geophysical surveys of a pluvial lake barrier deposit beatty junction death valley california usa abstract we used ground penetrating radar gpr and seismic refraction to image the internal stratigraphy of a beach barrier deposit at beatty junction northern death valley to better understand its depositional environment in the context of variations in the level of the former lake manly the deposit is a gravelly bar 500 m long with 4 m of surface relief that formed at a shoreline of lake manly during the end of the last pleistocene ice age the gpr profiles provide subsurface images that we interpret as progradational foreset beachface strata in the uppermost 2 m and the surface of an earlier bar at depths of 2 to 6 m we conclude that the crest of the bar migrated in a landward direction during the construction of the uppermost 4 m of the bar as lake level rose the seismic survey indicates a sharp velocity increase from 760 m s to 1510 m s at the base of the bar which we interpret as the boundary between well sorted gravelly beach deposits and underlying older fan deposits the depth of the base of the bar varies between 5 m and 10 m the elevation of the bar is comparable to that of other shoreline features in death valley that formed during the mis 6 5e 186 120 ka highstand measurements of fault slip on the nearby northern death valley fault have documented only strike slip motion in absence of any evidence for significant vertical uplift in the area during the late pleistocene and holocene we conclude that the bar probably formed during mis 6 5e this conclusion is subject to uncertainty due to discrepancies in age dates reported for the deposit

coarse clastic barrier environments evolution and implications for quaternary sea level interpretation abstract this paper reviews recent work particularly from eastern canada on the dynamics and evolution of coarse clastic barriers it is argued that an understanding of quaternary coastal changes on paraglacial glacially influenced coasts can only be achieved with a knowledge of gravel barrier morphodynamics and sedimentation gravel barriers are distinctive coastal forms in which morphological inheritance and sediment sorting provide major behavioral controls spatially adjacent gravel barriers may display different depositional tendencies prograde seawards migrate landward or aggrade vertically such inconsistent spatial behaviour must be considered in terms of an erosional front advancing landward under stationary or rising sea level redistribution of sediment across or along the erosional front supplies sediment for the development of gravel barriers which in turn provides environments for fine grained deposition which is favourable for further barrier migration an example of an erosional front is given from chezzetcook inlet nova scotia three stages are recognized in the development of gravel barriers starting with the initiation of small drift aligned forms at the leading edge of the erosional front as sea level rises this is followed by a period of consolidation and stabilization when drift aligned forms may become swash aligned conditions for this transition are discussed under rising sea levels it is difficult to explain the conditions leading to the formation of multiple parallel swash aligned ridges although three hypotheses are advanced all of which may operate in different locations the third stage is associated with the breakdown of barriers as sediment supply fails and or sea level rises drift aligned forms are inherently unstable and show signs of pre breakdown stress in the form of reworking and remobilization of proximal sediments into cells swash aligned barriers may be breached revert to drift alignment become segmented or be overstepped some gravel is re incoporated in barriers farther landward while other material is passed seaward of the erosional front and becomes abandoned on the shoreface gravel barriers may exert a major influence on estuary and back barrier environments especially where they control the depositional record the implications for the reconstruction and interpretation of quaternary environments are summarized

constraints on mantle viscosity and laurentide ice sheet evolution from pluvial paleolake shorelines in the western united states abstract the deformation pattern of the paleoshorelines of extinct lake bonneville were among the first features to indicate that earth s interior responds viscoelastically to changes in surface loads gilbert 1885 here we revisit and extend this classic study of isostatic rebound with updated lake chronologies for lake bonneville and lake lahontan as well as revised elevation datasets of shoreline features the first order domal pattern in the shoreline elevations can be explained by rebound associated with the removal of the lake load we employ an iterative scheme to calculate the viscoelastic lake rebound which accounts for the deformation of the solid earth and gravity field to calculate a lake load that is consistent with the load deformed paleotopography we find that the domal deformation requires a regional earth structure that exhibits a thin elastic thickness of the lithosphere 15 25 km and low sublithospheric maxwell viscosity 10 19 pa s after correcting for rebound due to the lake load shoreline feature elevations reveal a statistically significant northward dipping trend we attribute this trend to continent scale deformation caused by the ice peripheral bulge of the laurentide ice sheet and take advantage of the position of these lakes on the distal flank of the peripheral bulge to provide new insights on mantle viscosity and laurentide ice sheet reconstructions we perform ice loading calculations to quantify the deformation of the solid earth gravity field and rotation axis that is caused by the growth and demise of the laurentide ice sheet we test three different ice reconstructions paired with a suite of viscosity profiles and confirm that the revealed trend can be explained by deformation associated with the laurentide ice sheet when low viscosities below the asthenosphere are adopted we obtain best fits to shoreline data using ice models that do not have the majority of ice in the eastern sectors of the laurentide ice sheet with the caveat that this result can be affected by lateral variations in viscosity we show that pluvial lakes in the western united states can place valuable constraints on the laurentide ice sheet the shape of its peripheral bulge and the underlying mantle viscosity

late quaternary chronology of tufa deposits walker lake nevada walker lake a terminal desertic lake in mineral county nevada has fluctuated greatly in lake level throughout its long history due to changes in climate and drainage in its late pleistocene high stand walker lake formed the southernmost embayment of pluvial lake lahontan calcareous tufa and other shoreline deposits of pleistocene and holocene ages provide a valuable record of past lake levels studies of tufa morphology and stable isotope character closely integrated with sedimentologic data show great promise for elucidating the post glacial climatic history of the great basin three prominent shoreline carbonate deposits below 1250 m have been studied in the field and with stable isotope and radiocarbon analyses the oldest deposit 18 000 radiocarbon yrs b p consists of massive bowl shaped tufa heads outcropping from conspicuous wavecut and fan deltaic terraces three bigheads are covered by alluvial fan deposits which in turn are coated by an encrusting tufa of 3 cm average thickness

carbonate deposition pyramid lake subbasin nevada 2 lake levels and polar jet stream positions reconstructed from radiocarbon ages and elevations of carbonates tufas deposited in the lahontan basin most of the tufas in the pyramid lake subbasin were deposited within the last 35 000 yr including most of the mound tufas that border the existing lake many of the older tufas 21 000 yr b p contained in the mounds were formed in association with ground water discharge the radiocarbon 14c ages of the older tufas represent maximum estimates of the time of their formation lake lahontan experienced large and abrupt rises in level at 22 000 15 000 and 11 000 yr b p and three abrupt recessions in level at 16 000 13 600 and 10 000 yr b p the lake level rises that were initiated at 23 500 and 15 500 yr b p are believed to indicate the passage of the polar jet stream over the lahontan basin during expansion of the laurentide ice sheet the jet stream moved south across the basin and during the contraction of the ice sheet the jet stream moved north across the basin the bulk of the carbonate contained in the mound tufas was deposited during the last major lake cycle 23 500 12 000 yr b p indicating that ground and surface water discharges increased at 23 500 and decreased at 12 000 yr b p a lake level oscillation that occurred between 11 000 and 10 000 yr b p is represented by a 2 cm thick layer of dense laminated tufa that occurs at and below 1180 m in the low elevation tufa mounds and at 1205 m in the winnemucca lake subbasin

viscosity structure of the crust and upper mantle in western nevada from isostatic rebound patterns of the late pleistocene lake lahontan high shoreline received 13 july 2005 revised 26 october 2006 accepted 31 january 2007 published 8 june 2007 1 large lakes can both produce and record significant crustal deformation we present an analysis of the isostatic rebound pattern recorded in the shorelines of paleolake lahontan in western nevada using a layered maxwell viscoelastic model the inferred viscosity structure depends on loading history we use three variants of a well documented lake surface elevation model as input and recover corresponding estimates of viscosity and density structure a simple two layer model with an elastic plate over an inviscid half space fits the observed elevation pattern quite well with a residual variance of 32 of the data variance using multilayered finite viscosity models the residual variance is reduced to 20 of the data variance which is very near to the noise level in the higher resolution models the viscosity is below 10 18 pa s over the depth range from 80 to 160 km the minimum viscosity is very similar to the value that has been seen in the eastern great basin from similar analyses of lake bonneville shorelines but the lowviscosity zone is thinner beneath bonneville making small adjustments to a seismically derived density structure allows an improved fit to the shoreline observations additionally we find that small variations in proposed loading models can result in presumably spurious density inversions and suggest that this modeling approach provides a test for loading histories

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

rise and fall of late pleistocene pluvial lakes in response to reduced evaporation and precipitation evidence from lake surprise california widespread late pleistocene lake systems of the basin and range province indicate substantially greater moisture availability during glacial periods relative to modern times but the climatic factors that drive changes in lake levels are poorly constrained to better constrain these climatic forcing factors we present a new lacustrine paleoclimate record and precipitation estimates for lake surprise a closed basin lake in northeastern california we combine a detailed analysis of lake hydrography and constitutive relationships describing the water balance to determine the influence of precipitation evaporation temperature and seasonal insolation on past lake levels at its maximum extent during the last deglaciation lake surprise covered 1366 km 2 36 of the terminally draining surprise valley watershed using paired radiocarbon and 230 th u analyses we dated shoreline tufa deposits from wave cut lake terraces in surprise valley california to determine the hydrography of the most recent lake cycle this new lake hydrograph places the highest lake level 176 m above the present day playa at 15 19 0 18 calibrated ka 14 c age this significantly postdates the last glacial maximum lgm when lake surprise stood at only moderate levels 65 99 m above modern playa similar to nearby lake lahontan to evaluate the climatic factors associated with lake level changes we use an oxygen isotope mass balance model combined with an analysis of predictions from the paleoclimate model intercomparison project 3 pmip3 climate model ensemble our isotope mass balance model predicts minimal precipitation increases of only 2 18 during the lgm relative to modern compared to an 75 increase in precipitation during the 15 19 ka highstand lgm pmip3 climate model simulations corroborate these findings simulating an average precipitation increase of only 6 5 relative to modern accompanied by a 28 decrease in total evaporation driven by a 7 c decrease in mean annual temperature lgm pmip3 climate model simulations also suggest a seasonal decoupling of runoff and precipitation with peak runoff shifting to the late spring early summer from the late winter early spring our coupled analyses suggest that moderate lake levels during the lgm were a result of reduced evaporation driven by reduced summer insolation and temperatures not by increased precipitation reduced evaporation primed basin and range lake systems particularly smaller isolated basins such as surprise valley to respond rapidly to increased precipitation during late heinrich stadial 1 hs1 post lgm highstands were potentially driven by increased rainfall during hs1 brought by latitudinally extensive and strengthened midlatitude westerly storm tracks the effects of which are recorded in the region9s lacustrine and glacial records these results suggest that seasonal insolation and reduced temperatures have been underinvestigated as long term drivers of moisture availability in the western united states

