holocene landscape evolution and geoarcheology of low order streams in the rio grande basin san juan mountains colorado usa abstract this geoarcheological study investigates soil stratigraphy and geochronology of alluvial deposits to determine holocene landscape evolution within the hot creek la jara creek and alamosa river drainage basins in the san juan mountains of colorado geomorphic mapping and radiocarbon dating indicate synchronicity in patterns of erosion deposition and stability between drainage basins in all three basins the maximum age of mapped alluvial terraces and fans is 3300 cal yr bp a depositional period seen at both hot creek and the alamosa river begins 3300 to 3200 cal yr bp based on soil development short periods of stability followed by alluvial fan aggradation occur in the alamosa river basin 2200 cal yr bp a period of landscape stability at hot creek before 1100 cal yr bp is followed by a period of rapid aggradation within all three drainages between 1100 and 850 cal yr bp a final aggradation event occurred between 630 and 520 cal yr bp at la jara creek these patterns of landscape evolution over the past 3300 yr provide the framework for an archeological model that predicts the potential for buried and surficial cultural materials in the research area

an 15 000 year record of el nino driven alluviation in southwestern ecuador debris flows have deposited inorganic laminae in an alpine lake that is 75 kilometers east of the pacific ocean in ecuador these storm induced events were dated by radiocarbon and the age of laminae that are less than 200 years old matches the historic record of el nino events from about 15 000 to about 7000 calendar years before the present the periodicity of clastic deposition is greater than or equal to 15 years thereafter there is a progressive increase in frequency to periodicities of 2 to 8 5 years this is the modern el nino periodicity which was established about 5000 calendar years before the present this may reflect the onset of a steeper zonal sea surface temperature gradient which was driven by enhanced trade winds

comparison of site specific and empirical correlations for drained residual shear strength analyses of landslides slopes and embankments often require reliable drained residual shear strength estimates for cohesive deposits involving pre existing shear surfaces laboratory tests to meas

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

a correlation between residual friction angle gradation and the index properties of cohesive soils this technical note proposes a new correlation between residual friction angle gradation and the index properties of cohesive soils the proposed correlation was obtained on the basis of laboratory tests performed on more than 20 sites along the autostrade spa motorway network in italy the test specimens were taken mostly from samples obtained from borings and test pits in the apennine silty clayey soils direct shear and ring shear tests were used to determine the residual shear strength the proposed correlation gives reliable qualitative indications when the input data for design cannot be obtained from an extensive laboratory test programme it has been included in a multi function database which contains all the available technical information required to design remedial measures in landslide areas trrl

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

river terrace systems in north west europe an archive of environmental change uplift and early human occupation abstract staircases of large scale aggradational river terraces are a notable feature of many valleys in the temperate lattitudes particularly in areas beyond the reach of the erosive activities of pleistocene ice sheets it is now recognized that the cyclic fluctuations of climate during the quaternary have driven the generation of terraces through the direct and indirect influence of both temperature and precipitation on fluviatile activity where fossiliferous deposits are preserved within terrace sequences it is often possible to date these and to correlate them with the oceanic record thus providing an important framework for the evidence of environmental change on land middle and late pleistocene terraces in different areas can commonly be seen to have formed in synchrony with glacial interglacial cycles or with longer periodicity megacycles climatic forcing alone is insufficient to cause terraces to form however uplift is also necessary so that terrace sequences can provide a useful record of crustal movement in northwest europe where some of the best known studies of river terrace sequences have been carried out the fluviatile deposits are also an important repository for palaeolithic artefacts from which a record of early human occupation can be reconstructed

lower timberline in central colorado during the past 15 000 yr a 15 000 yr paleoenvironmental record at the elevation of lower timberline in central colorado suggests two major paleoclimatic changes during that interval 1 at 10 000 yr b p from cool moist conditions to warm moist conditions and 2 at 4 000 yr b p to warm dry conditions this sequence can be interpreted as a shift from precipitation predominantly originating from pacific winter storms before 10 000 yr b p to a predominantly monsoonal type regime lasting until 4 000 yr b p to the present pattern contemporaneity of higher upper timberline and lower lower timberline during the 10 000 to 4 000 yr b p interval is not contradictory but a result of changes in those circulation patterns

chronology of pleistocene glacial advances in the central rocky mountains the distribution and ages of moraines in the wyoming type localities for pre pinedale rocky mountain glacial deposits are not well known through morphostratigraphic mapping river terrace longitudinal profile analysis and tephrochronology we place the age of sacagawea ridge moraines in the dinwoody lakes type area at about 660 ka outwash and river terrace deposits in the bull lake type area previously considered to be sacagawea ridge are actually older by one or two glacial cycles in the bull lake type locality 15 individual moraines are divided into 4 groups on the basis of relative age criteria using 36cl 10be cosmogenic dating of boulders the two older groups must be 130 ka the younger groups are given age ranges of 130 to 100 ka and 120 to 95 ka a terrace along wind river can be morphostratigraphically traced to the youngest of these moraine groups 36cl dating of boulders on the terrace provides an age range of 125 to 100 ka the combined relative age and cosmogenic nuclide chronology is consistent with previously published evidence from yellowstone national park demonstrating that mountain glaciers advanced not only prior to and during the later portion of marine isotope stage 6 but also during marine isotope stage 5d in contrast with some other areas of the rocky mountains we found no evidence for advances during marine isotope stage 4 at bull lake pinedale moraines that have a 36cl 10be age range of 23 to 16 ka suggest that glacial advances were limited to the later part of marine isotope stage 2 a river terrace that can be traced to these moraines has an age range of 23 to 16 ka a possible glacial advance during early marine isotope stage 2 is indicated by a river terrace whose age range is estimated by incision rate modeling at 46 to 28 ka but no moraines were identified along wind river there are eight terrace levels capped with outwash that are older than sacagawea ridge although the terraces are the record of early to middle pleistocene climatic cycles there are no correlative moraines preserved at the land surface

drained residual shear strength at effective normal stresses relevant to soil slope stability analyses abstract an extensive torsional ring shear testing program has been conducted to measure the drained residual shear strength of soils at the wide range of effective normal stress 10 to 700 kpa usually mobilized in reactivated and first time landslides soils mudstones and shales of different plasticity and gradation were tested in the program the effects of the change in nonlinearity of shear strength envelope over the utilized normal stress ranges on slope stability analyses were investigated using this data new empirical residual shear strength correlations were developed as a function of soil index parameters and wide range of effective normal stresses in essence the correlations are presented as revised versions of those previously developed for a limited number of normal stresses utilizing the same soil index parameters comparisons were made with a considerable amount of back calculated shear strength data reported in the literature for reactivated landslides as well as results predicted from existing shear strength correlations to verify the increased suitability of the new correlations for use in slope stability analyses a numerical expression was also introduced to express the residual shear strength correlations for direct incorporation in slope stability software

