observation of coherent echoes with narrow spectra near 150 km altitude during daytime away from the dip equator 1 we present the rare observation of backscatter echoes perpendicular to the geomagnetic field from the 150 km altitude vicinity over a region situated away from the dip equator namely at gadanki 13 5 n 79 2 e 6 4 dip latitude a layer of weak echoes having signal to noise ratio snr of the order of 12 to 3 db was seen drifting downward from 157 km at 0930 lt to about 148 km at 1028 lt on july 12 1997 the doppler velocity as well as doppler width was in the range 10 20 ms 1 while there was no quasi periodicity as such in terms of echo occurrence the echo properties were in other respects very similar to 150 km echoes seen in equatorial regions this included the descending phase with time during the morning hours these constitute the first observations of daytime 150 km echoes away from the dip equator and only add to the mystery regarding the origin of these structures

jokulhlaup deposits in proglacial areas abstract this paper discusses the main causes and characteristics of jokulhlaup glacier burst floods and explores the extent to which they generate depositional landform and sediment assemblages that are distinct from those of normal braided river outwash type i outwash two main jokulhlaup outwash environments are identified type ii outwash produced by sudden drainage of ice dammed lakes and type iii associated with drainage during subglacial geothermal activity and distinguished by deposits resulting from high sediment concentrations and hyperconcentrated flows in fluid flows especially ones yielding type ii outwash the most common deposits are large scale expansion bars and locally eddy and pendant bars and mega ripples or dunes both forms normally composed of large scale gravel cobble cross bedding often capped by an imbricated boulder lag a type b2 lithofacies sequence the armour is absent only where runoff decreased too rapidly to allow surface winnowing other jokulhlaup facies include extensive boulder beds type c inverse normally graded cobble beds type ds ice proximal debris flow deposits and deformed bedding containing diamicton clasts types g and h and slack water sediments type a type iii outwash is dominated by massive homogeneous flood surge granules underlain by pre surge gravels and capped by post surge fluid bedforms reflecting deposition during both the rising and falling limbs of the flood hydrograph type e4 the paper demonstrates that jokulhlaups do generate distinctive assemblages of depositional landforms and sediments and concludes with a model of the dominant lithofacies sequences and associated landforms in proglacial environments subject to jokulhlaup drainage

a study on the low latitude daytime e region plasma irregularities using coordinated vhf radar rocket borne and ionosonde observations 1 in this paper we study the off electrojet low latitude daytime e region plasma irregularities using first multi instrument observations in india made during july 2004 by the mst radar from gadanki 13 5 n 79 2 e magnetic latitude 6 4 n langmuir probe on board the rh 300 mk ii rocket and ionosonde from sriharikota 13 6 n 80 2 e magnetic latitude 6 4 n radar echoes were confined to altitudes below 105 km and were observed in the form of a descending echoing layer with the descent rate of 1 km h virtual height of the e layer as observed by ionosonde shows identical descending behavior a detailed analysis based on the radar and ionosonde observations shows that the radar echoes are related to the range spread in the ionogram rocket observations made on 23 july 2004 revealed weak plasma irregularities with scale sizes more than 100 m and no noticeable irregularity at shorter scales the spectral slope of the irregularities observed by the rocket probe is found to be 4 for scales in between 1 km and 100 m during the rocket launch radar did not detect any echo conforming that the small scale irregularities were not present examination of concurrent observations of neutral wind made by timed doppler interferometry suggests that zonal wind plays a crucial role in forming electron density layers which become unstable via the gradient drift instability with background electric field or and zonal neutral wind generating low latitude e region plasma irregularities

tropical e region field aligned irregularities simultaneous observations of continuous and quasiperiodic echoes the antenna beam at 13 n off zenith direction of the indian mesosphere stratosphere troposphere mst radar at gadanki 13 5 n 79 2 e is orthogonal to geomagnetic field lines at 110 km altitude this beam was used to observe e region field aligned irregularities during july august 1994 february and june 1996 and july september 1997 with a range resolution of 600 m on a few occasions the radar was operated at 150 m range resolution also observations showed continuous and multiple echo regions during nighttime however out of the 15 nights of observations quasiperiodic qp echoes were also detected on the nights of july 20 21 1994 and september 3 4 1997 in this paper major features of these quasiperiodic echoes in the form of height time maps of echo intensity are presented on july 20 21 1994 quasiperiodic echoes with a periodicity of about 2 4 min from the altitude between 102 and 116 km appeared as tilted striations in the height time intensity maps the rate of descent of altitude associated with these tilted striations was in the range of 40 60 m s 1 the fluctuations in the doppler velocity along the length of striations resembled a wave structure with vertical wavelength of the order of 18 20 km observations on september 3 4 1997 suggest that these high frequency waves initially modulate the es layer up to an altitude as high as 120 km and produce the quasiperiodic variation in the echoes as time progresses the period of qp echoes as well as the echo expanse decreases and finally the normal continuous layer emerges