late holocene hydroclimate inferences for the northern great basin from little lake elko county nevada usa abstract prominent lunette dunes 500 800 m long 50 80 m wide and up to 5 m tall are present on the floor of the independence valley in northeast nevada usa these dunes border the downwind margins of circular playas at the end of a drainage descending from the east humboldt mountains which terminates in an ephemeral water body named little lake gastropod shells from the little lake playa yield radiocarbon ages of 400 cal yr bp after correction for a hard water effect a similar age was obtained for shells from the crest of one of the lunettes deeper sediment in this lunette yielded shell ages clustering around 600 cal yr bp this pattern suggests two intervals of relatively persistent water at little lake both of which ended with lake desiccation and deflation of sediment and shells to the adjacent lunette shells from the crest of another lunette yielded radiocarbon ages between 3800 and 1750 cal yr bp this dune therefore is considerably older and accumulated over a much longer stretch of time using the global surface water explorer years between 1984 and 2018 were identified in which little lake contained water in most of the available summer imagery these years form three clusters 1984 1987 1997 2000 and 2017 2018 snow water equivalent swe is greater in the mountains snow makes up a greater percent of total annual precipitation and palmer drought severity index is more positive in this region in years when water is present in little lake compared with those in which the lake remains dry values of the pdo are also higher in years when little lake holds water although the hydrology of little lake may be influenced to an unknown degree by upstream water diversions this overall pattern implies that the lake and its associated lunettes are a sensitive recorder of late holocene hydroclimate variability in the northern great basin

tidal correction of topex poseidon altimetry for seasonal sea surface elevation and current determination off the pacific coast of canada altimetry from the topex poseidon satellite is analyzed for the waters off british columbia canada tides are removed using harmonic constants from two coastal and two global models and the accuracy of this detiding is assessed by using these same models and one digital filter to remove the tide from the time series of three representative coastal tide gauges it is demonstrated that inaccurate m2 s2 and k1 tide removal from topex poseidon altimetry can introduce systematic biases to the calculation of seasonally averaged fields average summer and winter sea surface heights are calculated from the detided altimetry and estimates of their accuracy nearshore are computed using concurrent time series from 11 tide gauges finally these seasonal elevations are blended with those from the 11 tide gauges and the associated surface currents are calculated using a diagnostic finite element model these currents are compared with those calculated from historical conductivity and temperature versus depth measurements and those measured by historical near surface current meters

a great basin wide dry episode during the first half of the mystery interval the existence of the big dry event from 14 9 to 13 8 14 c kyrs in the lake estancia new mexico record suggests that the deglacial mystery interval 14 5 12 4 14 c kyrs has two distinct hydrologic parts in the western usa during the first great basin lake estancia shrank in size and during the second great basin lake lahontan reached its largest size it is tempting to postulate that the transition between these two parts of the mystery interval were triggered by the ird event recorded off portugal at about 13 8 14 c kyrs which post dates heinrich event 1 by about 1 5 kyrs this twofold division is consistent with the record from hulu cave china in which the initiation of the weak monsoon event occurs in the middle of the mystery interval at 16 1 kyrs i e about 13 8 14 c kyrs

carbonate deposition pyramid lake subbasin nevada 1 sequence of formation and elevational distribution of carbonate deposits tufas abstract during the late quarternary the elevation of terrace cutting and carbonate deposition in the pyramid lake subbasin were controlled by constancy of lake level imposed by spill to adjoining subbasins sill elevations are 1177 1183 m mud lake slough sill 1207 m emerson pass sill and 1265 m darwin pass sill carbonate deposition was favored by 1 hydrologic closure 2 proximity to a source of calcium 3 elevated water temperature and 4 a solid substrate the thickness and aspect of tufa are a function oflake level dynamics relatively thin sheets and pendant sheets were deposited during a rising or falling lake the upper parts of thick reef form tufas have a horizontal aspect and were deposited in a lake which was stabilized by spill to the carson desert subbasin the lower parts of the reef form tufas are thinner and their outer surface has a vertical aspect indicating that the lower part formed in a receding lake the thickest and most complete sequences of tufa are mounds that border the pyramid lake shore the tops of the tallest mounds reach the elevation of the darwin pass sill and many mounds have been eroded to the elevations of the mud lake slough sill of the emerson pass sill the sequence of tufa formation from oldest to youngest displayed in these mounds is 1 a beachrock containing carbonate cemented volcanic cobbles 2 broken and eroded old spheroids that contain thinolitic tufa and an outer rind of dense laminated tufa 3 large cylindrical tubular tufas capped by 4 coatings of old dense tufas and 5 several generations of old branching tufa commonly associated with thin platy tufas and coatings of thinolitic tufa 6 young spheroids that contain poorly oriented young thinolitic tufa in the center and several generations of radially oriented young thinolitic tufas near the outer edge 7 a transitional thinolite to branching tufa 8 two or more layers of young branching tufa 9 a 0 5 cm thick layer of fine grained dolomite 10 a 2 cm thick layer of young dense laminated tufa 11 a 0 1 cm thick layer of encrusting tufa that was covered by a beach deposit and 12 a 1 0 cm thick layer of porous encrusting tufa that coated the beach deposit and the sides of tufa mounds the elevational ranges of the principal varieties of tufa are not related to terrace or spill elevations it seems likely that the distribution of tufa varieties is related to variation in the thermal structure or chemistry of lake lahontan it is hypothesized that the thinolitic tufa ikaite formed in the near freezing hypolimnion and the braching tufa calcite formed in the seasonally warmer epiliminion of the lake

factors affecting 14c ages of lacustrine carbonates timing and duration of the last highstand lake in the lahontan basin abstract two processes contribute to inaccurate 14c age estimates of carbonates precipitated within the lahontan basin nevadacalifornia low initial 14c c ratios in lake water reservoir effect and addition of modern carbon to calcium carbonate after its precipitation the mast reliable set of 14c ages on carbonates from elevations 1310 m in the pyramid and walker lake subbasins indicate that lakes in all seven lahontan subbasins coalesced 14 200 14c yr b p forming lake lahontan lake lahontan achieved its 1330 m highstand elevation by 13 800 14 c yr b p and receded to 1310 m by 13 700 14c yr b p calculations based on measured carbonate accumulation rates of the amount of time lake lahontan exceeded 1310 and 1330 m 500 and 50 yr are consistent with this chronology the timing of the lake lahontan highstand is of interest because of the linkage of highstand climates with proximity to the polar jet stream the brevity of the lahontan highstand is interpreted to indicate that the core of the southern branch of the polar jet stream remained only briefly over the lahontan basin

latest pleistocene history of pluvial lake franklin northeastern nevada usa at its maximum extent during the last glacial cycle lake franklin covered 1100 km 2 of the ruby valley of northeastern nevada making it one of the largest pluvial lakes between lakes bonneville and lahontan mapping of shorelines surveying of topographic profiles and radiocarbon dating of gastropod shells were employed to reconstruct the latest pleistocene history of the lake during the first half of the last glacial maximum lgm lake franklin covered 42 of its maximum area this extent increased to 60 during the second half of the lgm some radiocarbon ages suggest that the lake briefly rose to near its highstand between 20 and 18 ka but the best constrained rise occurred ca 17 ka when the lake rapidly transgressed to its highstand elevation of 1850 m this rise was synchronous with highstands of nearby pluvial lakes implicating a regional shift in the balance between precipitation and potential evaporation the lake dropped to 1843 m before rising once more to 1850 m ca 16 0 ka after falling and stabilizing at 1843 m again ca 15 4 ka the lake rapidly regressed to 70 by 14 8 ka this regression was synchronous with the fall of lake bonneville from the provo shoreline and the regression of lake lahontan from the sehoo shoreline radiocarbon ages and stratigraphic evidence document a final transgression in the latest pleistocene that reached 1820 m 34 of maximum area ca 13 0 ka synchronous with the recess peak glaciation in the sierra nevada and overlapping with the start of the younger dryas and minor transgressions of lakes bonneville lahontan and owens the correspondence of this lake franklin history with other climate archives from this region underscores the value of pluvial lake deposits as sources of paleoclimate information and indicates synchronous forcing of climate changes during the last glacial interglacial transition

vertical deformation of lacustrine shorelines along breached relay ramps catlow valley fault southeastern oregon usa abstract vertical deformation of pluvial lacustrine shorelines is attributed to slip along the catlow valley fault a segmented basin and range style normal fault in southeastern oregon usa the inner edges of shorelines are mapped along three breached relay ramps along the fault to examine the effect of fault linkage on the distribution of slip shoreline inner edges act as paleohorizontal datums so deviations in elevation from horizontal outside of a 2 m error window are taken to be indications of fault slip the sites chosen represent a spectrum of linkage scenarios in that the throw on the linking fault compared to that on the main fault adjacent to the linking fault varies from site to site results show that the maturity of the linkage between segments i e larger throw on the linking fault with respect to the main fault does not control the spatial distribution of shoreline deformation patterns of shoreline deformation indicate that the outboard linking and or smaller ramp faults have slipped since the shorelines formed observations indicate that displacement has not fully localized on the linking faults following complete linkage between segments

late pleistocene glaciations in the northwestern sierra nevada california pleistocene fluvial landforms and riparian ecosystems in central california responded to climate changes in the sierra nevada yet the glacial history of the western sierra remains largely unknown three glacial stages in the northwestern sierra nevada are documented by field mapping and cosmogenic radionuclide surface exposure crse ages two crse ages of erratic boulders on an isolated till above bear valley provide a limiting minimum age of 76 400 3800 10be yr another boulder age provides a limiting minimum age of 48 800 3200 10be yr for a broad crested moraine ridge within bear valley three crse ages producing an average age of 18 600 1180 yr were drawn from two boulders near a sharp crested bouldery lateral moraine that represents an extensive tioga glaciation in bear valley nine crse ages from striated bedrock along a steep valley transect average 14 100 1500 yr and suggest rapid late glacial ice retreat from lower fordyce canyon with no subsequent extensive glaciations these ages are generally consistent with glacial and pluvial records in east central california and nevada

numerical dating of a late quaternary spit shoreline complex at the northern end of silver lake playa mojave desert california a comparison of the applicability of radiocarbon luminescence terrestrial cosmogenic nuclide electron spin resonance u series and amino acid racemization methods a late quaternary spit shoreline complex on the northern shore of pleistocene lake mojave of southeastern california usa was studied with the goal of comparing accelerator mass spectrometry ams radiocarbon luminescence electron spin resonance esr terrestrial cosmogenic radionuclide tcn surface exposure amino acid racemization aar and u series dating methods the pattern of ages obtained by the different methods illustrates the complexity of processes acting in the lakeshore environment and highlights the utility of a multi method approach tcn surface exposure ages mostly 20 30 ka record the initial erosion of shoreline benches whereas radiocarbon ages on shells determined in this and previous studies within the spit supported by aar data record its construction at fluctuating lake levels from 16 to 10 ka luminescence ages on spit sediment 6 7 ka and esr ages on spit shells 4 ka are anomalously young relative to radiocarbon ages of shells within the same deposits the significance of the surprisingly young luminescence ages is not clear the younger esr ages could be a consequence of post mortem enrichment of u in the shells high concentrations of detrital thorium in tufa coating spit gravels inhibited the use of single sample u series dating detailed comparisons such as this provide one of the few means of assessing the accuracy of quaternary dating techniques more such comparisons are needed

late pleistocene to present lake level fluctuations at pyramid and winnemucca lakes nevada usa a new lake level curve for pyramid and winnemucca lakes nevada is presented that indicates that after the 15 500 cal yr bp lake lahontan high stand 1338 m lake level fell to an elevation below 1200 m before rising to 1230 m at the 12 000 cal yr bp younger dryas high stand lake level then fell to 1155 m by 10 500 cal yr bp followed by a rise to 1200 m around 8000 cal yr bp during the mid holocene levels were relatively low 1155 m before rising to moderate levels 1190 1195 m during the neopluvial period 4800 3400 cal yr bp lake level again plunged to about 1155 m during the late holocene dry period 2800 1900 cal yr bp before rising to about 1190 m by 1200 cal yr bp levels have since fluctuated within the elevation range of about 1170 1182 m except for the last 100 yr of managed river discharge when they dropped to as low as 1153 m late holocene lake level changes correspond to volume changes between 25 and 55 km 3 and surface area changes between 450 and 900 km 2 these lake state changes probably encompass the hydrologic variability possible under current climate boundary conditions