post glacial range of variability in the conejos river valley southern colorado usa fluvial response to climate change and sediment supply effective river management strategies require an understanding of how fluvial processes vary both spatially and temporally here we examine the natural range of variability in the conejos river valley southern colorado through documentation of terrace morphostratigraphic and sedimentological characteristics as well as through investigation of sediment contributions from headwaters hillslopes and tributary streams additionally soil development and radiocarbon ages together with local and regional paleoclimate reconstructions were used to infer the range of processes acting in this system since de glaciation the conejos river has fluctuated between episodes of bedrock strath formation aggradation and vertical incision morphostratigraphic relationships soil development and radiocarbon ages enable us to propose a chronology for periods of alluvial deposition around 8 9 7 6 ka 5 5 ka and from 3 5 to 1 1 ka separated by intervals of fluvial incision we infer potential forcing mechanisms by utilizing multiple working hypotheses specifically we discuss the potential for increases in sediment supply during periods of 1 para glacial adjustment 2 climatic cooling 3 increased frequency of climate change and 4 increased fire frequency or severity we also consider the effects of changes in stream discharge and extreme storm occurrence we conclude that combinations of these processes operating at different times have contributed to sediment mobilization since de glaciation stream and landform morphology also varies longitudinally due to the influence of remnant glacial topography in particular valley bottom overdeepening at tributary junctions has resulted in incision and strath formation into unlithified glacial deposits i e fill cut terraces rather than bedrock in some reaches overall the conejos fluvial system has varied significantly both temporally and spatially since de glaciation and appears to be sensitive to changes in sediment supply related to holocene scale climate fluctuations this natural range of variability must therefore be a key consideration in any future stream management policies copyright 2012 john wiley sons ltd

numerical simulations of glacial valley longitudinal profile evolution glaciers shape alpine landscapes they broaden valley bottoms enhance local valley relief generate multiple steps overdeepen valley floors and cause tributary valleys to hang these distinctive glacial signatures result from 10 4 10 5 yr of erosion during which swings in climate drive advances and retreats of alpine glaciers we use a numerical model of glacial erosion to explore the development of the longitudinal profiles of glaciated valleys the model is driven by the past 400 k y of variable climate because both sliding speed which dictates abrasion rate and water pressure fluctuations which strongly modulate quarrying rate should peak at the equilibrium line altitude ela we expect the locus of most rapid erosion to follow the transient ela simulations of a single glacial valley show rapid flattening of the longitudinal profile inclusion of a tributary glacier creates a step immediately downvalley of the tributary junction that persists over multiple glaciations and commonly leaves the tributary valley hanging steps and overdeepenings result from an increase in ice discharge immediately below the tributary junction which is accommodated primarily by increased ice thickness and hence sliding rate the size of the step increases with the ratio of tributary to trunk ice discharge while the height of a hanging valley reflects the difference in the time integrated ice discharge in tributary and trunk valleys and therefore increases as the discharge ratio decreases

timberline fluctuations and late quaternary paleoclimates in the southern rocky mountains colorado pollen and plant macrofossils from eight sedimentary basins on the west slope of the colorado rocky mountains document fluctuations in upper and lower timberline since the latest pleistocene by tracking climatically sensitive forest boundaries the moisture controlled lower timberline and the temperature controlled upper timberline paleoclimatic estimates can be derived from modern temperature and precipitation lapse rates pollen data suggest that prior to 11 000 yr b p a subalpine forest dominated by picea spruce and pinus pine grew 300 700 m below its modern limit the inferred climate was 2 5 c cooler and had 7 16 cm greater precipitation than today abies fir increased in abundance in the subalpine forest around 11 000 yr b p probably in response to cooler conditions with increased winter snow pollen and plant macrofossil data demonstrate that from 9000 to 4000 yr b p the subalpine forest occupied a greater elevational range than it does today upper timberline was 270 m above its modern limit suggesting that mean annual and mean july temperatures were 1 2 c warmer than today intensification of the summer monsoon coupled with increased summer radiation between 9000 and 6000 yr b p raised mean annual precipitation by 8 11 cm and allowed the lower limit of the subalpine and montane forests to descend to lower elevations the lower forest border began to retreat upslope between 6000 and 4000 yr b p in response to drier conditions and the upper timberline descended after 4000 yr b p when temperatures cooled to about 1 c warmer than today the modern climatic regime was established about 2000 yr b p when the summer precipitation maxima of the early and middle holocene were balanced by increased winter precipitation

post glacial fluvial response and landform development in the upper muskegon river valley in north central lower michigan u s a article i nfo this study focuses on the upper part of the muskegon river system in north central lower michigan and is the first to reconstruct the post glacial history of fluvial landform development in the core of north america s great lakes region results indicate that the upper muskegon river valley contains four alluvial terraces and numerous paleomeanders radiocarbon dating of peats within these old channels provides a good chronology for stream behavior and landform development the t 4 terrace is a paired pleistocene outwash lacustrine surface that probably formed about 12 500 years ago the t 3 terrace is a fill strath surface that was cut between about 12 000 and perhaps 9500 years ago the geometry of macromeanders on this surface suggests that stream discharge was 8 times greater than during the holocene the pleistocene holocene transition is marked by a major period of downcutting that likely began as the climate warmed dried and sediment yield diminished this period of downcutting potentially lasted through the drier middle holocene creating a 6 m high escarpment in the valley the muskegon river then began to aggrade when the climate became wetter subsequently the river again incised creating the paired t 2 terrace about 3400 years ago when the climate became still wetter t 2 paleomeanders indicate that stream discharge at this time was consistent with the modern river in the past 2500 years the stream has constructed a poorly defined complex of t 1 terraces these surfaces likely formed due to complex response associated with more variable climate this study demonstrates that the upper muskegon river has a similar post glacial history as streams on deglacial and periglacial landscapes elsewhere in the world

pacing the post last glacial maximum demise of the animas valley glacier and the san juan mountain ice cap colorado during the last glacial maximum lgm a 5000 km 2 ice cap covered the san juan mountains of southwest colorado the largest valley glacier draining this ice cap occupied the animas valley and flowed 91 km to the south to characterize the post lgm demise of the animas valley glacier we employ cosmogenic 10 be to date the lgm terrace outside the terminal moraines and a suite of seven glacially polished bedrock samples the 10 be depth profile within the terrace sediments suggests abandonment at 19 4 1 5 ka as deglaciation began the ponding of glacial lake durango behind the terminal moraines shut off fluvial sediment supply and caused terrace abandonment the age of the terrace therefore records the initiation of lgm retreat negligible 10 be inheritance in the terrace profile suggests that glacial erosion of the bedrock valley floor from which sediments were derived erased all cosmogenic inventory glacial polish exposure ages monotonically decrease up valley from 17 1 to 12 3 ka with the single exception of a sample collected from a quartzite rib yielding an average retreat rate of 15 4 m yr this trend and the lack of inherited cosmogenic nuclides in the terrace sediments imply that polish ages accurately record the glacial retreat history retreat of the animas lobe began at a time of regional drying recorded in sediments and shoreline elevations of large lakes deglaciation lasted for 7 2 k y and was complete by 12 3 1 0 ka the retreat history followed the pattern of increasing insolation and was perhaps fastest during a time of regional drying

a comparison and integration of tree ring and alluvial records of fire history at the missionary ridge fire durango colorado usa we used tree ring and alluvial sediment methods to reconstruct past fire regimes for a mixed conifer forest within a 1 km2 drainage basin which was severely burned by a wildfire near durango color