a geologically constrained monte carlo approach to modeling exposure ages from profiles of cosmogenic nuclides an example from lees ferry arizona we present a user friendly and versatile monte carlo simulator for modeling profiles of in situ terrestrial cosmogenic nuclides tcns our program available online at http geochronology earthsciences dal ca downloads models html permits the incorporation of site specific geologic knowledge to calculate most probable values for exposure age erosion rate and inherited nuclide concentration while providing a rigorous treatment of their uncertainties the simulator is demonstrated with 10be data from a fluvial terrace at lees ferry arizona interpreted constraints on erosion based on local soil properties and terrace morphology yield a most probable exposure age and inheritance of 83 9 14 1 19 1 ka and 9 49 2 52 1 21 104 atoms g 1 respectively 2 without the ability to apply some constraint to either erosion rate or age shallow depth profiles of any cosmogenic nuclide except for nuclides produced via thermal and epithermal neutron capture e g 36cl cannot be optimized to resolve either parameter contrasting simulations of 10be data from both sand and pebble sized clasts within the same deposit indicate grain size can significantly affect the ability to model ages with tcn depth profiles and when possible sand not pebbles should be used for depth profile exposure dating

simulation of snow shielding corrections for cosmogenic nuclide surface exposure studies abstract snow cover reduces cosmogenic nuclide production rates in bedrock corrections for snow cover can be more than 10 in mountainous mid latitude regions where many glacial chronologies have been constructed using cosmogenic nuclide surface dating of landforms most published snow corrections use historic climate data of limited duration that are not likely to reflect adequately the full range of snow conditions over the time of exposure we present a model for describing the impact of snow burial on long term exposure histories of landforms the model applies an energy balance approach to snowpack evolution and incorporates both historic and long term climate proxy data attenuation of cosmogenic fast neutrons is modeled alternatively as a simple exponential decrease with increased shielding or as a thin surface layer with constant production followed by an exponential decrease with increasing depth the choice of attenuation model has little effect on the modeled results for the cairngorms but will have a more significant effect in regions characterized by thinner less dense snowpacks spatial variability in snow cover is modeled as a function of elevation only ignoring local variability in snow accumulation as a result of slope aspect wind redistribution and local topography thus model results reveal general spatial and temporal trends in snow shielding effects rather than site specific corrections applications to data from the cairngorm mountains of scotland show that the constant plus exponential cpe production rate depth profile reduces but does not eliminate snow shielding effects under present day conditions snow at 900 m in the cairngorm mountains reduces average production rates by 6 using the cpe profile and 9 with the exponential profile ep long term climate simulations from 15 5 ka through today produce larger snow shielding effects mainly because they predict an increased proportion of precipitation as snowfall during the younger dryas at 900 m this long term simulation reduces average cosmogenic isotope production rates by 12 cpe and 14 ep these results indicate that snow shielding corrections based on historic climate records may be a potential source of systematic error in midlatitude mountainous regions

progressive incision of the channeled scablands by outburst floods the surfaces of earth and mars contain large bedrock canyons that were carved by catastrophic outburst floods reconstructing the magnitude of these canyon forming floods is essential for understanding the ways in which floods modify planetary surfaces the hydrology of early mars and abrupt changes in climate flood discharges are often estimated by assuming that the floods filled the canyons to their brims with water however an alternative hypothesis is that canyon morphology adjusts during incision such that bed shear stresses exceed the threshold for erosion by a small amount here we show that accounting for erosion thresholds during canyon incision results in near constant discharges that are five to ten fold smaller than full to the brim estimates for moses coulee a canyon in the channeled scablands which was carved during the pleistocene by the catastrophic missoula floods in eastern washington usa the predicted discharges are consistent with flow depth indicators from gravel bars within the canyon in contrast under the assumption that floods filled canyons to their brims a large and monotonic increase in flood discharge is predicted as the canyon was progressively incised which is at odds with the discharges expected for floods originating from glacial lake outbursts these findings suggest that flood carved landscapes in fractured rock might evolve to a threshold state for bedrock erosion thus implying much lower flood discharges than previously thought

high resolution observations of 150 km echoes at jicamarca high resolution soundings of equatorial upper e region echoes at jicamarca exhibit gravity wave modulated signal intensity distributions and doppler velocities corresponding to vertical plasma drifts a gravity wave wind driven interchange instability is suggested as a possible generation mechanism of the field aligned plasma irregularities responsible for the echoes the echoes may be utilized in gravity wave studies and in zonal electric field measurements by radars with modest sensitivities

late pleistocene seismites from lake issyk kul the tien shan range kyrghyzstan abstract the aim of the study is to record the occurrence of sediment deformation structures in one of the tectonically most active areas on the globe the tien shan range in central asia and to examine the significance of the deformations as indicators of palaeoseismicity soft sediment deformation structures in form of balls and pseudo nodules are exposed in the issyk kul basin within interfingering beds of shallow lacustrine beach and fluviatile origin additional deformation structures that were encountered are a complex and chaotic folded structure giant balls and a pillar structure which has not been previously reported where marl intrudes down into coarse pebbley sand and forms pillar morphology liquefaction features and bedforms related to storm and breaking waves were not encountered neither was there evidence of turbidites seven field criteria for relating soft sediment deformation to palaeoseismic triggering provide strong evidence for a seismic origin of the deformation structures empirical relationships between magnitude and the maximum distance from an epicenter to liquefaction sites make the active epicentral zone north of lake issyk kul with its frequent high magnitude events the most favorable source for the deformation structures luminescence dating of the sediments gives a time window of 26 2 1 to 10 5 0 7 ka bp indicating latest pleistocene seismic activity