shoreline processes and the age of the lake lahontan highstand in the jessup embayment nevada the well developed shoreline record of pluvial lake lahontan in the jessup embayment nevada is used to refine the history of late pleistocene lake level fluctuations and to assess controls on shoreline development and distribution controls on the strength and type of shorelines developed include local slope the amount and characteristics of sediment available for transport the availability of accommodation space and length of time the lake level resides at a particular shoreline elevation at the sehoo highstand and during the early part of the regression strong storm winds and waves from the south southeast set up a clockwise net shore drift pattern near the head of the embayment although significant differences in local slope geometry of the shoreline and wave energy existed in the embayment crestal heights of constructional shoreline features formed at the highstand vary 2 6 m in elevation and hence provide a relatively precise marker of the highstand elevation radiocarbon dating of a camel bone preserved in high shoreline deposits indicates that the lake reached its highest elevation of 1338 5 m in the embayment and receded from that elevation immediately prior to 13 070 60 yr b p similar and slightly older radiocarbon ages on gastropod shells preserved in barrier deposits at 1327 m 13 280 110 yr b p and 1331 m 13 110 110 yr b p suggest that the final rise to the highstand was very rapid and that the lake maintained its highest stand for a very brief period of time perhaps only for years or decades the brevity of the highstand is reasonable in light of the recent formation of similar barrier features in modern pyramid lake which formed in less than seven months due to a rapid increase in lake level

interactions of earthquakes in central italy over the past 100 yr through coulomb stress changes and implications for seismic hazardsinteractions of earthquakes in central italy over the past 100 yr through coulomb stress changes and implications for seismic hazards

timing of the last glaciation and subsequent deglaciation in the ruby mountains great basin usa abstract the timing of the last pleistocene glaciation in western north america is becoming increasingly well understood largely due to improved methods of obtaining numerical ages of glacial deposits and landforms among these cosmogenic radionuclide surface exposure dating has been widely applied to moraines of mountain glaciers providing the framework for understanding terrestrial climate change during and since the last glaciation in western north america during the late pleistocene the great basin of the western united states hosted numerous mountain glaciers the deposits of which can provide valuable records of past climate changes if their ages can be precisely determined in this study twenty nine cosmogenic radionuclide 10be surface exposure ages from a suite of moraines in seitz canyon western ruby mountains limit the timing of the last glacial episode in the interior great basin known as the angel lake glaciation results indicate that deposition of a terminal moraine and two recessional moraines began just prior to 20 5 ka and continued until 20 0 ka retreat from the next younger recessional moraine began at 17 2 ka and final deglaciation began at 14 8 ka these ages are broadly consistent with cosmogenic surface exposure ages from the eastern sierra nevada and the western wasatch mountains in the western and eastern extremes of the great basin respectively furthermore these ages suggest that the valley glacier in seitz canyon was at or near its maximum extent before and during the hydrologic maxima of pleistocene lakes in the great basin supporting previous suggestions that a cool and wet climate persisted in this region during the early part of the last glacial interglacial transition

environmental history of southern patagonia unravelled by the seismic stratigraphy of laguna potrok aike laguna potrok aike located in southernmost patagonia argentina 52s is a 100 m deep hydrologically closed lake that probably provides the only continental southern patagonian archive covering a long and continuous interval of several glacial to interglacial cycles in the context of the planned international continental scientific drilling program initiative potrok aike maar lake sediment archive drilling project several seismic site surveys that characterize in detail the sedimentary subsurface of the lake have been undertaken long sediment cores recovered the material to date and calibrate these seismic data laguna potrok aike is rimmed steeply circular in shape with a diameter of 3ae5 km and is surrounded by a series of subaerial palaeoshorelines reflecting varying lake level highstands and lowstands seismic data indicate a basinwide erosional unconformity that occurs consistently on the shoulder of the lake down to a depth of 33 m below 2003 ad lake level marking the lowest lake level during late glacial to holocene times cores that penetrate this unconformity comprise marine isotope stage 3 dated sediments 45 kyr bp 3ae5 m below and post 6800 cal yr bp transgressional sediments above the unconformity this middle holocene transgression following an unprecedented lake level lowstand marks the onset of a stepwise change in moisture as shown by a series of up to 11 buried palaeoshorelines that were formed during lake level stillstands at depths between 30 and 12 m two series of regressive shorelines between 5800 to 5400 and 4700 to 4000 cal yr bp interrupt the overall transgressional trend in the basin mound like drift sediments occur after 6000 cal yr bp documenting the onset of lake currents triggered by a latitudinal shift or an increase in wind intensity of the southern hemispheric westerlies over laguna potrok aike at that time furthermore several well defined lateral slides can be recognized the majority of these slides occurred during the mid holocene lake level lowering when the slopes became rapidly sediment charged because of erosion from the exposed shoulder sediments around 7800 and 4900 cal yr bp several slides went down simultaneously probably triggered by seismic shaking

valleys paleolakes and possible shorelines at the libya montes isidis boundary implications for the hydrologic evolution of mars abstract we describe the results of our morphologic stratigraphic and mineralogic investigations of fluvial landforms paleolakes and possible shoreline morphologies at the libya montes isidis planitia boundary the landforms are indicative of aqueous activity and standing bodies of water including lakes seas and oceans that are attributed to a complex hydrologic cycle that may have once existed on mars in the noachian 3 7 ga and perhaps also in the hesperian 3 1 ga our observations of the libya montes isidis planitia boundary between 85 86 5 e and 1 8 5 n suggest that 1 the termination of valley networks between roughly 2500 and 2800 m coincide with lake size ponding in basins within the libya montes 2 an alluvial fan and a possible delta layered morphologies and associated al phyllosilicates identified within bright polygonally fractured material at the front of the delta deposits are interpreted to be the results of fluvial activity and discharge into a paleolake 3 the arabia shoreline appears as a series of possible coastal cliffs at about 3600 and 3700 m indicating two distinct still stands and wave cut action of a paleosea that temporarily filled the isidis basin the early hesperian and 4 the deuteronilus shoreline appears at 3800 m and is interpreted to be a result of the proposed sublimation residue of a frozen sea that might have filled the isidis basin similar to the vastitas borealis formation vbf identified in the northern lowlands we interpret the morphologic geologic setting and associated mineral assemblages of the libya montes isidis planitia boundary as results of fluvial activity lake size standing bodies of water and an environmental change over time toward decreasing water availability and a cold and dry climate

paleoshoreline geomorphology of boon tsagaan nuur tsagaan nuur and orog nuur the valley of lakes mongolia abstract we conducted a preliminary study of paleoshoreline features associated with boon tsagaan nuur tsagaan nuur and orog nuur lakes located in the gobi altai transition zone of the valley of lakes dolina ozor which stretches from central to western mongolia the paleoshoreline features were first identified on radarsat satellite sar imagery we investigated the features during the 1998 field season of the joint mongolian russian american archaeological expedition to the gobi altai region we identified paleoshorelines of multiple elevations in the field which are considered to be relict beach ridges and wave cut terraces other paleolake landforms include spits and gilbert type deltas these landforms are complex large and well established implying that the paleolakes were stable for extended periods the reconstructed paleolakes cover extensive areas of the valley floor implying that hydrological and climatic conditions were very different in the past paleolake expansions may have occurred under a variety of circumstances one hypothesis is that the high lake stands occurred during the wetter period corresponding to the oxygen isotope stage 3 prior to the last glacial maximum lgm during the warmest early holocene and the late holocene or during all these periods if low evaporation rates due to lower temperatures glacier meltwater and possibly increased precipitation are important factors then the expansions may have occurred during the terminal late glacial period after the last glacial maximum the greatly expanded lakes in the gobi altai could have significantly affected the quaternary human demography and migration in the region

complex exposure histories of chert clasts in the late pleistocene shorelines of lake lisan southern israel activities of 26 al and 10 be in five chert clasts sampled from two beach ridges of late pleistocene lake lisan precursor of the dead sea in southern israel indicate low rates of chert bedrock erosion and complex exposure burial and by inference transport histories the chert clasts were derived from the senonian mishash formation a chert bearing chalk which is widely exposed in the nahal zin drainage basin the drainage system that supplied most of the material to the beach ridges simple exposure ages assuming only exposure at the beach ridge sampling sites range from 35 to 354 ky using the ratio 26 al 10 be total clast histories range from 0 46 to 4 3 my unrelated to the clasts current position and exposure period on the late pleistocene beach ridges 160 177 m below sea level optically stimulated luminescence dating of fine sediments from the same and nearby beach ridges yielded ages of 20 0 s 1 4 ka and 36 1 s 3 3 ka these ages are supported by the degree of soil development on the beach ridges and correspond well with previously determined ages of lake lisan which suggest that the lake reached its highest stand around 27 000 cal years bp if the clasts were exposed only once and than buried beyond the range of significant cosmogenic nuclide production then the minimum initial exposure and the total burial times before delivery to the beach ridge are in the ranges 50 1300 ky and 390 3130 ky respectively alternatively the initial cosmogenic dosing could have occurred during steady erosion of the source bedrock back calculating such rates of rock erosion suggests values between 0 4 and 12 m my 1 t he relatively long burial periods indicate extended sediment storage as colluvium on slopes and or as alluvial deposits in river terraces some clasts may have been stored for long periods in abandoned pliocene and early pleistocene routes of nahal zin to the mediterranean before being transported again back into the nahal zin drainage system and washed on to the shores of lake lisan during the late pleistocene copyright 2003 john wiley sons ltd

combining radiocarbon and cosmogenic ages to constrain the timing of the last glacial interglacial transition in the uinta mountains utah usa twenty lake sediment cores extracted upstream from last glacial maximum terminal moraines constrain the timing of the glacial interglacial transition in the uinta mountains utah usa the stratigraphy observed in the cores and accelerator mass spectrometry 14 c dating of inorganic silty clay beneath gyttja temporally constrain local deglaciation the majority of basal ages fall within the bolling allerod interval with strong overlap at ca 12 7 cal calibrated kyr b p this convergence matches regional evidence of rising temperatures increasing aridity falling pluvial lake levels and glacial retreat near the end of the last glacial interglacial transition normalized estimates of glacier terminus retreat and elevation rise in the uinta mountains and elsewhere in the rocky mountains derived from consideration of cosmogenic ages on terminal moraines consistently average 10 k y between ca 20 and 13 ka implying a regionally uniform climate forcing during deglaciation minor variations between these rates likely reflect hypsometric effects during deglaciation seven lakes dammed by cirque floor moraines have basal ages within or slightly younger than the younger dryas interval suggesting advances of favorably located cirque glaciers before the glacial interglacial transition was complete