15 k y paleoclimatic and glacial record from northern new mexico the southern sangre de cristo mountains new mexico contain evidence of glacial activity from the late pleistocene to late holocene sediment cores recovered from an alpine bog 3100 m trapped behind a pinedale age moraine 2 km downvalley from a high elevation cirque reached glacial age debris and recovered 6 m of lake clays overlain by gyttja accelerator mass spectrometry dating sedimentology variations in magnetic properties and organic carbon data reveal six distinct periods of glacial and or periglacial activity these include a late pleistocene pinedale glacial termination just before 12120 1 4 c yr b p a younger dryas chron cirque glaciation an early neoglacial periglacial event ca 4900 1 4 c yr b p a late holocene cirque glaciation 3700 1 4 c yr b p as well as late holocene periglacial events at 2800 1 4 c yr b p and the little ice age ca 120 1 4 c yr b p cold events in the middle to late holocene correlate with subtle ice rafting events in the north atlantic and records of cold events in north america and europe and were probably hemispheric in extent

properties and microstructure of a natural slip zone in loose deposits of red beds southwestern china abstract the loose deposits of red beds located in southwestern china are vulnerable to the occurrence of landslides in this paper a shallow progressive landslide developed in loose deposits of red beds was selected as a case study and the physical and mechanical properties of the main slip zone were analyzed in detail it was observed that the main slip zone of the progressive landslide is composed of fine grained soils with substantial amounts of expansive clay particles interlayered illite smectite and interlayered chlorite smectite the one dimensional consolidation test of the residual soils shows that the soils are overconsolidated the shear stress versus shear displacement curves reveal that the slip zone soil has exhibited a strain softening behavior the residual friction angle of the undisturbed slip zone soil determined by the ring shear tests is 7 2 indicating that the residual strength of the soil is very low when in a saturated state the microstructure of the slip zone was investigated using a combination of images captured by means of polarising microscopy pm and scanning electron microscope sem techniques it was found that the slip zone possessed generally softer structure with higher relative porosities than its confining materials the microstructure of the slip zone is generally characterized by its softer structure and higher degree of alignment of fine silts suggesting that the slip zone underwent two deformation processes i e dilatancy and particle rearrangement the global mechanical behavior of the investigated slip zone may be conceptualized as an overconsolidated clayey soil under drained conditions

residual strength of clays and correlations using atterberg limits various attempts have been made to correlate the residual strength friction angle of soils to their index parameters either the particle size or the atterberg limits the first correlation attempt was that of skempton 1964 relating the residual strength friction angle to clay fraction followed by a number of others the best known probably being lupini et al 1981 mesri and cepe da diaz 1986 colotta et al 1989 and stark et al 1994 the purpose of this paper is to reconsider these correlation attempts and to make some general comments about the use of atterberg limits for correlation purposes a

chronosequence development and soil variability from a variety of sub alpine post glacial landforms and deposits in the southeastern san juan mountains of colorado abstract surficial processes acting on post glacial alpine and sub alpine landscapes vary at small temporal and spatial scales and are thus often difficult to conceptualize in the context of large scale landscape evolution models soils developing in this setting can thus provide valuable information about landform genesis sedimentology and age relatively few post glacial chronosequences have been examined in these settings however particularly for the variety of landforms and parent materials that exist within alpine and sub alpine environments here we examine a chronosequence of relatively young post glacial landforms with varying parent materials and climate histories we dug and described 39 soil pits in the upper conejos river valley of colorado on a variety of deposits and landforms including alluvial fans terraces colluvium glacial till and terminal moraines and compared soil properties with radiocarbon ages from the area our results suggest that some typical chronosequence soil properties e g ph structure color do not correlate with time over short time scales however extractable iron ratios feo fed show a relatively strong correlation with age across late pleistocene and holocene time scales and maximum profile clay content shows a weak but statistically significant relationship with age both of these trends are stronger when examined across a single parent material differences in initial parent material texture and dust inputs seem to be the most significant complicating factors over post glacial time scales soil property development through time is most inconsistent in cumulic alluvial fan soils this observation may indicate that alluvial fans are more responsive to sub basin scale processes as opposed to fluvial terraces that are more likely respond to processes active across the entire basin these differences would explain why stratigraphically similar alluvial fans are mantled by soils with varying development nonetheless horizonation clay content and extractable iron ratios provide a useful tool for correlating young deposits assigning ages and interpreting the geomorphic history of complex post glacial environments

a new method for the correlation of residual shear strength of the soil with mineralogical composition mineralogical composition measured with x ray diffraction for soil specimens collected from more than 80 natural disaster areas show smectite kaolinite mica feldspar and quartz as major constituent minerals based on the results of more than 35 mixtures of smectite kaolinite and quartz in different proportions a new correlation method was proposed for estimation of the residual friction angle r with the proportion of the minerals the mineralogical compositions of the natural samples were used to estimate the r based on the proposed triangular model the estimation method resulted in values as close as 90 to the measured r and as close as 80 to the case of 53 samples tested by other researchers the paper incorporates the correlation of r with the liquid limit the plasticity index the clay fraction the specific surface area and the proportion of smectite various ranges are proposed according to the influence of the constituent clay minerals in addition the applicable range

a chronology of post glacial landslides suggests that slight increases in precipitation could trigger a disproportionate geomorphic response large deep seated landslides are common throughout the southeastern san juan mountains of colorado and new mexico but their timing and initiation are not well understood determining when the landslides occurred would aid in clarifying the mechanisms for initiating landslides in the region and would help us to understand post glacial landscape evolution we studied seven prehistoric landslides located within the tertiary volcanic rocks of the san juan volcanic field the landslides range in area from 0 8 km2 to 11 3 km2 and most are located in areas that were previously mapped as having been ice covered during the last glaciation landslide deposits were dated using a variety of methods including surface exposure dating 36cl radiocarbon dating of basal bog sediments and organic material buried in soils and relative soil development the resulting limiting ages range from approximately 14 ka to 2 ka and show that deep seated landsliding has occurred throughout the post glacial period this broad range in ages is inconsistent with our initial hypothesis which proposed that landslides were likely the result of debuttressing of glacial walls during glacial retreat furthermore the timing of landslides does not seem to correlate with documented post glacial climatic shifts therefore we conclude that landsliding in the region was the result of wetter than normal periods lasting months to years acting on weak bedrock pre conditioned to failure and prepared by glacial debuttressing our findings suggest that the study area is likely still susceptible to deep seated landsliding and may become even more prone to large scale slope failure if future climate change increases precipitation in the san juan mountains

late quaternary fluvial terraces of the romagna and marche apennines italy climatic lithologic and tectonic controls on terrace genesis in an active orogen abstract we synthesize a new fluvial terrace chronostratigraphy of the bidente and musone rivers cast within a broader european framework which forms the basis of a terrace genesis and river incision model for the northern apennines italy our model supported by terrace long profiles correlation to po foreland sediments 15 new radiocarbon dates and published numeric and relative stratigraphic ages highlights how drainage basin substrate drives concurrent formation of strath terraces in the bidente basin and fill terraces in the musone basin quaternary climate change paces the formative geomorphic processes through unsteady discharges of water and sediment in the weathering limited setting represented by the bidente basin siliciclastic detritus carves broad strath surfaces during glacial climates that are preserved as terraces as the river incises during the transition to an interglacial climate in contrast the transport limited and carbonate detritus dominated musone basin sees valleys deeply buried by aggradation during glacial climates followed by river incision during the transition to an interglacial climate incision of these rivers over the past 1 million years has been both unsteady and non uniform these and all po adriatic draining rivers are proximal to a base level defined by mean sea level and have little room for increasing their longitudinal profile concavities through incision particularly in their lower reaches despite periodic glacio eustatic drawdowns as a result the observed incision is best explained by rock uplift associated with active local fault or fold growth embedded in the actively thickening and uplifting apennine foreland

