sg tephra suggest deep open basin conditions at 13 14 ka 14 c yr and that the flood and prominent shorelines date to about this time but geomorphic and sedimentological evidence also show that alvord and coyote basins held older higher elevation lakes that may have released earlier floods down crooked creek

coordinated global radar observations of tidal and planetary waves in the mesosphere and lower thermosphere during january 20 30 1993 a multi instrument global campaign involving incoherent scatter medium frequency and meteor wind radars was conducted during the period of january 20 30 1993 to study the dynamics of the mesosphere and lower thermosphere data obtained from 15 radar stations covering a wide latitude range have been used to determine the global distribution of planetary and tidal waves during this 10 day campaign spectral analysis of the neutral winds measured by the radars in the altitude range from 80 to 130 km indicates the existence of a strong 48 hour wave near 90 km at latitudes between 40 n and 40 s that is present up to 108 km at 18 n the semidiurnal tide is large at middle and high latitudes near 90 km and is predominant above 110 km while the diurnal tide is observed to be particularly important in the upper mesosphere near 40 latitude a least squares fit to the radar data is performed to obtain the amplitudes and phases of the tidal and 48 hour waves comparison with national center for atmospheric research thermosphere ionosphere mesosphere general circulation model shows that the predictions from the model agree reasonably well with the observed global morphology of tidal wave amplitudes

megafloods and clovis cache at wenatchee washington immense late wisconsin floods from glacial lake missoula drowned the wenatchee reach of washington s columbia valley by different routes the earliest debacles nearly 19 000 cal yr bp raged 335 m deep down the columbia and built high pangborn bar at wenatchee as advancing ice blocked the northwest of columbia valley several giant floods descended moses coulee and backflooded up the columbia past wenatchee ice then blocked moses coulee and grand coulee to quincy basin became the westmost floodway from quincy basin many missoula floods backflowed 50 km upvalley to wenatchee 18 000 to 15 500 years ago receding ice dammed glacial lake columbia centuries more till it burst about 15 000 years ago after glacier peak ashfall about 13 600 years ago smaller great flood s swept down the columbia from glacial lake kootenay in british columbia the east wenatchee cache of huge fluted clovis points had been laid atop pangborn bar after the glacier peak ashfall then buried by loess clovis people came five and a half millennia after the early gigantic missoula floods two and a half millennia after the last small missoula flood and two millennia after the glacial lake columbia flood people likely saw outburst flood s from glacial lake kootenay

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

lunar tidal winds at adelaide and saskatoon at 80 to 100 km heights 1985 1990 winds data from the two sites were analyzed for lunar tides in 2 year groups the variation with height of the phase and amplitude of the tide showed considerable variability from year to year yet in general seasonal variations at particular heights were similar to those determined previously phases of the tide at the two sites were compared in order to estimate whether the tide was symmetric or antisymmetric for this purpose it was found necessary to use only 1 year data sets the predominance of symmetric tides during solstice months and antisymmetric tides at the equinox came as a surprise yet the result is in broad agreement with phase relations of the lunar geomagnetic tide

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

late quaternary megafloods from glacial lake atna southcentral alaska u s a abstract geomorphic stratigraphic geotechnical and biogeographic evidence indicate that failure of a pleistocene ice dam between 15 5 and 26 ka generated a megaflood from glacial lake atna down the matanuska valley while it has long been recognized that lake atna occupied 9000 km2 of south central alaska s copper river basin little attention has focused on the lake s discharge locations and behaviors digital elevation model and geomorphic analyses suggest that progressive lowering of the lake level by decanting over spillways exposed during glacial retreat led to sequential discharges down the matanuska susitna tok and copper river valleys lake atna s size 50 ka duration and sequential connection to four major drainages likely made it a regionally important late pleistocene freshwater refugium we estimate a catastrophic matanuska megaflood would have released 500 1400 km3 at a maximum rate of 3 106 m3 s 1 volumes for the other outlets ranged from 200 to 2600 km3 and estimated maximum discharges ranged from 0 8 to 11 3 106 m3 s 1 making lake atna a serial generator of some of the largest known freshwater megafloods

semidiurnal tidal climatology of the e region theoretical predictions of global monthly and seasonally averaged semidiurnal temperatures and winds between 80 and 150 km are presented and compared with seasonal means from measurements at the arecibo chatanika millstone hill and sondrestrom incoherent scatter radars the model values above 100 km are obtained by utilizing a set of tabulated hough mode extension functions to extrapolate the 2 2 2 3 2 4 and 2 5 propagating tidal modes at 100 km from a spectral model not valid in the e region due to the way molecular dissipation is parameterized to higher altitudes and by superimposing a component driven by in situ excitation important mainly above 140 km the monthly simulations demonstrate the close coupling that exists between seasonal and latitudinal structures and argue for an observational program emphasizing adequate seasonal and latitudinal coverage despite constraints imposed by the distributions of existing data with respect to month and year comparisons with the model reveal several trends that appear to be real 1 the model amplitudes are usually 20 50 smaller than those observed 2 vertical wavelengths are well predicted by the model but model phases generally lead the observations at middle and low latitudes by approximately 2 3 hours at all heights for both winds and temperatures 3 semidiurnal temperatures at middle and low latitudes in both the observations and model indicate significant seasonal changes in the phase of the temperature oscillation but not in the winds and 4 the seasonal trends in the model and observations are consistent with summer leading winter at millstone hill while the reverse is true at arecibo the sources of the absolute amplitude and phase discrepancies in the model which are probably connected with the adopted mean wind and thermal excitation specifications need to be investigated in addition a concerted effort must be made within the coupling energetics and dynamics of atmospheric regions cedar program to better delineate the seasonal latitudinal thermal structure and dynamics of the e region following the example of the extensive f region observational data base which has been accumulated over the last decade