a 25 000 year record of earthquakes on the owens valley fault near lone pine california implications for recurrence intervals slip rates and segmentation models seven trenches in eastern california across the owens valley fault near lone pine expose two episodes of faulting since early holocene time in the form of 1 m throw in lacustrine beds with liquefaction that were buried and then faulted again 1 m by the m 7 5 to 7 75 a d 1872 owens valley earthquake geomorphic maps applications of sequence stratigraphy and analyses of radiocarbon from charcoal and tufa deposits indicate that the paleoearthquake the penultimate event here occurred between 10 200 200 and 8800 200 cal yr b p the cumulative vertical displacement from these last two earthquakes in three trenches averages 2 4 0 3 m 2 and the penultimate event has slightly larger displacements a synthesis of available data indicates that the antepenultimate event was probably as large and occurred between ca 24 000 and 14 000 cal yr b p 2 thus the two interseismic intervals between the last three surface faulting earthquakes on the southern owens valley fault are each 10 000 yr this 25 000 year record indicates that the two event normal oblique slip rate on the owens valley fault near lone pine is 1 0 0 5 m k y this result is similar to that of several previous geological studies here yet it is still slower than slip rates on the northern owens valley fault and several factors slower than contemporary geodetic measurements this study attempts to account for different dating methods and interpretational uncertainties to acknowledge how little is known about the slip history of the owens valley fault and adjacent faults and to consider the role of segmentation as well as splay and distributed faulting in comparisons of displacement data among different sites along the entire 100 10 km length of the owens valley fault

late quaternary paleoseismology of the southern steens fault zone northern nevada the 192 km long steens fault zone is the most prominent normal fault system in the northern basin and range province of western north america we use trench mapping and radiometric dating to estimate displacements and timing of the last three surface rupturing earthquakes e1 e3 on the southern part of the fault south of denio nevada coseismic displacements range from 1 1 to 2 2 0 5 m and radiometric ages indicate earthquake times of 11 5 2 0 ka e3 6 1 0 5 ka e2 and 4 6 1 0 ka e1 these data yield recurrence intervals of 5 4 2 1 k y between e3 and e2 1 5 1 1 k y between e2 and e1 and an elapsed time of 4 6 1 0 k y since e1 the recurrence data yield variable interval slip rates between 0 2 0 22 and 1 5 2 3 mm yr but slip rates averaged over the past 18 k y 0 24 0 06 mm year are similar to long term 8 5 12 5 ma slip rates 0 2 0 1 mm yr measured a few kilometers to the north we infer from the lack of significant topographic relief across the fault in bog hot valley that the fault zone is propagating southward and may now be connected with a fault at the northwestern end of the pine forest range displacements documented in the trench and a rupture length of 37 km indicate a history of three latest quaternary earthquakes with magnitudes of m 6 6 7 1 on the southern part of the steens fault zone

temporal correspondence between pluvial lake highstands in the southwestern us and heinrich event 1 pluvial lakes were abundant in the southwestern united states during pleistocene glaciations particu larly in the great basin many of these lakes occupied closed basins therefore fluctuations of their water surface elevations are valuable sources of paleoclimate information histories of the largest lakes are well constrained whereas dozens of smaller lakes that were present in this region have received relatively little scientific attention given their dimensions these smaller lakes were climatically sensitive and can offer important information about quaternary climate variability here we present new ages for the highstands of three previously undated small lakes based on radiocarbon dating of gastropod shells recovered from beach ridges these results are combined with other published and unpublished 14 c ages to yield an extensive compilation of highstand shoreline ages for lakes of all sizes throughout the southwestern us the results indicate that although some lakes reached highstands during the last glacial maximum the strongest temporal correspondence is between highstands and heinrich event h1 these results are consistent with speleothem based reconstructions of effective moisture in the southwestern us which show increased precipitation during stadials of the last glacial cycle copyright 2012 john wiley sons ltd

wind driven bottom currents and related sedimentary bodies in lake saint jean quebec canada lakes are major depositional systems for which the related depositional processes have long been considered relatively simple breaking this statement this study presents a detailed analysis of deposits in lake saint jean the third largest natural lake in quebec in addition to postglacial deltaic and coastal depositional systems fringing the lake current controlled features such as a large subaqueous prograding wedge and three sediment drifts have been identifi ed in its central portion based on two dimensional 2 d acoustic high resolution subbottom profiles the large subaqueous prograding wedge is a 4 km long and up to 15 m thick heterolithic shelf like construction in the southeastern part of the lake the three sediment drifts are 0 1 0 5 km long and 2 5 mthick mud mounds distributed on the lake floor in the central portion of the lake diatom analyses and radiocarbon dating show that the development of these current controlled features occurred during the lacustrine phase after the disconnection with the postglacial marine laflamme gulf at 8 5 cal k y b p depositional facies show evidence of recurrent bottom current activity related deposits alternate with pelagic sedimentation stages characterized by the settling of mud and biogenic accumulations we investigated the origin of bottom currents using a numerical simulation symphonie an oceanographic model with the aim of modeling wind induced lake scale water circulation simulations suggest that the subaqueous prograding wedge and the three sediment drifts result from wind induced bottom currents generated by storm events having wind speed greater than 10 m s 1 such strong winds are able to significantly affect sedimentation in the central portion of lake saint jean the resulting wind induced sedimentary features were integrated into a refi ned lacustrine depositional model that summarizes the evolution of a group of water bodies referred to as wind driven water bodies this study applies a new tool for lake strata characterization and highlights the potential diffi culty in differentiating them from marine deposits in the geological record

controls of tufa development in pleistocene lake bonneville utah abstract prominent tufa localities along the provo level 14 000 14c yr b p shoreline in pleistocene lake bonneville have been characterized in detail three types of tufa are recognized capping tufa beachrock and capping tufa over beachrock capping tufa and beachrock are end members of a continuum based on variable clastic content all three types typically occur on headland environments that had stable substrate and little sediment input tufa development correlates with bedrock exposure and landform orientation which in turn are correlated documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr page

interannual variability of the gulf of alaska eddy field 1 regions of high eddy kinetic energy eke in the gulf of alaska goa calculated from altimetry data denote formation regions and translation pathways for eddies high eke is observed along the shelf break in winter and spring with lower values in summer and autumn three regions of high eke are examined in detail in the eastern goa particularly high eke occurred in 1998 in the northwestern goa eddies were observed quasi annually between 1999 and 2004 but were less frequent prior to that time or in 2005 and 2006 eddies northeast of kodiak island have been implicated in high offshelf chlorophyll concentrations observed from ocean color satellites correlations between eke and chlorophyll concentration are significant there suggesting that eke may be valuable for predicting phytoplankton blooms in this region

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

megalakes in the sahara a review the sahara was wetter and greener during multiple interglacial periods of the quaternary when some have suggested it featured very large mega lakes ranging in surface area from 30 000 to 350 000 km2 in this paper we review the physical and biological evidence for these large lakes especially during the african humid period ahp 11 5 ka megalake systems from around the world provide a checklist of diagnostic features such as multiple well defined shoreline benches wave rounded beach gravels where coarse material is present landscape smoothing by lacustrine sediment large scale deltaic deposits and in places tufas encrusting shorelines our survey reveals no clear evidence of these features in the sahara except in the chad basin hydrologic modeling of the proposed megalakes requires mean annual rainfall 1 2 m yr and a northward displacement of tropical rainfall belts by 1000 km such a profound displacement is not supported by other paleo climate proxies and comprehensive climate models challenging the existence of megalakes in the sahara rather than megalakes isolated wetlands and small lakes are more consistent with the sahelo sudanian paleoenvironment that prevailed in the sahara during the ahp a pale green and discontinuously wet sahara is the likelier context for human migrations out of africa during the late quaternary

coarse clastic barrier beaches a discussion of the distinctive dynamic and morphosedimentary characteristics abstract coarse clastic barriers are common on mid and high latitude coasts they possess a morphosedimentary and dynamic distinctiveness which sets them apart from sandy fineclastic barrier forms the reflective nature of the seaward barrier favors the development of zero mode sub harmonic edge waves particularly during long period swells 10 20 s manifest in the formation of high level cusps in some circumstances the pattern of recent overwashing of the barrier is related to cusps lack of distinct tidal passes due partly to the high seepage potential of coarse barriers means that very little sediment is transported seaward thus the barriers roll steadily onshore and sections show a variety of washover facies related to the volume of overwash surges

lake size variations in the lahontan and bonneville basins between 13 000 and 9000 14c yr b p abstract recessions of lakes lahontan and bonneville that commenced 13 500 14 c yr b p were interrupted at 11 500 14 c yr b p in the lahontan basin and 12 200 14 c yr b p in the bonneville basin by relatively large perturbations in lake level that persisted for 2000 years minor glacial readvances in the sierra nevada and white mountains of california nevada occurred during the latter half of this interval between 11 000 and 9700 14 c yr b p the hydrologic response of lakes lahontan and bonneville and the mountain glacial advances were concurrent with the allerod younger dryas climatic intervals recorded in vegetational and glacial records of western and central europe

formation of the haida 1998 oceanic eddy 1 two large mesoscale anticyclonic eddies formed along the west coast of the queen charlotte islands of western canada in early 1998 altimetry measurements from topex poseidon and ers 2 satellites suggest that these eddies first appeared near cape st james at the southern tip of the islands the eddies merged in june to form haida 1998 the highest eddy ever observed in the region currents near cape st james in winter follow complicated patterns attributed to tidal rectification and pressure driven outflow from hecate strait the adjustment of these flows to the bathymetric features likely contributes to the formation of haida eddies eddies that first appear farther north along the west coast of the queen charlotte islands are set up by other processes such as baroclinic instability

paleoseismic transect across the northern great basin 1 the relationship of strain accumulation to strain release over different timescales provides insight to the dynamics structural development and spatial and temporal pattern of earthquake recurrence in regions of active tectonics the great basin physiographic province of the western united states is one of the earth s broadest regions of ongoing continental extension encompassing an area reaching 800 km in width between the sierra nevada to the west and wasatch mountains to the east we present observations arising from excavations scarp profiling optically stimulated luminescence and radiocarbon dating to place limits on the late pleistocene paleoseismic history of faults bounding eight ranges across the interior of the northern great basin specifically the shawave hot springs humboldt sonoma shoshone tuscarora dry hills and pequop ranges combining the observations with similar previously published studies within and at the margins of the great basin yields a transect that extends eastward across the basin between the 40th and 41st parallels the sum of observations provides a picture of the patterns and rates of earthquake recurrence over the region during the last 20 45 kyr that may be compared to patterns of contemporary seismicity and recently reported measures of strain accumulation across the area using gps the recurrence rate of large surface rupture paleoearthquakes along ranges at the margins of the great basin is systematically greater than observed along ranges in the interior the pattern is similar to seismological and geodetic measurements that show levels of background seismicity and strain accumulation are also concentrated along the margins of the great basin an east west extension rate across the interior of the great basin on the order of 1 2 mm yr 1 strain rate of 1 nstrain yr 1 over the last 20 45 kyr is estimated by summing the record of paleoseismic displacements across the 400 km breadth of the transect as compared to 2m m yr 1 of strain accumulation indicated by a recently reported analysis of a collinear gps survey the comparison is hindered by significant uncertainties coupled to the geologic rate estimate the transect also crosses the northern limit of the central nevada seismic belt the central nevada seismic belt is defined by a north northeast trending alignment of historical surface rupture earthquakes increased levels of background seismicity and strain accumulation rates greater than observed elsewhere in the interior of the great basin the reported recurrence rate of late pleistocene surface rupture earthquakes within the central nevada seismic belt is also generally greater than observed along our transect the observations when taken together suggest that the characteristics of strain release observed historically within the central nevada seismic belt have been operative over the latest pleistocene and that the apparently greater rates of strain accumulation and release in the central nevada seismic belt are diminished or less localized in regions to the north and east thus while the historical alignment of surface ruptures that defines the central nevada seismic belt remains a unique clustering of earthquakes in time and space the likelihood of the cluster at its observed location appears greater than would be expected to the north or eastward in the interior of the great basin