holocene strath terraces climate change and active tectonics the clearwater river basin olympic peninsula washington state the 400 km 2 clearwater river basin located on the pacific flank of the actively uplifting olympic mountains of western washington state contains a well preserved flight of holocene fluvial terraces we have collected a large data set of numeric ages from these terraces that is used to elucidate the geomorphic fluvial active tectonic and climatic processes that operate at holocene spatial and temporal scales detailed field mapping reveals three prominent holocene straths and their overlying terrace deposits terrace ages fall into three broad ranges ca 9000 11 000 yr b p qt4 4000 8000 yr b p qt5 and 0 3000 yr b p qt6 terrace deposit stratigraphy sedimentology and age distributions allow us to consider two alternative models for their genesis the favored model states that the terrace ages are coincident with lateral incision of the clearwater channel emplacement of the terrace alluvium and the carving of the straths vertical incision of the clearwater channel was primarily relegated to the brief 1000 yr intervals when we have no record of terraces alternatively the straths were carved as the channel incised vertically during the brief time periods between dated terrace deposits and the terrace ages record a subsequent long time of alluviation atop the straths and concomitant termination of vertical incision in both models we envision a clearwater river channel at or near capacity with a temporally variable rate of both lateral and vertical incision small deviations from this at capacity condition are driven by variations in the liberation and delivery of hillslope sediment to the channel we consider several causes for variable hillslope sediment flux in this tectonically active setting including holocene climate change and ground accelerations related to earthquakes holocene rates of vertical incision are reconstructed along nearly the entire clearwater valley from the wide distribution of dated terraces incision rates clearly increase upstream mimicking a pattern documented for pleistocene terraces in the same basin however the rates are 2 3 times those determined for the pleistocene terraces the faster holocene incision rates may be interpreted in terms of an increase in the rates of rock uplift however we favor an alternative explanation in which the holocene rates represent a channel rapidly reacquiring its stable graded concavity following protracted periods of time in the pleistocene when it could not accomplish any vertical incision into tectonically uplifted bedrock because the channel was raised above the bedrock valley bottom by climatically induced alluviation these results illustrate how even in tectonically active settings representative rates of rock uplift inferred from studies of river incision should be integrated over at least one glacial interglacial cycle

spatial and temporal variation of sediment processes in the alpine semi arid basin of alkali creek colorado usa this paper develops a simple method of predicting sediment removal during snowmelt and flashfloods in alkali creek watershed western colorado the method links successful runoff simulations to field monitored sediment relationships to predict site yield the yield data are differenced to derive an index of scour and fill from which it is possible to infer the patterns of erosion and deposition that the stimulated events might produce across the watershed site sediment yield patterns produced suggest that even for a basin with this south facing orientation the summer storms are geomorphologically ineffective when compared to the amount of sediment transport potentially associated with the melt flows from a stimulated snowpack predicted patterns of scour and fill are spatially and temporally variable and are dependent on sediment supply laterally to the network scour is extensive at tributary junctions explaining the overall network concavity these patterns conform generally with monitored channel change in the network over a 13 year period and can be contrasted with patterns of sediment yield documented for other climatic types it is concluded that in this alpine semi arid environment the sediment rich debris removal associated with the decay of a considerable snowpack in the spring months is the most important geomorphic process and that tributary junctions appear likely to be the most active sites of change implications for threshold behaviour in these environments are also explored

roll and cell convection in wintertime arctic cold air outbreaks abstract cold air outbreaks from the polar ice caps or winterly continents over the open ocean lead to organized convection that typically starts as longitudinal roll patterns and changes to cellular patterns in downstream direction during the field experiments arktis 1991 and arktis 1993 aircraft missions were conducted in 13 cold air outbreak events over the greenland and barents seas to determine the characteristic parameters of both the mean primary flow and the superimposed organized convection secondary flow the measurements are classified into four categories with respect to the convective pattern form longitudinal rolls with small and wider horizontal wavelengths transitional forms between rolls and cells and cells rolls were observed for boundary layer depths h 1 4 km with 8 km and h between 4 and 12 the amplitudes of the secondary flow scale varia

a 900 k y record of strath terrace formation during glacial interglacial transitions in northwest china the timing of the development of strath terraces with respect to climatic variability remains equivocal previous studies attribute strath terrace formation to glacial or interglacial climates or to variations in sediment and water fluxes that cause lateral erosion followed by vertical incision a chronology of strath terrace formation spanning similar to900 k y has been generated on the basis of loess paleosol couplets and paleomagnetic thermoluminescence and radiocarbon dating of strath terraces in the qilian shan of northeastern tibet repetitive stratigraphic and geomorphic patterns on each terrace indicate that they formed during glacial interglacial transitions long term bedrock incision rates and inferred rock uplift rates appear steady and unrelated to strath formation over the past 900 k y

effective attenuation lengths of cosmic rays producing 10be and 26al in quartz implications for exposure age dating we have measured cosmic ray produced 10be t 1 5 my and 26al t 0 72 my as functions of depth in a core of quartz sandstone bedrock collected in south victoria land antarctica these data were used to place limits on the exposure age and erosion rate of the exposed surface and to calculate the effective attenuation lengths of cosmic rays producing these nuclides these latter results indicate that the production attenuation length for 26al is comparable to that for 10be this suggests that the production ratio 26al 10be does not vary substantially with depth in a rock and that its value at the surface of exposed rock is not strongly affected by erosional losses allowing wider use of the ratio in determining exposure ages

stream incision and terrace development in frijoles canyon bandelier national monument new mexico and the influence of lithology and climate abstract the record of stream incision and terrace development in frijoles canyon nm was investigated to examine the controls on channel evolution in this region frijoles canyon developed after deposition of the voluminous ignimbrites of the tshirege member of the bandelier tuff at ca 1 22 ma which provides excellent temporal constraints on canyon evolution base level fall along the rio grande the master drainage in the region contributed to initial incision of the stream development of a major knickpoint in basalt near the rio grande however has effectively isolated most of the stream channel from direct effects of this base level change since the early or middle pleistocene late quaternary evolution of the channel has included development of strath and fill terraces that record the effects of climatic variations and local lithologic variations within the tuff on channel processes a fill terrace underlain by up to 13 m of coarse gravelly alluvium records significant aggradation in the early to middle holocene following a major regional climate change aggradation probably resulted from large increases in sediment supply in the holocene relative to the late pleistocene which was perhaps related to variations in intense summer rains rapid incision in the middle to late holocene has stranded the underlying strath up to 21 m above the modern channel and local rates of incision of up to 4 m ka are more than 10 times the average rates since 1 22 ma holocene incision displays great spatial variability associated with local lithologic variations and results in a stream profile that has evolved rapidly in the last 10 000 years the high rates of incision occur where easily eroded nonwelded tuff is exposed in the canyon bottom whereas a more resistant vapor phase altered tuff unit upstream has impeded incision incision may also have been affected by migration of knickpoints within the tuff paired strath terraces record periods of local base level stability and lateral erosion that were terminated by episodes of downcutting the downcutting was probably controlled by rare high magnitude floods capable of stripping the pervasive gravel armor and exposing nonwelded tuff beneath the stream bed no tectonic influence on late quaternary terrace development or stream incision has been recognized despite frijoles canyon being crossed by the pajarito fault zone a major bounding structure of the rio grande rift instead climatic influences on sediment supply and flood characteristics mediated by lithologic variations in the canyon bottom have controlled late quaternary stream profile evolution