high outflow channels on mars indicate hesperian recharge at low latitudes and the presence of canyon lakes abstract a number of martian outflow channels were carved by discharges from large dilational fault zones these channels were sourced by groundwater not surface water and when observed on high standing plateaus they provide indicators of elevated paleo groundwater levels we identify three outflow channels of hesperian age that issued from a 750 km long fault zone extending from candor chasma to ganges chasma two of these channels allegheny vallis and walla walla vallis have sources 2500 m above the topographic datum too high to be explained by discharge from a global aquifer that was recharged solely in the south polar region the indicated groundwater levels likely required regional sources of recharge at low latitudes the floodwaters that erupted from ophir cavus to form allegheny vallis encountered two ridges that restricted the flow forming temporary lakes the flow probably breached or overtopped these obstructions quickly catastrophically draining the lakes and carving several scablands after the last obstacle had been breached a single main channel formed that captured all subsequent flow we performed hydrologic analyses of this intermediate phase of the flooding prior to incision of the channel to its present depth using floodwater depths of 30 60 m we calculated flow velocities of 6 15 m s 1 and discharges in the range of 0 7 3 10 6 m 3 s 1 locally higher flow velocities and discharges likely occurred when the transient lakes were drained variable erosion at the channel and scabland crossing of mola pass 10644 suggests that the upper 25 30 m may consist of poorly consolidated surface materials underlain by more cohesive bedrock we infer that an ice covered lake with a surface elevation 2500 m probably existed in eastern candor chasma because this canyon is intersected by the ophir catenae fault system from which allegheny vallis and walla walla vallis originated we introduce a new hydrology concept for mars in which the groundwater system was augmented by recharge from canyon lakes that were formed when water was released by catastrophic melting of former ice sheets in tharsis by effusions of flood basalts this model could help to reconcile the expected presence of a thick cryosphere during the hesperian with the abundant evidence for groundwater as a source for some of the circum chryse outflow channels

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

atmospheric tide 2 the solar and lunar semidiurnal components solar and lunar semidiurnal wind and temperature oscillations from the surface to 400 km are simulated for average solar activity conditions utilizing the numerical tidal model described in part 1 hough mode decomposition of the solstitial solar semidiurnal tide excited by h2o and o3 insolation absorption below 80 km indicates that it is characterized by a predominance of 2 2 below 60 km about equal contributions of 2 2 2 3 and 2 4 between 70 and 90 km mostly 2 4 with some 2 5 and 2 2 between 90 and 120 km and a predominance of 2 2 above 140 km with secondary contributions from 2 3 and 2 5 the solstitial lunar semidiurnal tide is characterized by a predominance of 2 2 below 70 km 2 4 with secondary contributions from 2 2 2 3 and 2 5 between 80 and 110 km and by 2 2 with a fairly strong secondary contribution from 2 3 above 120 km similar descriptions for both the solar and lunar oscillations apply at equinox except that the asymmetric 2 3 and 2 5 modes are absent relative to the solar component lunar temperature and wind amplitudes are sufficiently large 20 in the lower and upper thermosphere to account for some of the observed variability previously attributed to the solar tide amplitudes of the 2 4 and 2 5 modes above 100 km are significantly affected by mesospheric eddy diffusion coefficients in excess of 2 106 cm s 1 the total solar semidiurnal exospheric temperature oscillation for average solar conditions ranges from 10 20 k poleward of 40 n to 40 60 k equatorward of 30 n and has its origin in three sources of excitation all of comparable importance 1 euv solar radiation absorption in the lower thermosphere 100 200 km 2 in situ momentum coupling due to the interaction of diurnal winds and diurnally varying ion drag and 3 tides propagating upwards from below 100 km in addition the calculations are compared with rocket meteor radar partial reflection thomson scatter and satellite data to evaluate the consistency of the model with observations