structural and lithological controls on large quaternary rock avalanches sturzstroms in arid northwestern argentina landsat thematic mapper tm analysis aerial photograph interpretation and field studies of the semiarid puna plateau adjacent eastern cordillera and sierras pampeanas of argentina lat 24 28 s have revealed the existence of at least 55 rock avalanche deposits with volumes larger than 10 6 m 3 that formed by the collapse of entire mountain fronts the spatial distribution of landslide deposits is not random but it clusters along mountain fronts bounded by active faults inspection in the field reveals five principal controls on the distribution of these events the source area of the rock avalanches has two topographic constraints 1 vertical relief contrasts between the breakaway zone and the mountain front must exceed a threshold of 400 m and 2 the slope inclinations must be steeper than 20 rock avalanches are restricted to three types of lithology granites low grade metamorphic rocks and coarse clastic sediments structural controls are very important rock avalanches are controlled by planar structures such as bedding planes exfoliation joints minor faults and cleavage that all dip toward the valley in addition major slide clusters occur along mountain fronts that underwent quaternary reverse fault reactivation of former transfer faults with strike slip kinematics the trigger mechanism for the majority of these landslides is interpreted to be seismic although the ages of some major slides are about 30 ka and they may correspond to a more humid interval in southern south america

impact of middle pleistocene saalian glacial lake outburst floods on the meltwater drainage pathways in northern central europe insights from 2d numerical flood simulation abstract the terrestrial margins of the middle pleistocene ice sheets in northern central europe were characterised by the formation of extensive ice dammed lakes which were controlled by the blockage of spillways by the ice margin the largest ice dammed lake had a volume of 224 km and formed in a late stage of the first saalian ice advance mis 6 in central germany the failure of the ice dam in the bedrock outlet channel triggered a major glacial lake outburst flood flood related erosional and depositional features include large scale scours trench like channels streamlined hills giant bars and run up deposits indicating a wide spreading of the outburst flood in an early stage and the incision of trench like valleys in a later stage the incision of large valleys in the proximal flood pathway strongly impacted the regional drainage system by providing an efficient drainage network the trench like channels initiated by the lake outburst flood became a crucial part of the ice marginal drainage and subsequent fluvial system the reconstructed outlet hydrographs imply peak discharges of 465 000 673 000 m s 1 the numerical simulation indicates flow depths of up to 87 m flow velocities of up to 7 ms 1 peaks of the bed shear stress of 2500 nm 2 and the inundation of large parts of northwestern germany and the northern netherlands the numerical simulation of the outburst flood was conducted on both the modern digital elevation model and on palaeotopographic models representing the palaeotopography prior to the outburst flood and during maximum flood related incision respectively distally the outburst flood probably followed an east west trending route through northwestern germany and the central netherlands into the ice dammed lake in the southern north sea basin the added water volume might have led to the overspill and drainage of the proglacial lakes in the central netherlands and the north sea lake in a chain reaction eventually opening an east west trending meltwater drainage pathway along the southwestern margin of the decaying ice sheet

lower e region field aligned irregularities studied using the equatorial atmosphere radar and meteor radar in indonesia 1 this paper presents the first observations of lower e region echoes made with the equatorial atmosphere radar ear located in west sumatra indonesia 0 2 s 100 32 e dip latitude 10 36 s the lower e region echoes observed over west sumatra display descending layer structures with occasional descent to altitude as low as 85 km the descending characteristics resemble the characteristics of tidal winds simultaneous observations of wind measured using a meteor radar show tidal wind fields with westward and northward winds above and eastward and southward winds below the velocities of the field aligned irregularities fai observed by the ear are found to agree quite well with the winds measured by the meteor radar this suggests that in the collision dominated lower e region the fai velocities represent essentially the neutral winds the observations of low altitude fai are found to be consistent with the gradient drift instability except those occurring below 90 km which deserves further investigation

first vhf radar observations of tropical latitude e region field aligned irregularities indian mst radar at gadanki 13 5 n 79 2 e 12 5 dip was operated during july august 1994 to observe the 3 m scale size field aligned irregularities associated with the lower e region irregularity structure was studied by using height time variation of the echo intensity and weighted mean doppler velocity in this paper results of three diurnal cycles of observation are presented field perpendicular echoes were observed both during daytime and nighttime a layered irregularity structure extending down to altitude below 86 km was seen during the nighttime the daytime structure showed a narrow echoing region with significant downward slope doppler velocity was in the range of 20 50 ms 1 both during day and night and was in general consistent with the slope of scattering structure observed in the height time intensity plots