temperature dependent residual shear strength characteristics of smectite bearing landslide soils this paper presents experimental investigations regarding the effect of temperature on the residual strength of landslide soils at slow to moderate shearing velocities we performed ring shear tests on 23 soil samples at temperatures of 6 29 c the test results show that the shear strength of smectite rich soils decreased when temperatures were relatively low these positive temperature effects strength losses at lower temperatures observed for smectite bearing soils are typical under relatively slow shearing rates in contrast under relatively high shearing rates strength was gained as temperature decreased as rheological properties of smectite suspensions are sensitive to environmental factors such as temperature ph and dissolved ions we inferred that temperature dependent residual strengths of smectitic soils are also attributed to their specific rheological properties visual and sem observations of ca bentonite suggest that slickensided shear surfaces at slow shearing rates are very shiny and smooth whereas those at moderate shearing rates are not glossy and are slightly turbulent indicating that platy smectite particles are strongly orientated at slow velocities the positive temperature effect is probably due to temperature dependent micro friction that is mobilized in the parallel directions of the sheet structure of hydrous smectite particles on the contrary the influence of micro viscous resistance which appears in the vertical directions of the lamination is assumed to increase at faster velocities our results imply that if slip surface soils contain high fractions of smectite decreases in ground temperature can lead to lowered shear resistance of the slip surface and trigger slow landslide movement

correlation of mineralogy and index properties with residual strength of iraklion marls abstract the marly formations of the city of iraklion in crete greece are described and classified according to their mineralogy and physical properties the residual angle of friction of these marls was determined using ring shear apparatus and the results were correlated with mineral composition and index properties such as atterberg limits and grain size distribution furthermore for better understanding of the determined interrelationships between the physical characteristics and the residual strength of these marls a number of marl bentonite mixtures were also tested thus the influence of the variation in clay mineral content on the residual strength was studied and correlations with clay sized fraction and plasticity index were attempted

why rolls are prevalent in the hurricane boundary layer recent remote sensing observations show that the hurricane boundary layer flow although energetic is not a region of homogeneous turbulence in fact the observations convincingly demonstrate that a large fraction of the turbulent flow in the regions away from the deep convective rainbands is highly organized into intense horizontal roll vortices that are approximately aligned with the mean wind and span the depth of the boundary layer these observations show that rolls strongly increase the flux of momentum between the underlying surface and the main body of the storm compared to an equivalent hurricane boundary layer flow without rolls the linear and nonlinear dynamics of hurricane boundary layer roll formation are outlined and it is shown why rolls are in fact the expected basic hurricane boundary layer state the model presented here explains the hurricane roll features currently documented in field programs and makes predictions that can be tested in future experiments the primary effects of rolls on the boundary layer fluxes are inherently nonlocal and nongradient and hence cannot be captured by standard downgradient turbulence parameterizations used in hurricane simulations however the nonlinear theory is the proper starting point for developing boundary layer parameterizations that include roll modification of the turbulent fluxes

observations and numerical simulation of atmospheric cellular convection over mesoscale topography radar and satellite images provide observations of convective rolls and other structures in the convective boundary layer cbl but the data are intermittent and neither radar nor satellite gives a complete picture of roll circulation in the observed cases as a consequence numerical modeling is a useful complement to the observations to investigate the temporal and spatial details of convective rolls in this paper observations of convective rolls over the south of england are described numerical simulations have been performed to investigate these rolls using the boundary layer above stationary inhomogeneous uneven surfaces blasius model a relatively simple boundary layer code for flow over topography the numerical results indicate that most of the features of the convective structures can be successfully reproduced notably the roll orientation and spacing and the basic features of the cloud field these features are in good agreement for two case studies one with distinct rolls and the other with more dispersed convective structures and a time dependent basic state the model tends to predict the initial occurrence of rolls later than observed and this time of occurrence is found to be influenced by model resolution the presence of low topography with maximum height on the order of 30 of the cbl depth may have a small influence on the average orientation and spacing and the time of initial occurrence of modeled rolls local flow anomalies related to the hills are much more pronounced these anomalies appear to be related to coherent patterns in the model cloud fields with a tendency for more cloud cover upstream and over hills and cloud clearing in the lee as a result of descent suppressing convective eddies when the satellite imagery is combined with topography data this kind of orographic control of the shallow convection by the topography is evident the cbl height varies considerably in the early stages of cbl evolution over hilly topography but when the convection is fully developed the cbl height is almost constant over the domain

a high resolution record of climate vegetation and fire in the mixed conifer forest of northern colorado usa high resolution pollen charcoal 13c total organic carbon toc and magnetic susceptibility data from sediment cores from a montane lake in northern colorado record variations in vegetation fire history and sedimentation since 14 5 ka 1 ka 1000 cal yr b p this record shows warm conditions during the bolling allerod and the coldest conditions in this area during the younger dryas event warming occurred throughout the early and middle holocene lasting until ca 5 ka when the warmest and wettest summer conditions were recorded progressive climate cooling and enhanced winter precipitation are then observed until present day these long term climatic trends correlate to changes in summer insolation charcoal accumulation rates char increased along with the arboreal vegetation from minima in the late glacial period to maxima during the early and middle holocene suggesting that charcoal influx was also controlled by climate and vegetation toc and 13c show a progressive increase and a decrease trend during the late pleistocene and holocene respectively related to changes in vegetation and productivity in the lake major peaks in the char record correspond with peaks in magnetic susceptibility indicating enhanced fire induced erosion and sedimentation millennial and centennial scale changes are also observed throughout the different proxy records they exhibit strong correlations with climate records from distant regions including greenland and the north atlantic providing evidence for global teleconnections among regional climates a solar climate connection is suggested by prominent ca 225 and 390 yr cycles which may correlate with the 208 yr suess and 400 yr solar cycles

observations on the role of lithology in strath terrace formation and bedrock channel width field observations from western washington and eastern tibet indicate a strong lithologic influence on strath terrace formation and highlight the response of bedrock channel width to spatial gradients in bedrock erodibility and or rock uplift rates measurements of local bedrock bed and bank erosion rates together with observations of the role of weathering processes on erosion of siltstones and sandstones illustrate a mechanism that underlies a conceptual model that predicts a strong lithological control on strath terrace formation direct measurements of bedrock erosion rates in lithologies susceptible to accelerated erosion upon sub aerial exposure show that lateral rates of bedrock bank erosion can substantially exceed vertical incision below the perennial flow level due to an asymmetry in erodibility between perennially submerged rock and rock exposed to cyclic wetting and drying on bedrock channel walls under such conditions the rapid weathering mediated lowering of bedrock exposed above baseflow promotes development of a beveled bedrock platform that could become a strath terrace upon abandonment in contrast to previous studies channel widths measured across a substantial gradient in lithology slope and long term erosion rates in eastern tibet do not follow conventional relations where channel width scales as a power law function of drainage area instead as they flow across a zone of rapid uplift these channels systematically narrow relative to the predicted width extrapolated from traditional power law relations field studies from a wide range of geological settings and lithologies support the interpretation that in general strath terraces tend to be more extensive in rivers flowing over weak sedimentary rock and tend to be poorly developed and or preserved where rivers flow over hard erosion resistant rock

ancient hillslope deposits missing links in the study of climate controls on sedimentation rare outcrops of miocene pliocene buried hillslopes and colluvium present in proximal basin fill exposures in the arid southwestern united states in settings free of tectonic influences reveal hillslope sediment production and delivery to piedmonts that vary as a function of climate change a petrologic weathering index for sand clay mineral data and stratigraphic relations indicates that episodes of greater production and delivery of colluvium from hillslopes coincide with more intense chemical weathering and thus greater effective moisture strata recording limited colluviation less intense weathering and piedmonts dominated by eolian processes very likely correspond to drier conditions the mode of climate driven hillslope and piedmont landscape responses evident in these older stratigraphic records corroborates the conceptual model developed by quaternary researchers for arid environments even though climate change was operating at higher amplitudes and different frequencies in the quaternary this evidence of long term continuity in the mode of landscape response to climate change provides a new level of support for using the geologic record to understand the effects of future climate change