spatial and temporal dependence of temperature variations induced by atmospheric pressure variations in shallow underground cavities pressure induced temperature pit variations are systematically observed in the atmosphere of underground cavities such pit variations are due to the compressibility of the air damped by heat exchange with the rock surface it is important to characterize such processes for numerous applications such as the preservation of painted caves or the assessment of the long term stability of underground laboratories and underground waste repositories in this paper we thoroughly study the spatiotemporal dependence of the pit response versus frequency using vertical and horizontal profiles of temperature installed in an abandoned underground quarry located in vincennes near paris the pit response varies from about 20 10 3 c hpa 1 at a frequency of 2 10 4 hz to 2 3 10 3 c hpa 1 at a frequency of one cycle per day an analytical expression based on a simple heat exchange model accounts for the observed features of the pit response and allows for correcting the measured time series having standard deviations of about 10 2 c to residual variations with a standard deviation of about 2 10 3 c however a frequency dependent attenuation of the response corresponding to a reduction in amplitude with a factor varying from 2 to 3 is observed near the walls this effect is not included in the simple analytical expression but it can be accounted for by a one dimensional differential equation solved numerically where temperature variations in the atmosphere are damped by an effective radiative coupling with the rock surface complemented by a diffusive coupling near the walls the tip response is observed to remain stable over several years but a large transient enhancement of about a factor of two is observed near the roof at one location from july to october 2005 in a cavity located below the paris observatory an additional contribution is identified in the pit response function versus frequency for frequencies smaller than 2 10 5 hz this contribution can be described using a modified analytical expression that includes the effect of heat diffusion into the surrounding rock using this expression in this case also the temperature time series can then be corrected giving a residual standard deviation smaller than 1 6 10 3 c transient temporal variations of the pit response are observed in all sites with possible nonlinear components in the pit such effects are not properly understood at this stage and limit the reduction of time series to standard deviations of the order of 2 10 3 c and consequently limit the search for new transient or seasonal temperature signals for example due to the presence of tiny heat sources in the cavity or to geodynamical effects

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

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

glaciology ice sheet plumbing in antarctica it s not easy to work out what is going on beneath four kilometres of ice but remote imaging has enabled the discovery of the long distance discharge of water from one subglacial lake to another in antarctica

summary of pre 1980 tephra fall deposits erupted from mount st helens washington state usa mount st helens has been a prolific source of tephra fall deposits for about 40 000 years these tephra deposits 1 record numerous explosive eruptions 2 form important regional time stratigraphic marker beds and 3 record repeated changes in composition within and between eruptive periods

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

repeated sedimentation and exposure of glacial lake missoula sediments a lake level history at garden gulch montana usa abstract glaciolacustrine sediments record lake transgression regression and subaerial modification of the silty lake bottom of glacial lake missoula in the clark fork river valley the sequence preserved at garden gulch mt documents lake level fluctuations at 65 of its full pool volume twelve sedimentary cycles fine upwards from 1 very fine grained sandy silt to 2 silt with climbing ripples to 3 rhythmically laminated silt and some clay the cycles are fine grained turbidites capped locally by thin layers of angular gravel derived from local bedrock outcrops the gravels appear to be the toes of mass wasting lobes carried onto the exposed lakebed surface during repeated lake level lowerings periglacial wedges small rotational faults involutions and clastic dikes deform the tops of eleven cycles the wedges are 10 30 cm wide penetrate 30 70 cm deep are spaced the lowest five cycles are thicker and display more periglacial modification at their tops than the upper seven cycles the garden gulch section may represent as few as seven and as many as twelve substantial fillings and partial to complete drainings of glacial lake missoula

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

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

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

astoria fan sediments dsdp site 174 cascadia basin hf nd pb constraints on provenance and outburst flooding abstract the astoria submarine fan located off the coast of washington and oregon has grown throughout the pleistocene from continental input delivered by the columbia river drainage system enormous floods from the sudden release of glacial lake water occurred periodically during the pleistocene carrying vast amounts of sediment to the pacific ocean deep sea drilling project dsdp site 174 located on the southern distal edge of the astoria fan is composed of 879 m of terrigenous sediment the section is divided into two major units separated by a distinct seismic discontinuity an upper turbidite fan unit unit i and an underlying finer grained unit unit ii both units have overlapping ranges of nd and hf isotope compositions with the majority of samples having e nd values of 7 1 to 15 2 and e hf values 6 2 to 20 0 the most notable exception is the uppermost sample in the section which is identical to modern columbia river sediment nd depleted mantle model ages for the site range from 2 0 to 1 2 ga and are consistent with derivation from cratonic proterozoic source regions rather than cenozoic and mesozoic terranes proximal to the washington oregon coast the astoria fan sediments have significantly less radiogenic nd and hf isotopic compositions than present day columbia river sediment e nd 3 to 4 goldstein s j jacobsen s b 1987 nd and sr isotopic systematics of river water suspended material implications for crustal evolution earth planet sci lett 87 249 265 and suggest that outburst flooding tapping proterozoic source regions was the dominant sediment transport mechanism in the genesis and construction of the astoria fan pb isotopes form a highly linear 207 pb 204 pb 206 pb 204 pb array and indicate the sediments are a binary mixture of two disparate sources with isotopic compositions similar to proterozoic belt supergroup metasediments and columbia river basalts the combined major trace and isotopic data argue that outburst flooding was responsible for depositing the majority top 630 m of the sediment in the astoria fan