the holocene paleolimnology of lake issyk kul kyrgyzstan trace element and stable isotope composition of ostracodes the stable isotope and trace element geochemistry of ostracode shells from lake issyk kul kyrgyzstan provide an important new paleoclimate record for central asia the n 18 o n 13 c sr ca mg ca and u ca composition of shells from the species candona neglecta found in two piston cores constrains the paleohydrology of the lake from 8700 to 1000 calendar yr before present these data combined with robust chronologies based on 16 ams 14 c dates suggest that the region went from a relatively moist climate in the early holocene to a more arid climate in the late holocene intense freshwater input presumably glacial runoff flowed into the lake from 8700 to 8300 cal yr bp as evident from the n 18 o and n 13 c values from 8300 to 6900 cal yr bp n 18 o and sr ca values indicate that the lake was relatively fresh and an open basin and u ca values suggest that the lake was well mixed with well oxygenated bottom waters there is a transition zone between 6900 and 4900 cal yr bp when n 18 o and sr ca values rapidly increase and mg ca and u ca values rapidly decrease during this period the lake evolved from an open freshwater well mixed lake to a closed more saline less well mixed lake for the remainder of the record n 18 o sr ca mg ca and u ca are relatively constant implying conditions similar to modern conditions although the slight increasing trend in sr ca may suggest an increase in salinity over this period the n 13 c values were approximately in equilibrium with atmospheric co2 in the early part of the record but became relatively negative in the later part of the record this indicates that the dominant mechanism controlling the isotopic composition of dissolved inorganic carbon shifted from exchange with the atmosphere to variations in biological productivity fl 2001 elsevier science b v all rights reserved

paleohydraulic reconstruction of flash flood peaks from boulder deposits in the colorado front range nine watersheds in the colorado front range with steep bedrock channels were used to test the accuracy of paleohydraulic reconstruction of large flash floods using boulder deposits the nine basins consist of eight small ungauged basins ranging in size from 1 6 to 29 km2 and the big thompson river at the mouth of the big thompson canyon draining 790 km2 between 1923 and 1976 all nine basins had had one catastrophic flash flood the magnitude of which has been estimated by the conventional slope area method in each basin coarse boulder deposits of the large flash floods were identified and three axes of the five largest boulders were measured along with at least two profiles of the valley cross section a simple arithmetic average of two theoretical and two empirical relationships was used to estimate average flood velocity using boulder size and shape average depth was estimated as the arithmetic average of four values computed from the manning equation a regression equation for boulder size and unit stream power a relative smoothness equation and a modified shields relationship the appropriate flood width for the estimated average depth was found by iteration using the valley cross sections the paleohydraulic discharges thus computed generally underestimate conventional slope area discharge estimates on small streams by as much as 75 although the average amount is only 28 too low and the reconstructed discharge in one stream was 31 too large the big thompson river flood of 1976 was overestimated by 76 reasons for discrepancy in reconstructed peaks could include 1 the possibility that floods may have been able to move boulders larger than those available to be moved 2 overestimation of the slope area discharge because high water marks were set prior to erosion of the channel 3 underestimation of original roughness coefficients and 4 macroturbulent effects during fast deep flows the paleohydraulic technique is applied to two other streams in colorado with sedimentological evidence of large flash floods but no conventional indirect discharge estimates a small tributary to the big thompson river draining 1 8 km2 has a paleohydraulic reconstructed flood peak of about 60 m3 s from a flood in 1976 using boulders excavated from a foundation site in holocene alluvium along boulder creek in boulder colorado a paleohydraulic reconstructed flood peak of between 860 and 1 512 m3 s is calculated this is 1 4 to 2 4 times the magnitude of the estimated 500 yr flood

morphology and seasonal characteristics of low latitude e region quasiperiodic echoes studied using large database of gadanki radar observations 1 in this paper we study the morphology seasonal features and statistics of low latitude quasiperiodic qp echoes using an unprecedented data set of 147 nights of observations spanning over all seasons made using the gadanki radar the qp echoes have periods 2 20 min and occur on more than 50 nights they are often found embedded in descending echoing layers whose characteristics resemble to those of tidal winds their occurrence shows strong seasonal dependence with 48 of the time in summer 26 32 in equinox and 14 in winter the qp echoes have a tendency to appear first during 21 00 lt which could last for 2 8 h leading to their maximum occurrence rate during postmidnight hours height time occurrences of radar echoes and qp structures both show common descending behavior which agree extremely well with the observed descending behavior of the es layers we also find that the seasonal variations of qp echo occurrence are in very close agreement with that of the es activity tidal activity in the same height region and also gravity wave activity in the mesosphere interestingly the occurrence statistics are much more than their midlatitude counterpart and time of first appearance time of maximum occurrence and duration of qp echoes all strongly contrast the midlatitude features these observations have been discussed in detail in the light of current understanding of qp echoes