a high resolution simulation of convective roll clouds during a cold air outbreak 1 a ubiquitous feature of the high latitude ocean is the occurrence of convective clouds that are organized into two dimensional structures known as roll clouds or cloud streets in this paper we present a simulation of these structures that was performed in a domain large enough to simulate numerous roll clouds and their downstream evolution at a resolution sufficient to resolve the individual convective clouds the simulations were initialized and validated using observations of roll clouds over the labrador sea the model results indicate that the secondary flow associated with the roll clouds results in significant differences in the temperature humidity and momentum fields between the updrafts and downdrafts the model was also able to reproduce the observed downstream evolution of the clouds as the organization of the convection changed from two dimensional rolls to three dimensional closed cells

the effect of bedrock jointing on the formation of straths in the cache la poudre river drainage colorado front range the north fork poudre and poudre rivers have incised deep narrow canyons into precambrian age granite and gneiss along the colorado front range longitudinally discontinuous active strath surfaces and strath terraces are present along each river although the crystalline bedrock of the study area is resistant to weathering and erosion differences in joint spacing and orientation create significant differences in rock mass strength along each river the vertical spacing of active straths along the north fork poudre correlates strongly with the spacing of prominent subhorizontal joint surfaces strath terraces along the poudre river occur in areas of wider valley bottom upstream from a profile convexity especially wide segments with the greatest downstream extent reflect the locations of shear zones that create more densely spaced joints and lower rock resistance i interpret the absence of strath terraces in wider canyon segments downstream from the convexity to indicate that the poudre river is capable of laterally eroding the entire valley bottom as the river incises leaving behind only fill terraces upstream from the convexity in contrast lateral erosion has created canyon segments with wider valley bottoms but the entire valley bottom has not been lowered at the same rate leaving discontinuous strath terraces the poudre river is regionally unique in having relatively well developed strath terraces but strath terraces in other major drainages of the front range are also only present upstream from convexities in the longitudinal profile

fire related sedimentation events on alluvial fans yellowstone national park u s a abstract we document initiation and flow processes deposit facies and geomorphic effects of forest fire related sedimentation on small alluvial fans in yellowstone national park brief intense convective storm precipitation on steep basins burned in the 1988 fires produced sedimentation events involving a variety of depositional processes on fans over the course of all documented events flows on fans progressed from higher to lower sediment concentration events were often dominated by either debris flows or relatively sediment poor streamflow processes in some events however flows ranging a over wide spectrum of sediment concentration produced significant fan deposits debris flows were generated by progressive sediment bulking involving pervasive surface runoff and rill erosion on st ep upper basin slopes followed by deep incision as flows progressed down channels debris flow deposits show a marked decline in thickness and coarse gravel content downfan often with extensive distal gravel poor facies we recognized a relatively minor percentage of noncohesive debris flow and hyperconcentrated flow facies with sorting and stratification intermediate between muddy debris flow and streamflow facies these were deposited where dilute flows bulked with coarse sediment by eroding channel alluvium or earlier deposits of the event below incised fan channels streamflows expanded as sheetfloods which prograded lower fans with distally fining deposits basins 3 km2 typically produced streamflow events on fans but sediment texture and availability on slopes and in channels are primary factors determining flow processes on fans of smaller basins burned soil surfaces provided abundant silt and clay for debris flow generation but because soil surface sediment was stripped and or compacted over time the lack of available fines resulted in dominance of streamflow processes in later events

a multiproxy record of postglacial climate variability from a shallowing 12 m deep sub alpine bog in the southeastern san juan mountains of colorado usa pollen assemblages diatom assemblages and sedimentology from cumbres bog in the southeastern san juan mountains of colorado provide a record of climate and environmental change since the end of the last glacial maximum lgm cumbres bog is unusually deep basal sediments extend 12 m below the surface for its altitude 3050 m a s l and we extracted 7 m core of continuous sediment below 5 m of water and peat the resulting record provides strong evidence of a period of warming immediately after the lgm 18 13 cal kyr bp a cool interval coinciding with the younger dryas 12 8 11 5 cal kyr bp a warm stable period from 10 to 6 cal kyr bp and a cooler and highly variable climate interval after 6 cal kyr bp more specifically pollen ratios and fossil diatoms indicate that cold periods generally match with previously identified periods of rapid climate change that occurred at 10 6 8 7 7 9 7 0 6 9 5 4 5 2 3 3 3 0 2 3 2 0 and 1 5 cal kyr bp this record also adds resolution to previous

drained residual shear strength of some claystones from front range colorado drained residual shear strength data on claystone shale bedrock samples from seven sites along the front range in colorado collected from various sources are summarized the claystone bedrock specimens from these sites were from dawson laramie arapahoe and denver formations the testing procedures included reversal direct shear and torsional ring shear tests upper bound lower bound and average residual shear strength envelopes were developed using the data from the seven sites the secant residual friction angle varied from an upper limit of about 30 to a lower limit of about 5 5 for effective normal stress ranging from 30 to 960 kpa selected published correlations relating the drained residual friction angle to the liquid limit plasticity index clay fraction and effective normal stress were also compared to the data set for this particular data set the plasticity index based correlations compared better than the liquid limit based correlations it is recommended that if any published corr

response of bankfull flood magnitudes to holocene climate change uinta mountains northeastern utah long term variations in holocene fl ood magnitude were quantifi ed from the bankfull dimensions of abandoned channels preserved on flsurfaces in the northern uinta mountains of northeastern utah cross sectional areas of abandoned channels were reconstructed and relationships derived from the modern gage records were used to estimate bankfull discharges from bankfull cross section areas the results indicate systematic nonrandom variations of bankfull fl oods in the northern uinta mountains large fl oods as much as 10 15 greater than modern dominated from 8500 to 5000 calendar yr b p and again from 2800 to 1000 cal yr b p small fl oods as much as 15 20 less than modern characterize the periods from 5000 to 2800 cal yr b p and from 1000 cal yr b p to near present the middle and late holocene record of bankfull fl ood magnitude compares well with independent evidence for climatic variation in the area the early holocene record indicates that larger than modern bankfull fl oods coincide with warmer than modern mean annual temperature we hypothesize that an increased range of magnitude for seasonal solar radiation during the early holocene favored the accumulation and rapid melting of deep snowpacks in the high uinta mountains thus producing large fl oods despite warmer mean annual temperatures the episode of smaller than modern bankfull fl oods between 5000 and 2800 cal yr b p coincides with records of increased forest fi re frequency in the northern uintas larger than modern fl oods from 2800 to 1000 cal yr b p coincide with a local decrease in forest fi re frequency and evidence for minor local glacial readvances the decrease in fl magnitudes following 1000 cal yr b p corresponds to numerous local and regional records of warming during the medieval climatic anomaly

numerical modeling of fluvial strath terrace formation in response to oscillating climate many river systems in western north america retain a fluvial strath terrace rec ord of discontinuous downcutting into bedrock through the quaternary their importance lies in their use to interpret climatic events in the headwaters and to determine long term incision rates terrace formation has been ascribed to changes in sediment supply and or water discharge produced by late quaternary climatic fluctuations we use a one dimensional channel evolution model to explore whether temporal variations in sediment and water discharge can generate terrace sequences the model includes sediment transport vertical bedrock erosion limited by alluvial cover and lateral valley wall erosion we set limits on our modeling by using data collected from the terraced wind river basin two types of experiments were performed constant period sinusoidal input histories and variable period inputs scaled by the marine 18 o rec ord our simulations indicate that strath terrace formation requires input variability that produces a changing ratio of vertical to lateral erosion rates straths are cut when the channel floor is protected from erosion by sediment and are abandoned and terraces formed when incision can resume following sediment cover thinning high sediment supply promotes wide valley floors that are abandoned as sediment supply decreases in contrast wide valleys are promoted by low effective water discharge and are abandoned as discharge increases widening of the valley floors that become terraces occurs over many thousands of years the transition from valley widening to downcutting and terrace creation occurs in response to subtle input changes affecting local divergence of sediment transport capacity formation of terraces lags by several thousand years the input changes that cause their formation our results suggest that use of terrace ages to set limits on the timing of a specific event must be done with the knowledge that the system can take thousands of years to respond to a perturbation the incision rate calculated in the field from the lowest terrace in these systems will likely be higher than the rate calculated by using older terraces because the most recent fluvial response in the field is commonly downcutting associated with declining sediment input since the last glacial maximum this apparent increase in incision rates is observed in many river systems and should not necessarily be interpreted as a response to an increase in rock uplift rate