seismic stratigraphy buried beach ridges and contourite drifts the late quaternary history of the closed lago cardiel basin argentina 49 s the results of a seismic stratigraphic analysis of a closed lake basin lago cardiel in southernmost south america are reported very few high resolution continental records spanning the late quaternary have been obtained from this region seismic sequence stratigraphic analysis allows a reconstruction of lake level variations two major hiatuses of unknown age occurred during the early evolution of the basin with the deposition of an alluvial fan in a restricted area in the intervening time period following the development of a relatively shallow lake during the late pleistocene and a short desiccation pulse around 11 220 14c yr bp a transgression of over 135 m occurred at the beginning of the holocene the transgression was associated with the formation of beach ridges preserved in the lake stratigraphy on the floor of the modern lago cardiel at four different elevations the preservation of largely unreworked beach ridges indicates a stepwise rise in the lake level there is no seismic evidence of a major lowering of the lake below modern level during the entire holocene deposition since the mid holocene is marked by strong lateral differences in sediment accumulation with a depocentre slightly to the north of the basin midpoint and a pronounced mounded distribution seismic reflection geometries as well as sedimentological characteristics indicate a lacustrine contourite drift covering an area of 80 100 km2 as lago cardiel is under the influence of westerly winds these most likely drove lake circulation the identification of drowned beach ridges and of contourite drifts illustrates that high resolution seismic stratigraphy is not only a powerful tool in reconstructing past lake level elevations for closed lake basins but it can also provide information about the rate of lake level changes and the presence and strength of lake currents

refining fault slip rates using multiple displaced terrace risers an example from the honey lake fault ne california usa abstract faulted terrace risers are semi planar features commonly used to constrain quaternary slip rates along strike slip faults these landforms are difficult to date directly and therefore their ages are commonly bracketed by age estimates of the adjacent upper and lower terrace surfaces however substantial differences in the ages of the upper and lower terrace surfaces a factor of 2 4 difference observed globally produce large uncertainties in the slip rate estimate in this investigation we explore how the full range of displacements and bounding ages from multiple faulted terrace risers can be combined to yield a more accurate fault slip rate we use 0 25 m cell size digital terrain models derived from airborne lidar data to analyze three sites where terrace risers are offset right laterally by the honey lake fault in ne california usa we use ages for locally extensive subhorizontal surfaces to bracket the time of riser formation an upper surface is the bed of abandoned lake lahontan having an age of 15 8 0 6 ka and a lower surface is a fluvial terrace abandoned at 4 7 0 1 ka we estimate lateral offsets of the risers ranging between 6 6 and 28 3 m median values a greater than fourfold difference in values the amount of offset corresponds to the riser s position relative to modern stream meanders the smallest offset is in a meander cutbank position whereas the larger offsets are in straight channel or meander point bar positions taken in isolation the individual terrace riser offsets yield slip rates ranging from 0 3 to 7 1 mm a however when the offset values are collectively assessed in a probabilistic framework we find that a uniform linear slip rate of 1 6 mm a 1 4 1 9 mm a at 95 confidence can satisfy the data within their respective uncertainties this investigation demonstrates that integrating observations of multiple offset elements crest midpoint and base from numerous faulted and dated terrace risers at closely spaced sites can refine slip rate estimates on strike slip faults

level of lake lahontan during deposition of the trego hot springs tephra about 23 400 years ago abstract the trego hot springs tephra bed is a silicic tephra about 23 400 yr old found at several localities in pluvial lake sediments in northern nevada southern oregon and northeastern california it has been characterized petrographically by the major and minor element chemistry of its glass and by its stratigraphic position with respect to other tephra layers at a newly described locality on squaw creek northwest of gerlach nevada at the north end of the smoke creek desert trego hot springs tephra has been found in sediments of the sehoo and indian lakes formations the depositional environments of these sediments show that when the tephra fell pluvial lake lahontan stood between 1256 and 1260 m and that immediately thereafter the lake rose to at least 1275 m these data corroborate earlier findings by benson quaternary research 9 300 318 from radiometric dating of calcareous tufa however the lake lahontan area has been affected by isostatic subsidence and rebound in response to changing water loads so that caution is required in the use of lakeshore elevations in correlation

late pleistocene highstand and recession of a small high altitude pluvial lake jakes valley central great basin usa abstract models of factors controlling late pleistocene pluvial lake level fluctuations in the great basin are evaluated by dating lake levels in jakes valley jakes lake rose to a highstand at 13 870 50 14c yr b p receded to a stillstand at 12 440 50 14c yr b p and receded steadily to desiccation thereafter the jakes lake highstand is roughly coincident with highstands of lakes bonneville lahontan and russell the rise to highstand and recession of jakes lake were most likely controlled by a storm track steered by the polar jet stream the final stillstand of jakes lake helps constrain timing of northward retreat of the polar jet stream during the pleistocene holocene transition

lacustrine cave carbonates novel archives of paleohydrologic change in the bonneville basin utah usa records of past changes in lake levels and lake water isotopic composition in closed basins provide key insights into past variations in the hydrological cycle however these records are often limited by dating precision and temporal resolution here we present data from lacustrine cave carbonates a previously unexplored class of carbonates that comprise a promising new archive of past hydrologic changes in the bonneville basin of the northeastern great basin usa these dense carbonates precipitated within caves crevices and other protected spaces flooded by lake bonneville during its highstand in the last glacial period we report on deposits in cathedral and craners caves located 50 km apart at similar elevations approximately 100 m above the modern great salt lake and almost 200 m below lake bonneville s highstand shoreline carbonates from the two caves show similar chronologies mineralogical transitions isotopic compositions and uranium concentrations these findings suggest that lacustrine cave carbonates record changes in lake level and in the isotopic composition and chemistry of lake water importantly the deposits can be precisely dated by u th methods providing the first records of lake bonneville s water balance changes tied to precise u th ages close agreement between paired u th and calibrated 14 c ages in the deposits suggests a minimal o200 a carbon reservoir effect in the lake and allows 14 c dating to be used for age control in portions of the deposits less suitable for u th dating we use ages for the onset and cessation of lacustrine cave carbonate deposition to offer new constraints on past changes in lake level and the carbonate saturation state of lake water we also present precisely dated high resolution oxygen and uranium isotope records from the deposits within a first phase of deposition reflecting the lake s transgression between 26 and 18 ka our isotopic data suggest a large influx of freshwater during heinrich stadial 2 a hiatus in deposition beginning at 18 270 3 ka may be the result of freshening related to the lake s overflow calcite deposition resumes at cathedral cave at 16 470 2 ka suggesting that basin overflow had ceased by this time and that the lake s calcite saturation state had increased andd 18 o values increase markedly after 15 9 ka consistent with drying at this time these data imply that the lake s deglacial regression began well before the bolling warming cessation of this second phase of deposition at 14 770 2 ka coincident with the bolling warming may reflect the lake s drop below cathedral cave s elevation a final stage of aragonite deposition between 13 8 and 13 6 ka differs from the underlying facies and may not reflect deposition from lake waters filling the cave

particle size and shape in pebble beach sedimentation an in depth investigation was made of beach gravel fabrics at two beach sites located on the glamorgan heritage coast wales u k granulometric data from 31 080 pebbles were obtained and analysis confirmed the existence of a basic shape differentiation structure when the b axis was used at gileston beach a low energy location and nash beach a high energy location the use of the b axis in size and shape analysis seems to have led some workers to incorrect rejection of size as a factor in determining the transportational and depositional potential of a particle an inferred energy model can be constructed where the influence of particle size on sorting is predominant when energy conditions are high and particle shape factors predominate when energy conditions are low the c axis standard deviation value was the most effective discriminator of variation in shore parallel sedimentation structures at both beaches for shore normal structural discrimination the c axis mean and standard deviation values were the most effective

morphology and stratigraphy of small barrier lagoon systems in maine abstract the coast of maine contains over 200 individual barrier lagoon systems most quite small with an aggregate length of nearly 100 km although they represent less than 5 of the tidally influenced coastline of maine they are widely distributed and occur in a variety of dynamic regimes and physiographic regions their morphology and backbarrier stratigraphy are different from better studied coastal plain systems and provide important clues to the holocene evolution of the maine coast in a study of geomorphic form and backbarrier stratigraphy inlet processes and holocene sea level rise have been identified as the principal controls on coarse grained barrier stratigraphy barriers in maine are found in five distinct geomorphic forms identified herein as barrier spits pocket barriers double tombolos cuspate barriers and looped barriers the few long sandy beaches in southwestern maine are mostly barrier spits the remainder of the barrier types is composed primarily of gravel or mixed sand and gravel the barriers protect a variety of backbarrier environments fresh and brackish ponds lagoons and fresh and saltwater marshes the barriers may or may not have inlets normal wave action coarse grain size and a deeply embayed coast result in barriers with steep reflective profiles several meters above mhw occasional storm events completely wash over the barriers building steep lobate gravel fans along their landward margin few if any extensive storm layers are recognized as extending into the distal backbarrier environments however during sea level rise and landward barrier retreat this abrupt storm generated transition zone inters the backbarrier sediments statistical comparisons of barrier morphology location and backbarrier environment type with backbarrier stratigraphy show that holocene backbarrier stratigraphy is best predicted by the modern backbarrier environment type this in turn is influenced most by the absence or presence and long term stability or instability of a tidal inlet geomorphic barrier form and location in coastal geomorphic compartments show little or no correlation with backbarrier stratigraphy in contrast to previous classifications of barrier lagoon systems based primarily on sandy coastal plain examples in maine the shape or origin of the backbarrier system is relatively unimportant the presence or absence of a tidal inlet is of paramount importance in shaping the holocene stratigraphy of the backbarrier region

stratigraphy and chronology of offshore to nearshore deposits associated with the provo shoreline pleistocene lake bonneville utah abstract stratigraphic descriptions and radiocarbon data from eleven field locations are presented in this paper to establish a chronostratigraphic framework for offshore to nearshore deposits of lake bonneville based on key marker beds and geomorphic position the deposits are interpreted to have accumulated during the period from the late transgressive phase through the overflowing phase into the regressive phase of the lake radiocarbon ages of sediments associated with the provo shoreline indicate that lake bonneville dropped rapidly from the provo shoreline at about 12 600 14c yr bp 15 000 cal yr b p the presence of one or more sand beds in the upper part of the provo aged marl indicates rapid lowering of lake level or storm events at the end of the provo episode an accurate understanding of the timing and nature of lake bonneville s climate driven regression from the provo shoreline is critical to correlations with records of regional and hemispheric climate change the rapid descent of the lake from the provo shoreline correlates with the decline of lakes lahontan and estancia and with the onset of the b o lling aller o d warming event