morphological response to quaternary deformation at an intermontane basin piedmont the northern tien shan kyrghyzstan abstract the tien shan is a most active intracontinental mountain building range with abundant quaternary fault related folding in order to improve our understanding of quaternary intermontane basin deformation we investigated the intermontane issyk kul lake area an anticline that was up warped through the piedmont cover causing partitioning of the alluvial fan veneer to follow the morphological scenario during the warping process we relied on surface exposed and trenched structures and on alluvial fans and bajadas as reference surfaces we used air photos and satellite images to analyze the spatial temporal morphological record and determined the age of near surface sediments by luminescence dating we demonstrate that the up warped ak teke hills are a thrust generated subdued anticline with strong morphological asymmetry which results from the coupling of the competing processes of up warp and erosional feedback the active creeks across the up warped anticline indicate that the antecedent drainage system kept pace with the rate of uplift the rivers which once sourced the piedmont like the toru aygyr kultor and the dyuresu became deeply entrenched and gradually transformed the study area into an abandoned morphological surface the up warp caused local lateral drainage diversion in front of the northern backlimb and triggered the formation of a dendritic drainage pattern upfan luminescence dating suggest that the period of up warp and antecedent entrenchment started after 157 ka the morphologically mature study area demonstrates the response of fluvial systems to growing folds on piedmont areas induced by a propagating frontal fold at a thrust belt edge following shortening

enhanced velocities and a shear in daytime esq over kwajalein and their relationship to 150 km echoes over the dip equator we present the first evidence of enhanced irregularity drift velocities and a velocity shear in the daytime e region at 4 3 n dip latitude these features found in radar measurements from kwajalein during q type sporadic e esq events are interpreted in terms of a polarization electric field that develops in response to the presence of latitudinal gradients in field line integrated conductivity caused by sporadic e layers because the e region over kwajalein connects directly to 150 km altitude over the magnetic dip equator we suggest that a similar polarization process is responsible for the so called 150 km echoes that have been observed routinely by the jicamarca radar

inherited strike slip faults as an origin for basement cored uplifts example of the kungey and zailiskey ranges northern tian shan 1 basement cored uplifts bounded by steeply dipping reverse faults are mechanically difficult to explain reactivation of strike slip faults that aid the formation of new high angle reverse faults in the surrounding crust may provide one origin for these structures this hypothesis is explored by examining the late miocene to quaternary evolution of the kungey and zailiskey ranges in the northern tian shan these ranges are cored by the kemin chilik fault kcf an inherited paleozoic structure with sinistral separation of basement terranes range growth in response to northward propagation of the tian shan has taken place along a network of steeply dipping reverse and oblique slip faults surrounding the kcf deformation of a low relief unconformity separating neogene strata from paleozoic basement records structural growth in response to fault slip deformed river terraces surrounding the ranges are correlated to a well preserved chronosequence in the southern kungey range cosmogenic10be dating of this chronosequence combined with offset measurements yields slip rates ranging from 0 07 to 0 37 mm yr for dip slip faults and 1 1 to 1 5 mm yr for strike slip faults late quaternary activity in the kungey zailiskey ranges is consistent with the longer term outward stepping pattern of range growth based on cross sections constrained from the folded unconformity surface deformed neogene strata and quaternary terraces faults building the kungey range are inferred to steepen at depth and emanate from a shear zone co located with the reactivated kcf this geometry is consistent with a slip partitioned system developed by an obliquely slipping reactivated fault at depth

gps velocity field for the tien shan and surrounding regions 1 measurements at 400 campaign style gps points and another 14 continuously recording stations in central asia define variations in their velocities both along and across the kyrgyz and neighboring parts of tien shan they show that at the longitude of kyrgyzstan the tarim basin converges with eurasia at 20 2 mm yr nearly two thirds of the total convergence rate between india and eurasia at this longitude this high rate suggests that the tien shan has grown into a major mountain range only late in the evolution of the india eurasia collision most of the convergence between tarim and eurasia within the upper crust of the tien shan presumably occurs by slip on faults on the edges of and within the belt but 1 3 mm yr of convergence is absorbed farther north at the dzungarian alatau and at a lower rate with the kazakh platform to the west the tarim basin is thrust beneath the tien shan at 4 7 mm yr with respect to eurasia the ferghana valley rotates counterclockwise at 0 7 myr 1 about an axis at the southwest end of the valley thus gps data place a bound of 4 mm yr on the rate of crustal shortening across the chatkal and neighboring ranges on the northwest margin of the ferghana valley and they limit the present day slip rate on the right lateral talas ferghana fault to less than 2 mm yr gps measurements corroborate geologic evidence indicating that the northern margin of the pamir overthrusts the alay valley and require a rate of at least 10 and possibly 15 mm yr

kilometric irregularities in the e and f regions of the daytime equatorial ionosphere observed by a high resolution hf radar during the international equatorial electrojet year high resolution vertical hf coherent radar experiments were performed in the ivory coast 9 24 62 n 5 37 38 w at frequencies in the range 1 8 mhz kilometric scale irregularities were observed in the e and f regions of the daytime equatorial ionosphere these irregularities constitute a large sporadic e layer within the altitude range 100 to 150 km larger than the width of the equatorial electrojet the higher part of this irregular region is detached in the morning and evening forming an intermediate region at 150 160 km these 150 km echoes overtakes the e region electrojet echoes at 100 120 km at noon the echolocation shows that the reflections arise from the vertical direction up to 150 km with a significant contribution of reflections from east west directions above 110 km the f1 region irregularities are characterized by time and height scales significantly larger than the e region irregularities scales as in the e region the f1 region reflections arise from the vertical and from east west directions when the reflection distance increases the variations of the doppler frequency versus the observation distance at several sounding frequencies are well explained by a horizontal motion of the irregular plasma flow both in the e and f regions with velocities of 100 m s and 130 m s respectively