landslide hazard evaluation the landslide hazard curves this paper presents an innovative practical methodology to establish priorities for slope monitoring and the planning of stabilization works in large hilly areas the study is based on the analysis of geological and geomorphological maps identification of catchment areas and the division of catchment areas into primary with main stream and secondary without main stream sub basins attention was focused on secondary sub basins and their characteristics lithology an ad hoc parameter iq related to the average rainfall the size of the basin and the width of the toe section and the average slope inclination ii the technique presented enables the landslide hazard curve unique for a given formation in homogenous areas with similar rainfall conditions and seismicity to be drawn in a chart which features iq and ii all the ascertained and assumed unstable areas represented in the chart are located above the landslide hazard curve the study was carried out scientifically by taking into account engineering aspects geological geomorphological hydrological and geotechnical which influence slope stability groundwater levels important in mapping out landslide prone areas were considered in the study by means of the parameter iq

quaternary evolution of cedar creek alluvial fan montana abstract cedar creek alluvial fan is a textbook example of an alluvial fan because of its fan shape with smooth concentric contours and excellent symmetry similar planimetric shapes have been used to infer uniform fan deposition however cedar creek alluvial fan is composed of four fan deposits of quaternary age qf1 oldest to qf4 youngest indicating that fan deposition was nonuniform in both time and space field studies indicate that deposition of cedar creek alluvial fan is related to glaciofluvial outwash activity during the pleistocene and upper fan entrenchment and lower fan deposition during the holocene qf1 and qf2 deposits are sub horizontally bedded clast supported sandy gravels uniformly imbricated upfan comparison of soil profiles developed in these deposits to radiogenically dated chronosequences within the region indicates that qf1 and qf2 are correlative with bull lake and pinedale age deposits respectively these relationships are substantiated by physical correlation of qf1 and qf2 with bull lake and pinedale moraines respectively in the cedar creek drainage basin the sedimentology and timing of qf1 and qf2 indicate deposition in high energy proglacial braided streams furthermore the present morphology of cedar creek alluvial fan was established largely during aggradation of qf1 and qf2 when sediment supply to the fan was sufficient to activate 60 to greater than 90 of the total fan area during bull lake glaciation the apex of qf1 deposition formed the apex of cedar creek alluvial fan as qf1 covered more than 90 of the present fan area during pinedale glaciation qf2 deposition shifted downfan qf2 is inset into qf1 above the intersection point but below the intersection point it eroded and or buried qf1 as it activated as much as 60 of the fan area qf3 and qf4 comprising 21 of the fan area are inset into qf2 in the lower fan area soil development in qf3 and qf4 deposits indicate episodic deposition and entrenchment beginning in early holocene and continuing to present a post glacial decrease in sediment supply to cedar creek alluvial fan is indicated by sediment storage within the cedar creek drainage basin decreased sediment supply to the fan resulted in upper fan entrenchment of qf2 and deposition of qf3 and qf4 in the lower fan area

beryllium 10 dating of the duration and retreat of the last pinedale glacial sequence accurate terrestrial glacial chronologies are needed for comparison with the marine record to establish the dynamics of global climate change during transitions from glacial to interglacial regimes cosmogenic beryllium 10 measurements in the wind river range indicate that the last glacial maximum marine oxygen isotope stage 2 was achieved there by 21 700 700 beryllium 10 years and lasted 5900 years ages of a sequence of recessional moraines and striated bedrock surfaces show that the initial deglaciation was rapid and that the entire glacial system retreated 33 kilometers to the cirque basin by 12 100 500 beryllium 10 years

an extreme cold air outbreak over the labrador sea roll vortices and air sea interaction abstract observational data from two research aircraft flights are presented the flights were planned to investigate the air sea interaction during an extreme cold air outbreak associated with the passage of a synoptic scale low pressure system over the labrador sea during 8 february 1997 this is the first such aircraft based investigation in this remote region both high level dropsonde and low level flight level data were collected the objectives were twofold to map out the structure of the roll vortices that cause the ubiquitous cloud streets seen in satellite imagery and to estimate the sensible and latent heat fluxes between the ocean and atmosphere during the event the latter was achieved by a lagrangian analysis of the flight level data the flights were part of the labrador sea deep convection experiment investigating deep oceanic convection and were planned to overpass a research vessel in the area the aircraft observed roll vortices had a characteristic wavelength of 4 5 km particular

a postglacial palaeoecological record from the san juan mountains of colorado usa fire climate and vegetation history continuous sediment charcoal and pollen records were developed from a 4 5 m sediment core from little molas lake lml 3370 m elevation san juan county co lml formed by 11 200 cal bp subsequent to glacial retreat turbated clay and gyttja was derived from in lake productivity and outwash sediments from the drainage basin from 1 1 200 cal bp until 10 200 cal bp cessation of glacial input and replacement of tundra with picea forest correlates with the termination of the younger dryas and indicates warming an increase in diploxylon pollen cf p ponderosa probably from lower elevations reflects the influence of the southwestern monsoon c 10 160 cal bp pollen ratios indicate that picea and other conifers persisted near the lake for the remainer of the holocene the driest holocene period occurs c 6200 to 5900 cal bp when lake levels were the lowest as indicated by all the proxy records wetter conditions during the last c 2600 cal bp favoured the expansion of p edulis and p ponderosa lat

middle late holocene river terraces in the erhjen river basin southwestern taiwan implications of river response to climate change and active tectonic uplift abstract we reconstruct the holocene river history of the erhjen river area 140 km 2 by correlating river terraces aided by 28 radiocarbon dates multiple terraces developed in the lower erhjen river since the middle holocene they converge downstream to the coastal plain the rates of channel incision into bedrock calculated from these terraces at yuehshihchieh are 7 8 mm year during ca 5 7 2 5 ka 5 cm year during 1 5 1 3 ka and 1 cm year since 1 ka the last is close to the average incision rate since middle holocene meanwhile only a single but wide middle late holocene paleo floodplain was developed in the upper erhjen river it was completely abandoned only after 0 8 ka likely following an episode of base level fall starting from the coastal plain based on the apparent downstream and upstream convergence of these dated terraces we identify a doming structure or anticline within the basin which results in a tilt rate of 10 6 to 10 7 per year in the lower erhjen river valley the major terraces here had different initial long profiles which implies that a critical graded long profile may not be a prerequisite for formation of a wide erosional terrace surface instead we propose that these terraces were initiated by a series of catastrophic rainfall events probably climatic related which brought a large amount of bedload from hillslopes to prevent the channel from incising when valley widening was facilitated by high discharge runoff we find that not only terrace surface formation but also channel incision can be strongly controlled by climatic driven discharge and bedload conditions as suggested by the contrast of bedrock incision rates we observe at yuehshihchieh apparently the climate and its effects on the landscape cannot be regarded as constant during the holocene even in a humid tropical area like taiwan however such a fluctuation of climate could only be recorded in a setting where rivers have a high tendency to incise so that multiple terraces can be created the lower erhjen river that is characterized by active tectonic tilting is an example of this setting