a high resolution assimilating tidal model for the northeast pacific ocean a high resolution nonlinear barotropic finite element tidal model is developed for removing tidal elevations from satellite altimeter observations in the northeast pacific ocean surface elevations and currents for the constitutents m2 s2 n2 k2 k1 o1 p1 and q1 are computed using boundary forcing from the oregon state university global tidal model tpxo 3 and the effects of the tidal potential earth tide and ocean self attraction and loading amplitudes and phases computed from the harmonic analyses of altimeter time series at crossover locations along the tracks of the topex poseidon satellite are assimilated into the model and the corrected harmonics are compared with pelagic and coastal tide and pressure gauge measurements and with the tpxo 3 and fes95 2 1 global models diurnal tidal currents along the british columbia and alaska continental shelves are shown to be strongly influenced by the presence of continental shelf waves the surface manifestation of these waves is clearly evident in k1 coamplitude plots k1 and m2 energy fluxes are calculated along these shelves and the potential generation of internal tides is discussed barotropic tidal dissipation is estimated in several key subregions and the m2 total for the gulf of alaska is found to be approximately half that of previous estimates

processes and timescales by which a coastal gravel dominated barrier responds geomorphologically to sea level rise story head barrier nova scotia sea level rise slr is considered to be important for barrier behaviour when barriers are swash aligned and single crested which is typical of only one part of a barrier s lifeterm under such conditions gravel barrier retreat rate correlates with mesoscale sub decadal 102 a slr rate is the critical control on barrier retreat as mesoscale slr variation in combination with surge potential is able to raise water level to the elevation threshold sufficient for barrier overwash and hence drive barrier retreat

a revised chronology for the last pleistocene lake cycle in the central lahontan basin radiocarbon dates of plant materials from packrat middens in caves below the elevation of the last high stand of pleistocene lake lahontan in conjunction with radiocarbon dates of ancient archaeological materials provide evidence that the last high stand terminated before 12 070 yr b p this new information suggests that the last major fluctuation in the level of lake lahontan was approximately synchronous with those of lakes bonneville and russell and that these three lakes probably responded contemporaneously to the same regional paleoclimatic changes

chronology of latest pleistocene mountain glaciation in the western wasatch mountains utah u s a abstract understanding the timing of mountain glacier and paleolake expansion and retraction in the great basin region of the western united states has important implications for regional scale climate change during the last pleistocene glaciation the relative timing of mountain glacier maxima and the well studied lake bonneville highstand has been unclear however owing to poor chronological limits on glacial deposits here this problem is addressed by applying terrestrial cosmogenic 10be exposure dating to a classic set of terminal moraines in little cottonwood and american fork canyons in the western wasatch mountains the exposure ages indicate that the main phase of deglaciation began at 15 7 1 3 ka in both canyons this update to the glacial chronology of the western wasatch mountains can be reconciled with previous stratigraphic observations of glacial and paleolake deposits in this area and indicates that the start of deglaciation occurred during or at the end of the lake bonneville hydrologic maximum the glacial chronology reported here is consistent with the growing body of data suggesting that mountain glaciers in the western u s began retreating as many as 4 ka after the start of northern hemisphere deglaciation at ca 19 ka

lake levels and sequence stratigraphy of lake lisan the late pleistocene precursor of the dead sea lake lisan the late pleistocene precursor of the dead sea existed from 70 000 to 15 000 yr b p it evolved through frequent water level fluctuations which reflected the regional hydrological and climatic conditions we determined the water level of the lake for the time interval 55 000 15 000 cal yr b p by mapping offshore nearshore and fan delta sediments by application of sequence stratigraphy methods and by dating with radiocarbon and u series methods during the studied time interval the lake level fluctuated between 340 and 160 m below mean sea level msl between 55 000 and 30 000 cal yr b p the lake evolved through short term fluctuations around 280 290 m below msl punctuated at 48 000 43 000 cal yr b p by a drop event to at least 340 m below msl at 27 000 cal yr b p the lake began to rise sharply reaching its maximum elevation of about 164 m below msl between 26 000 and 23 000 cal yr b p then it began dropping and reached 300 m below msl at 15 000 cal yr b p during the holocene the lake corresponding to the present dead sea stabilized at ca 400 m below msl with minor fluctuations the hypsometric curve of the basin indicates that large changes in lake area are expected at above 403 and 385 m below msl at these elevations the lake level is buffered lake lisan was always higher than 380 m below msl indicating a significantly large water contribution to the basin the long and repetitious periods of stabilization at 280 290 m below msl during lake lisan time indicate hydrological control combined with the existence of a physical sill at this elevation crossing this sill could not have been achieved without a dramatic increase in the total water input to the lake as occurred during the fast and intense lake rise from 280 to 160 m below msl at 27 000 cal yr b p

crestal overtop and washover sedimentation on a fringing sandy gravel barrier coast carnsore point southeast ireland abstract storm sedimentation on a fringing sandy gravel barrier system in southeast ireland is examined recent wave overtopping and overwashing during severe onshore storms have resulted in a distinctive pattern of crest and backbarrier sedimentation this is not easily matched with available models of washover sedimentation drawn from the barrier islands of the eastern united states beach crest overtopping occurs at heights up to 6 m mhws and is related to the development of upper beach swash ramps that are plastered against storm wave eroded dune scarps located at the barrier crest ramp sediments comprise coarse basal beach gravels overlain by coarsening upward units and finally topped by distinctive seawarddipping fine grit coarse sand couplets in places where ramps reach the dune cre t overtopping swash has deposited a fine marine gravel veneer

historic surface faulting and paleoseismicity in the area of the 1954 rainbow mountain stillwater earthquake sequence central nevada the rainbow mountain area was the site of three surface rupturing earthquakes on 6 july and 23 august 1954 more than 50 field measurements of surface offsets constrain the distribution of slip along the discontinuous and distrib uted rupture zone that formed during the earthquake sequence vertical offsets reach a maximum of 0 8 m with the average vertical offset being 0 2 m in contrast to original reports we see evidence for a right lateral component of slip along portions of the rupture zone including offset stream channels 0 5 1 0 m left stepping en echelon scarps and a well preserved 100 m long mole track the right slip com ponent is consistent with focal plane solutions for the events and recent geodetic results previously unmapped surface ruptures now extend the known rupture length of the sequence by 25 km to a total of 70 km surface ruptures along the previously unmapped fourmile flat fault are subparallel to and form a 10 km left step to the southeast of the rainbow mountain fault event locations and anecdotal information indicate that the fourmile flat ruptures represent minor primary surface rupture associated with the large 6 july aftershock triggered 11 hr after the initial 6 july rainbow mountain event the paleoseismic histories of the rainbow mountain and fourmile flat faults as recorded in natural and trench exposures are different although both faults experi enced three post 15 ka surface rupturing events including 1954 bracketing ages for triultimate events on both faults do not overlap however constraints on the penultimate event for the rainbow mountain and triultimate event for the fourmile flat fault do overlap slightly allowing the possibility that they may have ruptured close in time as in 1954 the holocene slip rate for the fourmile flat fault 0 40 mm yr is similar to the post latest pleistocene rate for the rainbow mountain fault 0 20 0 46 mm yr even though the total length of the fourmile flat 10 km is much shorter than the overall length of the rainbow mountain rupture zone 60 km indicating that even minor faults can be important for assessing regional strain rates and patterns

lake bonneville constraints on lithospheric thickness and upper mantle viscosity from isostatic warping of bonneville provo and gilbert stage shorelines the deformed shorelines of the late pleistocene lake bonneville provide an excellent opportunity to analyze the response of the earth to surface loads of relatively short wavelengths 400 km and short duration 30 kyr recently revised estimates of the lake loading history and an expanded compilation of shoreline elevations for the bonneville 1550 m provo 1440 m and gilbert 1300 m shorelines have prompted us to reexamine the deflection the earth model we use is identical with that employed by nakiboglu and lambeck and consists of an elastic plate overlying a maxwell viscoelastic channel and a rigid base our calculation differs from that of nakiboglu and lambeck in two respects we used a significantly more detailed load model and we compared our results with observations from three distinct shorelines the lake elevation history spans 32 kyr in 18 piecewise linear segments the water load is computed at each time step from a digital terrain model 4 4 km cell size and a specified lake elevation we find that the use of three separate shorelines significantly reduces the acceptable region of parameter space the effective elastic lithospheric thickness is 23 2 km the mantle viscosity is 1 2 0 2 1020 pa s and the depth to a significant viscosity increase is no less than 300 km though it might be much more examination of the residual deflections differences between observed and computed shoreline elevations reveals a regional tilt down to the ne of 6 10 5 which we attribute to collapse of the peripheral bulge produced by the laurentide ice sheet

dynamic ocean topography for the northeast pacific and its continental margins 1 estimates of dynamic ocean or sea surface topography based on satellite altimetry and gravity observations generally become degraded as they approach land in this study dynamic ocean topography for the northeast pacific ocean is computed independently of satellite observations using a high resolution model and seasonal climatologies of temperature salinity and wind stress comparisons with estimates based on satellite gravity and altimetry measurements show reasonable agreement in the deep ocean but are poor on continental margins where the ocean model estimates not only reveal significant seasonal differences but are also shown to be reasonably accurate when compared with satellite altimetry and coastal tide gauge measurements the dynamic ocean topography estimates provided here will permit more accurate calculations of the geoid and satellite altimeter absolute heights and currents

late quaternary climate induced lake level variations in lake peten itza guatemala inferred from seismic stratigraphic analysis abstract we used seismic images and sedimentary data from piston cores to conduct a sequence stratigraphic analysis of sediments in lake peten itza northern guatemala our results document lake level fluctuations in this lowland neotropical region that were related to glacial to interglacial climate change during the late pleistocene a bathymetric survey of lake peten itza area 100 km2 revealed a maximum water depth of 160 m and the existence of a deep cryptodepression that extends 50 m below modern sea level the great depth suggests that the basin held water even during arid conditions associated with full glacial periods lake peten itza may thus possess the only long continuous lacustrine sediment record of late pleistocene environmental and climate change in the lowland neotropics two seismic reflection campaigns imaged the subsurface basin sediments that overlie basement the sediment package was divided into four major seismic sequences t g r and b sequences are separated by unconformities that represent depositional cycles related to lake level fluctuations sediments of the uppermost sequence t were recovered and radiocarbon dated in kullenberg piston cores taken along a water depth transect seismic profiles reveal a basin wide paleoshoreline just below sequence t at 56 m below present lake level this constructional feature formed during a lowstand of the last glacial period when the lake was reduced to only 13 of its present volume in cores taken landward of the paleoshoreline late glacial age deposits consist of paleosols indicating subaerial exposure basinward of the shoreline sediments are composed of dense gypsum sands and interbedded silty clays reflecting authigenic gypsum formation under arid climate conditions the top of the soil horizon and cessation of gypsum precipitation are represented by a strong seismic reflection t it marks the base of the uppermost seismic sequence t and is dated in several cores between 11 1 and 10 2 cal kyr bp lake level rose quickly at this time in response to a shift from arid to humid climate conditions at the late glacial early holocene transition we infer a similar sediment response to climate variations in the older stratigraphic sequences g r and b related to earlier glacial to interglacial and stadial to interstadial cycles older sequences are also distinguished from one another by erosional unconformities that probably represent major lake level falls future recovery of the older stratigraphic record by drilling in lake peten itza will provide ages for these older units and enable us to test the depositional model inferred from seismic stratigraphy