late glacial lakes in the thompson basin british columbia paleogeography and evolution during the decay of the cordilleran ice sheet 10 000 13 000 bp glacial lakes developed within valleys that dissect the interior plateau of british columbia in this paper we 1 illustrate a procedure for assessing paleo water planes that has general application 2 document lake paleogeography and evolution in the thompson valley 3 provide new data on the glacio isostatic response of the central cordillera and 4 present new evidence of its late glacial environment we employ geomorphology and sedimentology digital elevation models and new technologies differential global positioning systems ground penetrating radar and geographic information systems to refine paleogeographic reconstructions of glacial lakes glacial lake thompson and glacial lake deadman were ribbon shaped width to length ratio 3 100 deep 140 to 50 m lakes that contained significant water volumes 84 24 km3 they lengthened to the west and their water level lowered as ice decayed final ice dam failure resulte

first results on low latitude e and f region irregularities obtained using the gadanki ionospheric radar interferometer a 30 mhz radar has recently been established at gadanki 13 5 n 79 2 e 6 5 n magnetic latitude to make unattended observations of the ionospheric field aligned irregularities fai this radar called the gadanki ionospheric radar interferometer giri has been designed to have scanning capability of 100 in the east west plane perpendicular to earth s magnetic field and interferometry imaging system to study drifts and spatial distribution of plasma irregularities at both large and small scales in this paper we present the first results on the e and f region fai made using the scanning capability of the giri daytime observations of e region fai show type 2 echoes with velocities predominantly upward northward downward southward at altitudes 100 km 100 km and westward eastward in the forenoon afternoon with signature of tidal wind field f region irregularities show bottom type bottomside and plume structures with close resemblance to those observed over the magnetic equator observations made with the east west scanning capability have been used to study the origin evolution and drift of the fai for the first time from gadanki eastward drifts are estimated to be 90 210 m s 1 during 20 24 lt upward velocity as large as 500 m s 1 has been observed in the initial phase of the plume structures intriguingly downward velocity as large as 60 m s 1 has also been observed in the plumes displaying descending pattern observed in the early evening hours these results are presented and discussed in the light of current understanding of low latitude plasma irregularities and future prospects of giri are outlined

giant landslides topography and erosion abstract distributions of slope angles in tectonically active mountain belts point to the development of threshold conditions where hillslopes attain a critical inclination or height at which they fail readily because of limitations in material strength it has been proposed that hillslopes adjust to rapid uplift and bedrock incision through an increase in the rate of relief limiting landsliding rather than gradual slope steepening here we test this concept by investigating the relationship between mean local relief h which we take to be a proxy of long term erosion rates e and the occurrence of over 300 of the largest v 10 8 m 3 terrestrial landslides on earth we find that nearly two thirds of these giant landslides have occurred in the steepest 5 of the earth s land surface where relief is close to its proposed upper strength limit they are primarily located in deeply incised valleys along fault bounded fringes of active mountain belts and in volcanic arcs this distribution coincides with areas of high long term erosion rates 4 mm yr 1 confirming that giant landslides contribute to rapid denudation of mountains most of the eroded volume is concentrated in the smallest but steepest parts of mountain belts and volcanic arcs first order estimates of minimum erosion rates accomplished by the largest landslides are 0 01 mm yr 1 these rates are between 1 and 10 of the late pleistocene to holocene mean erosion rates in a given area importantly the landslide erosion rates show a nonlinear increase with mean local relief suggesting that the contribution of giant landslides in total and per event increases significantly with increasing overall erosion rates however giant landslides also occur in areas of lower than average relief h 300 700 m irrespective of whether threshold hillslopes have developed or not factors contributing to these failures include soft rocks extensive low angle discontinuities high rates of fluvial bedrock incision and tectonically driven deformation and slope loading

late pleistocene holocene rise and collapse of lake suguta northern kenya rift abstract the late pleistocene to middle holocene african humid period ahp was characterized by dramatic hydrologic fluctuations in the tropics a better knowledge of the timing spatial extent and magnitude of these hydrological fluctuations is essential to decipher the climate forcing mechanisms that controlled them the suguta valley 2 n northern kenya rift has recorded extreme environmental changes during the ahp extensive outcrops of lacustrine sediments ubiquitous wave cut notches shorelines and broad terrace treads along the valley margins are the vestiges of lake suguta which once filled an 80 km long and 20 km wide volcano tectonic depression lake suguta was deep between 16 5 and 8 5 cal ka bp during its maximum highstand it attained a water depth of ca 300 m a surface area of ca 2150 km2 and a volume of ca 390 km3 the spatial distribution of lake sediments the elevation of palaeo shorelines and other geomorphic evidences suggest that palaeo lake suguta had an overflow towards the turkana basin to the north after 8 5 cal ka bp lake suguta abruptly disappeared a comparison of the lake suguta water level curve with other reconstructed water levels from the northern part of the east african rift system shows that local insolation which is dominated by precessional cycles may have controlled the timing of lake highstands in this region our data show that changes of lake levels close to the equator seem to be driven by fluctuations of spring insolation while fluctuations north of the equator are apparently related to variations in summer insolation however since these inferred timings of lake level changes are mostly based on the radiocarbon dating of carbonate shells which may have been affected by a local age reservoir alternative dating methods are needed to support this regional synthesis between 12 7 and 11 8 cal ka bp approximately during the northern hemisphere high latitude younger dryas the water level of lake suguta fell by ca 50 m suggesting that remote influences also affected local hydrology

investigation on the occurrence of mid latitude e region irregularity by wuhan vhf radar and its relationship with sporadic e layer by using the 2015 2016 data set of newly built wuhan very high frequency vhf radar we investigate the occurrence of e region field aligned irregularities fais in mid latitude china region for the first time wuhan e region fais present the strongest occurrence of quasi periodic qp echoes at postsunset period in the height range of 100 120 km and moderate occurrence of continuous echoes at postsunrise period in the height range of 90 100 km characteristics including temporal and altitudinal distribution doppler spectra and period of qp echoes are presented from a statistical point of view we find that e region fais observed by wuhan vhf radar show strong linkage with the concurrent sporadic e layer observed by ionosonde in general doppler spectra present type 2 feature with velocity in the range of 50 m s and width less than 50 m s our results also indicate that mid latitude e region fais are closely associated with es layer several mechanisms were proposed to interpret the mid latitude e region fais however further investigation is required to understand the generation with different ionospheric background and irregularity types

radiocarbon dating of minute gastropods and new constraints on the timing of late quaternary spring discharge deposits in southern arizona usa abstract gastropod shells are commonly preserved in quaternary sediments but are often avoided for radiocarbon dating because some taxa incorporate 14 c deficient carbon during shell formation recently brennan and quade 1997 quat res 47 329 336 found that some minute taxa vallonia pupilla and succineidae appear to yield reliable 14 c ages for late pleistocene samples a more rigorous evaluation of the 14 c inventory of minute gastropods is presented here which involved measuring the 14 c activity of specimens collected live in two geologic settings that maximize the potential for ingestion of old carbon 1 alluvium dominated by paleozoic carbonate rocks and 2 adjacent to extant springs with highly 14 c deficient water present at the surface we found that several minute taxa including vallonia incorporate significant and variable amounts of old carbon 2 to 30 during shell formation the 14 c activities of the land snails pupilla blandi and euconulus fulvus however are indistinguishable from the 14 c activity of live plants the 14 c activity of the semi aquatic gastropod catinella sp family succineidae deviates from modern values in the presence of 14 c deficient water by an amount equivalent to 10 of the local carbon reservoir effect these results imply that at least some minute gastropods can provide reliable 14 c ages even when 14 c deficient carbon is readily available to demonstrate an application of our findings we 14 c dated shells from p muscorum e fulvus and succinea sp family succineidae recovered from the coro marl a late pleistocene spring fed marsh deposit exposed at the murray springs paleoindian site in the san pedro valley of southern arizona usa radiocarbon ages obtained from the minute gastropods show that the unit was deposited between 25 000 and 13 000 14 c years ago the marl is situated 15 m above the modern water table at murray springs and is similarly positioned in discontinuous outcrops along a 150 km stretch of the san pedro valley thus the 14 c ages of minute gastropods presented here may be used to infer the timing of high water table levels throughout the valley

late quaternary intensified monsoon phases control landscape evolution in the northwest himalaya the intensity of the asian summer monsoon circulation varies over decadal to millennial time scales and is reflected in changes in surface processes terrestrial environments and marine sedi ment records however the mechanisms of long lived 2 5 k y intensified monsoon phases the related changes in precipitation distribution and their effect on landscape evolution and sedimen tation rates are not yet well understood the arid high elevation sectors of the orogen correspond to a climatically sensitive zone that currently receives rain only during abnormal i e strength ened monsoon seasons analogous to present day rainfall anom alies enhanced precipitation during an intensified monsoon phase is expected to have penetrated far into these geomorphic threshold regions where hillslopes are close to the angle of failure we as sociate landslide triggering during intensified monsoon phases with enhanced precipitation discharge and sediment flux leading to an increase in pore water pressure lateral scouring of rivers and ov ersteepening of hillslopes eventually resulting in failure of slopes and exceptionally large mass movements here we use lacustrine deposits related to spatially and temporally clustered large land slides 0 5 km 3 in the sutlej valley region of the northwest him alaya to calculate sedimentation rates and to infer rainfall patterns during late pleistocene 29 24 ka and holocene 10 4 ka inten sified monsoon phases compared to present day sediment flux measurements a fivefold increase in sediment transport rates re corded by sediments in landslide dammed lakes characterized these episodes of high climatic variability these changes thus em phasize the pronounced imprint of millennial scale climate change on surface processes and landscape evolution