chronology of expansion and contraction of four great basin lake systems during the past 35 000 years abstract during the past 35 000 years lake bonneville lake russell and lake searles underwent a major period of lake level change the lakes were at moderate levels or dry at the beginning of the period and seem to have achieved highstands between about 15 000 and 13 500 yr b p the rise of lake lahontan was gradual but not continuous in part because of topographic constraints intrabasin spill lake lahontan also had an oscillation in lake level at 15 500 yr b p radiocarbon age estimations for materials that were deposited in the lake basins indicate that lake bonneville rose more or less gradually from 32 000 yr b p and had major oscillations in level between 23 000 and 21 000 yr b p and between 15 250 and 14 500 yr b p lake russell and lake searles had several major oscillations in lake level between 35 000 and 14 000 yr b p the timing and exact magnitude of the oscillations are difficult to decipher but both lakes may have achieved multiple highstand states all four lakes may have had nearly synchronous recessions between about 14 000 and 13 500 yr b p after the recessions the lakes seem to have temporarily stabilized or experienced a minor increase in size between about 11 500 and 10 000 yr b p these data provide circumstantial evidence that the younger dryas event affected climate on at least a hemispheric scale during the holocene the four lakes remained at low levels and small oscillations in lake level occurred an important aspect of the lake level data is the accompanying expansion of lake surface area at the time of the last highstand lake bonneville and lake lahontan had surface areas about 10 times larger than their mean historical reconstructed areas whereas lake russell and lake searles had surface areas about 5 times larger than their mean historical reconstructed areas differences in the records of effective wetness may have been due to the locations of the basins relative to the position of the jetstream or they may have resulted from lake atmosphere feedback processes

lake level variation in the lahontan basin for the past 50 000 years selected radiocarbon data on surficial materials from the lahontan basin nevada and california provide a chronology of lake level variation for the past 50 000 yr a moderate sized lake connected three western lahontan subbasins the smoke creek black rock desert subbasin the pyramid lake subbasin and the winnemucca dry lake subbasin from about 45 000 to 16 500 yr b p between 50 000 and 45 000 yr b p walker lake rose to its sill level in adrian valley and spilled to the carson desert subbasin by 20 000 yr b p lake level in the western lahontan subbasins had risen to about 1265 m above sea level where it remained for 3500 yr by 16 000 yr b p lake level in the western lahontan subbasins had fallen to 1240 m this recession appears synchronous with a desiccation of walker lake however whether the walker lake desiccation resulted from climate change or from diversion of the walker river is not known from about 15 000 to 13 500 yr b p lake level rapidly rose so that lake lahontan was a single body of water by 14 000 yr b p the lake appears to have reached a maximum highstand altitude of 1330 m by 13 500 yr b p a condition that persisted until about 12 500 yr b p at which time lake level fell 100 m no data exist that indicate the level of lakes in the various subbasins between 12 000 and 10 000 yr b p during the holocene the lahontan basin was the site of shallow lakes with many subbasins being the site of one or more periods of desiccation the shape of the lake level curve for the three western subbasins indicates that past changes in the hydrologic balance and hence climate of the lahontan basin were large in magnitude and took place in a rapid step like manner the rapid changes in lake level are hypothesized to have resulted from changes in the mean position of the jet stream as it was forced north or south by the changing size and shape of the continental ice sheet

the lake lahontan highstand age surficial characteristics soil development and regional shoreline correlation abstract the lake lahontan basin has been the site of numerous pluvial lakes during the pleistocene we address the question of whether or not the highest remnant shoreline features around the perimeter of the lake were produced during the most recent sehoo highstand 13 ka the penultimate eetza highstand 140 280 ka or both to do so we document surficial characteristics morphologic preservation and soil development on multiple sehoo beach barriers in the jessup embayment to define the range in characteristics displayed by latest pleistocene beach features sehoo barriers generally exhibit original constructional morphology that has been little modified by erosion soils developed on sehoo barriers are generally thin and weakly developed and are strongly influenced by the introduction of eolian fines into the predominately clast supported coarse beach gravels similar observations from 13 other highstand barriers and from seven older than latest pleistocene paleosols located around the basin form the basis for a regional comparison based on similar characteristics including the degree of morphologic preservation and weak soil development we conclude that the widespread and nearly continuous high shoreline around the perimeter of lake lahontan dates from the most recent major lake cycle in all areas except in the walker lake subbasin in the walker lake subbasin isolated early to middle pleistocene lacustrine outcrops and landforms are elevated as much as 70 m above the late pleistocene limit but are differentiated by their degraded form and lack of continuity around the subbasin similar unambiguous landforms were not observed elsewhere and at similar elevations in the northern subbasins of lake lahontan

estimating drawdown magnitudes of the mediterranean sea in the levant basin during the lago mare stage of the messinian salinity crisis abstract the messinian salinity crisis 5 97 5 33 ma is one of the most dramatic sea level change events in the global geological record during this event marine connection between the atlantic ocean and the mediterranean sea was restricted and episodically blocked while division of the messinian salinity crisis to three major stages is well established and accepted the scale of sea level change at each stage is still debated the magnitudes of the mediterranean fluctuations throughout the messinian salinity crisis have implications for contemporary connectivity between the eastern and western mediterranean basins during the third stage of the messinian salinity crisis commonly known as the lago mare mediterranean sea level fluctuated repeatedly lago mare drawdowns in the eastern mediterranean were estimated earlier to vary between we propose that during the lago mare ravinement along a continuously regressing transgressing coastline abraded the upper continental margin offshore israel the mediterranean regressed to a depth of 380 550 m below present day mean sea level and the eroded strata were evacuated downslope and deposited basinward of this depth as wedge shape clastic complexes during relatively short intervals sea level receded to altitudes 100 m below the erosional surface these sea level recessions exposed a pronounced inflection in the slope gradient to sub aerial processes generating knickpoints and headward migration of incising gullies these gullies developed later into channels conduits for sediment bypass fan deltas were deposited off these channels outlets a major sea level fall towards the end of the messinian salinity crisis reached 630 900 m below present day mean sea level streams incised into the exposed tops of the clastic wedges and fan deltas additionally meteoric water dissolved evaporites within the clastic complexes and formed sinkholes and dolines during this interval the mediterranean sea level fell to below the depth of the sicily sill which separated the eastern and western mediterranean basins this finding reinforces previously proposed paradigms which suggested that the messinian salinity crisis was terminated by spillover events from the atlantic ocean to the western mediterranean basin and consequently from the western to the eastern basin

possible connection between large volcanic eruptions and level rise episodes in the dead sea basin abstract the june 1991 pinatubo volcanic eruption perturbed the atmosphere triggering short term worldwide changes in surface and lower troposphere temperatures precipitation and runoff the following winter was anomalously wet in the levant with a 2 m increase in the dead sea level that created a distinct morphological terrace along the lake s shore given the global radiative and chemical effects of volcanogenic aerosols on climatic systems we tested the hypothesis that the 1991 92 winter shore terrace is a modern analogue to the linkage between past volcanic eruptions and a sequence of shore terraces on the cliffs around the dead sea basin dsb sixteen shore terraces detected using airborne laser scanning data were interpreted as indicating short term level rises due to episodes of enhanced precipitation and runoff during the dramatic drop in lake lisan s palaeo dead sea level at the end of the last glacial maximum the terraces were compared with a dated time series of volcanogenic sulfate from the gisp2 ice core and similar numbers of sulfate concentration peaks and shore terraces were found furthermore a significant correlation was found between so 4 concentration peaks and the heights of the terraces this correlation may indicate a link between the explosivity of past eruptions the magnitude of stratospheric injection and their impact on the northern hemisphere water balance the record of such short term climato hydrological effects is made possible by the dramatic desiccation of lake lisan detailed records of such events albeit rare because of their vulnerability and short longevity provide an important demonstration of global climatic teleconnections

putative shorelines in northern arabia terra mars 1 three putative shorelines first proposed by parker et al 1989 are topographically and morphologically evaluated within a 700 000 km2 study area in northern arabia terra mars results are consistent with a shoreline interpretation for the arabia and deuteronilus contacts but do not support the proposed acidalia shoreline the arabia contact follows an equipotential surface with a mean elevation of 3707 m and a mean deviation of 13 m for deuteronilus results suggest that the originally proposed shoreline represents two distinct regional shorelines because two separate portions of the original deuteronilus contact approximate equipotential surfaces of 4200 m 5 m and 4000 m 6 m for both the deuteronilus and arabia contacts there is geomorphic evidence for erosion and some landforms are similar to analogous terrestrial coastal landforms these results permit but do not prove the past existence of an ocean ponded within the northern lowlands possibly as recently as the amazonian

late holocene paleohydrology of walker lake and the carson sink in the western great basin nevada usa the late holocene histories of walker lake and the carson sink were reconstructed by synthesizing existing data in both basins along with new age constraints from key sites supplemented with paleohydrologic modeling the repeated diversions of the walker river to the carson sink and then back to walker lake caused walker lake level fluctuations spanning 50 m low lake levels at about 1000 750 and 300 cal yr bp are time correlative to the ages of fluvial deposits along the walker river paleochannel when flow was directed toward the carson sink the timing and duration of large lakes in the carson sink were further refined using moisture sensitive tree ring chronologies the largest lakes required a fourfold to fivefold increase in discharge spanning decades addition of walker river flow to the carson sink by itself is inadequate to account for the required discharge instead increases in the runoff coefficient and larger areas of the drainage basin contributing surface runoff may explain the enhanced discharge required to create these large lakes

uranium isotopes in soils as a proxy for past infiltration and precipitation across the western united states the intermittent presence of large pleistocene lakes in the southwestern interior of north america a region that is now a semi arid desert suggests repeated oscillations between profoundly different climatic conditions the origin of these shifts is still unresolved due to inconsistencies in existing climate proxy data for example pollen lake levels and oxygen isotopes in speleothems to resolve the inconsistencies in the water balance over the last 10 to 60 kyr we use uranium isotopic variations in secondary soil minerals to quantify net infiltration and precipitation along a north south transect in western north america we show that winter infiltration increased by 30 to 100 percent and precipitation by a lesser amount in the valleys of the great basin and mojave deserts between 60 and 26 ka this increase in infiltration and precipitation preceded the last glacial maximum lgm and the timing of most lake highstands in the region by 5 to 10 kyr respectively suggesting a possible last precipitation maximum lpm that coincided with a minimum in winter insolation subsequent decreases in infiltration and precipitation after the lgm can be reconciled with the timing of lake highstands if colder summer temperatures due to a minimum in summer insolation reduced lake evaporation the soil records combined with a range of proxy data suggest that seasonal insolation is the long term driver for large shifts in both precipitation and surface water variability in the region