mid latitude e region field aligned irregularities observed with the mu radar fine structures e region field aligned irregularities were observed on june 24 25 1989 with the mu radar at shigaraki japan 34 9 n 136 1 e geomagnetic latitude 25 0 n the 3 2 m scale irregularities were observed with the mu radar in five main beam directions each of which was nearly perpendicular to the geomagnetic field at 100 km altitude doppler spectra were obtained every 20 s with a range resolution of 600 m field perpendicular echoes appeared from 2130 to 2330 lt and from 0400 to 1100 lt times that correspond to postsunset and postsunrise period in the e region a preliminary examination of the doppler spectra indicates spectral widths of 50 120 m s 1 and the mean doppler velocities are well below the ion acoustic speed these spectral characteristics are consistent with those obtained in the equatorial and auroral electrojets and have been attributed to the gradient drift instability the echoes observed during the postsunset and postsunrise periods showed quite different morphologies in the time height distribution for this reason they are classified into two types continuous and quasi periodic the appearance of the continuous echoes was mainly continuous in time and situated between 90 and 100 km altitude during the postsunrise period the appearance of the quasi periodic echoes was intermittent with periods of 5 10 min and situated above 100 km altitude during the postsunset period the quasi periodic echoes showed phase propagation toward the radar while the averaged mean doppler velocity was away from the radar by measuring the time delays in echo regions from five directions an apparent westward motion approximately 120 m s 1 of the irregularity regions was estimated

displacement along the red river fault constrained by extension estimates and plate reconstructions significant e w extension and or compression must have been generated by displacements along the red river fault rrf since its curvature does not match a small circle centered at the euler pole for the indochina south china plate pair the amount of extension perpendicular to the rrf offshore vietnam depends on the magnitude of left lateral displacement along the rrf in general the larger the left lateral displacement along the fault the smaller the amount of e w extension all purely strike slip models of the opening of the south china sea that assume large displacements 250 km along the rrf encounter major problems because they imply little extension or even considerable shortening offshore east vietnam this is inconsistent with the presence of large elongated basins offshore vietnam using a plate tectonic model we compare continental extension values implied by different magnitudes of displacement along the rrf with crustal stretching estimates derived from 2 d profiles modeled from gravity data we utilize 2 d gravity forward models to restore the extended continental margin crust to its original position prior to extension we find that substantial amounts of extension for offshore vietnam can only be modeled assuming moderate displacements along the rrf compatible with the presence of a southward subducting proto south china sea the total amount of ene wsw extension offshore northern vietnam constrained by our 2 d gravity profiles and gravity inversion increases southward from 36 to 89 km along the yinggehai basin these values of ene wsw extension are consistent with 250 km of left lateral displacement along the rrf

methods for predicting peak discharge of floods caused by failure of natural and constructed earthen dams floods from failures of natural and constructed dams constitute a widespread hazard to people and property expeditious means of assessing flood hazards are necessary particularly in the case of natural dams which may form suddenly and unexpectedly we revise statistical relations derived from data for past constructed and natural dam failures between peak discharge qp and water volume released v0 or drop in lake level d but assert that such relations even when cast into a dimensionless form are of limited utility because they fail to portray the effect of breach formation rate we then analyze a simple physically based model of dam breach formation to show that the hydrograph at the breach depends primarily on a dimensionless parameter kv0 gl 2d7 2 where k is the mean erosion rate of the breach and g is acceleration due to gravity the functional relationship between qp and takes asymptotically distinct forms depending on whether 1 relatively slow breach formation or small lake volume or 1 relatively fast breach formation or large lake volume theoretical predictions agree well with data from dam failures for which k and thus can be estimated the theory thus provides a rapid means of predicting the plausible range of values of peak discharge at the breach in an earthen dam as long as the impounded water volume and the water depth at the dam face can be estimated

late quaternary glaciation in the kyrgyz tien shan the tien shan of kyrgyzstan contains multiple moraines and drift from late quaternary glaciations the spatial temporal distribution of the glaciers inferred from the moraines suggests that the main factor controlling glacier advance here was the availability of moisture the dominant modern climatic signatures in northern central asia include orographic thunderstorms in summer cold and dry siberian high pressure cells in winter and westerly cyclonic storms from the north atlantic and eastern mediterranean in spring and fall changes in any of these systems during the late quaternary would have varied precipitation delivery to and glacier growth in the kyrgyz tien shan geomorphic mapping and reconnaissance level 10be cosmic ray exposure dating of moraine sequences in six drainages indicate that there were multiple maximum advances of similar extents and equilibrium line depressions across the range glaciers in the north and east of the kyrgyz tien shan last advanced to their maximum positions during marine oxygen isotope stage mis 5 and again during mis 4 while in the south and west of the range advance occurred during mis 3 in contrast to maritime europe and north america there is no evidence of a major glacial advance during mis 2 glacier advances during mis 2 and since were restricted to the vicinity of modern glaciers allowing the older glacial record to be preserved well