fluvial response to an historic lowstand of the great salt lake utah understanding fluvial adjustments to base level changes benefits the fields of sequence stratigraphy geomorphology and petroleum geology this investigation is a modern case study of the channel dynamics of lee creek and the goggin drain two streams that are part of the jordan river drainage into the endorheic great salt lake of northern utah a lacustrine system that has experienced multiple decadal scale base level changes since 1965 the lake level has fluctuated in elevation more than 6 m transitioning from an historic lowstand 1284 m a s l and in 2009 2010 approaching an historic lowstand this study uses detailed aerial images fieldwork and lidar data to link the modern geomorphology and channel hydraulics to specific variations in sediment transport channel form and avulsion behavior although lee creek and the goggin drain are situated only a few kilometers apart and share similar shore zone gradients substrates and vegetation patterns and have been subjected to the same changes in lake level their channel forms have evolved very differently differences in discharge patterns are likely the most influential factor causing the meandering form of lee creek and the braiding channel of the goggin drain despite the differences in discharge total sediment eroded from the two streams is comparable and can be attributed to similar stream power unit stream width in the two streams although lee creek has not recently been avulsive three major avulsions of the goggin drain have taken place since 1965 two possible styles of avulsion are interpreted an allogenic response to changing base level and an autogenic response dictated by channel morphology and hydraulics despite a wealth of available information avulsions cannot be unequivocally attributed to one style or another caution should be used when attempting to link the complex process of avulsion to causal mechanisms copyright 2011 john wiley sons ltd

low footwall accelerations and variable surface rupture behavior on the fort sage mountains fault northeast california the fort sage mountains fault zone is a normal fault in the walker lane of the western basin and range that produced a small surface rupture 20 cm during an m l 5 6 earthquake in 1950 we investigate the paleoseismic history of the fort sage fault and find evidence for two paleoearthquakes with surface displacements much larger than those observed in 1950 rupture of the fort sage fault 5 6 ka resulted in surface displacements of at least 0 8 1 5 m implying earthquake moment magnitudes m w of 6 7 7 1 an older rupture at 20 5 ka displaced the ground at least 1 5 m implying an earthquake of m w 6 8 7 1 a field of precariously balanced rocks pbrs is located less than 1 km from the surface rupture trace of this holocene active normal fault ground motion prediction equations gmpes predict peak ground accelerations pgas of 0 2 0 3 g for the 1950 rupture and 0 3 0 5 g for the 5 6 ka paleoearthquake one kilometer from the fault surface trace yet field tests indicate that the fort sage pbrs will be toppled by pgas between 0 1 0 3 g we discuss the paleoseismic history of the fort sage fault in the context of the nearby pbrs gmpes and probabilistic seismic hazard maps for extensional regimes if the fort sage pbrs are older than the mid holocene rupture on the fort sage fault zone this implies that current gmpes may overestimate near fault footwall ground motions at this site

evolution of colpan barrier and lagoon complex lake van turkey sedimentological and hydrological approach abstract the northeastern coast of the lake van eastern anatolia turkey is exposed to energetic waves inducing large sediment transport rates intense wave activity on coastal environment shows the shaping impact on the shoreline either erosional or depositional processes sedimentation is characterized by gravelly beaches spit formation and barrier lagoon complex colpan barrier and lagoon complex forming the subject of this study occurred in these swashed environmental conditions this study aims to introduce formation and evolution of the colpan barrier and lagoon complex and to assess the future development of the coastal area around the lake van characteristics of barrier sediments as shape size provenance sedimentary structures and palaeocurrent directions are determined with field investigations smooth flattened and rounded polygenetic sediments compose the barrier drifted to the shoreline with coastal processes as wave and longshore currents colpan barrier was created a lagoon completely isolated from lake van this wetland constitutes a habitat for some animals and plants with relatively dilute water than sodic lake van s water level fluctuation is an important element for the constructive and destructive processes for the barrier and lagoon complex

slip rate variations on faults in the basin and range province caused by regression of late pleistocene lake bonneville and lake lahontan late pleistocene regression of two large pluvial lakes lake bonneville and lake lahontan caused considerable lithospheric rebound in the basin and range province usa here we use finite element models to show how lake growth and regression affect the temporal and spatial slip evolution on faults near the former lakes our results show that fluctuations in the volume of lake bonneville caused along strike slip variations on the wasatch normal fault with a pronounced slip rate increase on its northern and central parts during lake regression the response of normal and strike slip faults near the ring shaped lake lahontan depends on their location within the rebound area faults located in the centre of rebound show a slip rate increase during lake regression whereas strike slip faults at the periphery decelerate all slip rate variations are caused by differential stress changes owing to changing lake levels regardless of the individual fault response

differential effects of base level tectonic setting and climatic change on quaternary alluvial fans in the northern great basin nevada usa

mean dynamic topography intercomparisons and errors knowledge of the height of the sea surface above the geoid would allow one to determine the associated geostrophic surface currents and help to quantify subsurface currents and heat transports that regulate the earth s climate such a determination is presently hampered by our inability to accurately measure the geoid especially over the open ocean in anticipation of a future mean dynamic topography mdt provided by combining altimetry and a goce geoid this paper compares the mdts of several ocean models in the important north atlantic and nordic seas region focus area of the eu gocina project each of the models used in this study assimilates hydrography which is an essential requirement for a model to accurately interpolate the data and provide a realistic mdt the available mdts differ in resolution and time period both these issues are addressed a composite mdt is formed from the individual mdts and we assess the uncertainty in the composite mdt and in the associated geostrophic surface currents we find a remarkable level of agreement between this suite of model mdts the uncertainty in the composite mdt is less than 4cm over most of the study region and the uncertainty in the associated geostrophic surface velocities is of the order 2cm s these uncertainties can be used as error estimates when comparing with satellite derived mdts to judge consistency

drainage organization on the newly emerged dead sea bed israel abstract the organization of distributary drainage systems on the emerging coastal areas of the dead sea was studied following a rapid base level fall of 24 m during the period 1945 2002 which made the emerging pristine coastal zone a natural field laboratory photogrammetric digital elevation models were extracted to identify different emerged areas and to quantify erosion and deposition processes visual interpretation of orthophotos was used in order to recognize different drainage networks and to delineate the receding shoreline the remotely sensed data were backed by field surveys including measurement of longitudinal profiles the study demonstrates the spatial variability of runoff allocation from prograding fans to the emerging areas and the variable drainage responses three distinct environments were revealed on the emerged areas from the coast to the land deeply incised channels which are the main transmitters of the base level effect headward dendritic coalescing systems that are the reversal of the diverging channel system on alluvial fans and areas with unconfined sheet flowouts which are detached from base level control the threshold gradient of erosion on the emerged areas is 3 headward erosion was uncoupled with the lake level drop i e the rate of headward entrenchment increased with time despite an almost constant base level fall

geochronology and paleoenvironment of pluvial harper lake mojave desert california usa abstract accurate reconstruction of the paleo mojave river and pluvial lake harper manix cronese and mojave system of southern california is critical to understanding paleoclimate and the north american polar jet stream position over the last 500 ka previous studies inferred a polar jet stream south of 35 n at 18 ka and at 40 n at 17 14 ka highstand sediments of harper lake the upstream most pluvial lake along the mojave river have yielded uncalibrated radiocarbon ages ranging from 24 000 to 30 000 14 c yr bp based on geologic mapping radiocarbon and optically stimulated luminescence dating we infer a 45 40 ka age for the harper lake highstand sediments combining the harper lake highstand with other great basin pluvial lake spring and marine climate records we infer that the north american polar jet stream was south of 35 n about 45 40 ka but shifted to 40 n by 35 ka ostracodes limnocythere ceriotuberosa from harper lake highstand sediments are consistent with an alkaline lake environment that received seasonal inflow from the mojave river thus confirming the lake was fed by the mojave river the 45 40 ka highstand at harper lake coincides with a shallowing interval at downstream lake manix

application of uav photography to refining the slip rate on the pyramid lake fault zone nevada the pyramid lake fault zone plfz is a 50 km long active northwest trending right lateral fault in the northern walker lane located 30 km east of reno nevada previous paleoearthquake and slip rate studies report that the pyramid lake fault has produced four surface rupturing paleoearthquakes since 15 475 720 cal b p three of which occurred after 8980 260 cal b p and has had an average minimum slip rate of 2 6 0 3 mm yr since the late pleistocene these observations imply that coseismic offset for each paleoearthquake averaged 7 9 m larger than expected from empirical scaling relationships for a strike slip fault of its length to reconcile this discrepancy we used a small camera mounted unmanned aerial vehicle to develop high resolution digital elevation models and interpret previously unreported right laterally offset geomorphic features along the northern section of the plfz offset measurements at seven sites range from 8 to 21 m the ages of displaced features are interpreted from previous lake level and mapping studies of lake lahontan from these observations slip rate estimates at the sites range between 0 5 and 1 6 mm yr these lower values of slip rate require that coseismic displacements associated with previously reported paleoearthquakes average only 3 5 m within the range that would be predicted from empirical scaling relationships of rupture length and coseismic displacement

crustal strength in central tibet determined from holocene shoreline deflection around siling co abstract controversial end member models for the growth and evolution of the tibetan plateau demand quantitative constraints of the lithospheric rheology direct determinations of bulk crustal rheology however remain relatively sparse here we use the flexural rebound of lacustrine shorelines developed during the lingtong highstand around siling co in central tibet to place bounds on the effective elastic thickness t e and viscosity of tibetan crust shoreline features associated with the lingtong highstand complex 60 m above present lake level are deflected from horizontal by 2 4 m over wavelengths of 200 km optically stimulated luminescence dating of aggradational shoreline deposits indicates that these lake levels were reached at 6 4 ka assuming that surface loads were entirely supported by an elastic layer overlying an inviscid fluid the range and spatial distribution of variations in shoreline elevation are consistent with deflections predicted by a uniform elastic plate with thickness t e of 20 30 km if viscoelastic relaxation in response to lake withdrawal is complete our data suggest an average viscosity 10 19 pa s these results imply that the apparent viscosity of the lower crust inferred over millennial timescales is comparable with that estimated from post seismic relaxation over decadal timescale

estimating palaeowind strength from beach deposits abstract the geological record of past wind conditions is well expressed in the coarse gravel cobble and boulder beach deposits of quaternary palaeolakes in the great basin of the western usa and elsewhere this paper describes a technique using the particle size distribution of beach deposits to reconstruct palaeowind conditions when the lakes were present the beach particle technique bpt is first developed using coarse beach deposits from the 1986 87 highstand of the great salt lake in utah combined with instrumental wind records from the same time period next the bpt is used to test the hypothesis that wind conditions were more severe than at present during the last highstand of lake lahontan 13 ka which only lasted a decade or two at most the largest 50 beach clasts were measured at nine beach sites located along the north west and south sides of antelope island in the great salt lake all of which formed in 1986 87 at these sites the largest clast sizes range from 10 to 28 cm b axis and fetch lengths range from 25 to 55 km nearshore wave height was calculated by assuming that the critical threshold velocity required to move the largest clasts represents a minimum estimate of the breaking wave velocity which is controlled by wave height shoaling transformations are undertaken to estimate deep water wave heights and ultimately wind velocity wind estimates for the nine sites using the bpt range from 6 5 to 17 4 m s 1 which is in reasonable agreement with the instrumental record from salt lake city airport the same technique was applied to eight late pleistocene beaches surrounding the carson sink sub basin of lake lahontan nevada using the bpt estimated winds for the eight sites range from 9 7 to 27 1 m s 1 the strongest winds were calculated for a cobble boulder beach with a fetch of 25 km instrumental wind records for the 1992 99 period indicate that wind events of 9 12 m s 1 are common and that the strongest significant wind event 9 m s 1 for 3 h reached an average velocity of 15 5 m s 1 based on this preliminary comparison it appears that the late pleistocene western great basin was a windier place than at present at least for a brief time