palynological evidence for late and postglacial environmental change in central colorado abstract a sediment core recovered from lost park 39 17 30 n 105 32 30 w elevation 3079 m provides palynological evidence for postglacial vegetational and environmental change in the central front range of colorado pine spruce woodland was the dominant vegetation type throughout the 12 000 yr long record nonarboreal taxa however showed substantial changes from 11 800 to 9100 14 c yr b p high artemisia levels suggest steppe vegetation indicative of a climate cooler than that at present with an annual precipitation regime dominated by winter moisture the pollen spectra of this interval resemble modern spectra at two sites within colorado and wyoming comparisons of modern climatic data suggest that lost park may have experienced winter temperatures 3 to 3 5 c colder than those at present and monthly winter precipitation levels 3 5 cm higher than those at present during this late glacial time lower artemisia coupled with increases in poaceae pollen suggest a shift to warmer conditions dominated by summer monsoon precipitation around 9100 14 c yr b p increased charcoal occurrences between 6000 and 4000 14 c yr b p may suggest the onset of drier summer conditions that would be expected with a waning summer monsoon circulation at that time since 1800 14 c yr b p a resurgence in artemisia pollen suggests a return to relatively cool and or dry conditions similar to the present climate

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

an isolated cloud band around a typhoon in the western tropical pacific 1 satellite imagery and c band radar on the r v mirai detected an isolated convective cloud band over the western tropical pacific and dropsondes observed the surrounding atmospheric environment the reasonable development mechanism of this unusual cloud band is investigated using observational and numerical simulation data although theoretically the surrounding atmospheric profile supported convective rolls only a single cloud band was developed numerical simulations revealed a single cloud band and roll structure without condensate in the boundary layer a westerly jet just above the cloud band influenced the environment with strong vertical shear supporting convective rolls this was maintained by a typhoon at a distance of 1500 km away a large scale convergence in the meridional wind was also accompanied with this westerly jet this special environment made by a typhoon could develop the unusual single cloud band

the influence of bedrock weathering on the response of drainage basins and associated alluvial fans to holocene climates san bernardino mountains california usa the primary factors that control alluvial fan evolution still remain in question particularly for the holocene holocene centennial and millennial scale climate fluctuations are relatively subtle and more frequent than those of glacial interglacial transitions therefore intrinsic factors such as rock type or basin size are hypothesized to moderate significantly the influence of holocene climate and climate change on alluvial fan processes here we examine variability in styles and rates of alluvial fan aggradation along a single mountain front that is characterized by basins of varying size and rock type carbonate versus granite basin rock type is more closely correlated to variability in the episodic nature and magnitude of alluvial fan aggradation than is basin area bedrock physical and chemical weathering properties control sediment delivery to the piedmont and thus influence alluvial fan aggradation we suggest that the particle size of grus produced by weathering of granitic rocks fosters sedi

dating fluvial terraces with and profiles application to the wind river wyoming abstract fluvial strath terraces provide a record of river incision and the timing of climatic perturbations to the fluvial system dating depositional surfaces like terraces that are older than the range of 14 c however is difficult we employ a cosmogenic radionuclide crn profile technique that addresses a major problem of crn dating on such surfaces nuclide inheritance by measuring 10 be and 26 al profiles we constrain the exposure age and the mean crn inheritance for the deposit the crn profile also yields a self check on the assumptions underlying the method we report our attempts to date terraces along the wind river wy like many sequences of western north american fluvial terraces these are inferred to reflect oscillation between glacial and interglacial conditions in the headwaters previous dating of some of these terraces and the associated terraces and glacial deposits makes this a unique location to compare dating methods dates from five sites along the bull lake glacial correlative terrace wr 3 are 118 125 ka which agrees with dates on bull lake age moraines and independent age estimates on the terrace and is consistent with the model of terrace glacial relationship crn inheritance is significant and highly variable requiring it be considered despite the additional sampling complexity assuming all inheritance in wr 3 deposits arises during exhumation in the headwaters we obtain minimum mean rates of exhumation of 13 130 m my for the source rocks alternatively assuming the crns are inherited during clast transport the time of fluvial transport from source to terrace is 10 ka it increases downstream and is lower for sand than cobbles the crn ages for older terraces wr 7 300 ka and wr 15 510 ka are lower by 50 than previous estimates based on tephrochronology the most plausible explanation is eolian deflation of a once thicker loess cover on the terrace surfaces mean thicknesses of loess of 0 5 1 5 m are required to reconcile these concentrations of crn with the previous estimates of age difficulty in dating the older terraces emphasizes that geologic caution independent estimates of age and multiple sample sites should still be part of dating depositional surfaces with crns even when employing the inheritance correction technique

residual strength of slip zones of large landslides in the three gorges area china abstract slip zones of the large landslides in the three gorges area are commonly composed of fine grained soils with substantial amount of coarse grained particles particularly gravel sized particles in this study residual strength of the soils from slip zones of these landslides were examined in relation to their index properties based on a survey of 170 landslides it was found that laboratory determined residual friction angle using gravel free fraction of the disturbed soils from the slip zones was closely related to clay content liquid limit and plasticity index on the other hand in situ residual friction angle of these soils i e including gravel fraction showed very weak correlations with clay content and atterberg limits but was largely dependent on gravel and fines clays silts contents increasing with gravels and decreasing with fines and displayed strong linear correlation with the ratio of gravel to fines contents these observations indicate that among the index properties clay content and atterberg limits can be used to estimate residual strength of the soils finer than 2 mm but they are not appropriate evaluate the residual strength of the soils containing considerable amount of gravel sized particles for the latter particle size distribution particularly the ratio of gravel to fines contents appears to be a useful index additionally it was found that there was no identifiable correlation between relative abundance of individual major clay minerals and residual friction angles of both gravel free fraction of disturbed and in situ soils suggesting that influence of clay minerals on residual strength of these soils can not be simply evaluated based on their abundance

explicit treatment of inheritance in dating depositional surfaces using in situ 10be and 26al we describe a new strategy for dating depositional landscape surfaces using in situ produced cosmogenic radionuclides crns that removes the complication of nuclide inheritance by clasts prior to depositon two amalgamated samples each consisting of 30 clasts one from the surface and one from a fixed depth in the subsurface constrain this crn inheritance and date the surface the inheritance may be used to estimate minimum exhumation rates and maximum transport times within the geomorphic system we test the technique using sup 10 be and sup 26 al to date the third fr3 of five terraces along the fremont river utah and the third wr3 of 15 along the wind river wyoming whereas effective ages based solely upon the surface samples yield 118 138 ka fr3 and 93 ka wr3 the subsurface samples reveal that inheritance accounts for 22 wr3 to 43 fr3 of the total crn concentration taking this into account yeilds terrace ages of nearly 61 81 ka for fr3 and nearly 67 76 ka for wr3 we explore the dependence of age estimates on the accumulation history of the terrace silt caps 22 refs 3 figs 1 tab

empirical correlations drained shear strength for slope stability analyses empirical correlations provide estimates of parameter values for preliminary design verification of laboratory shear test data and confirmation of back analysis of a failed slope the empirical correlations presented herein use liquid limit clay size fraction and effective normal stress to capture the variability and stress dependent nature of drained residual and fully softened strength envelopes this paper describesthetestingandanalysisusedtoincreasethenumberofdatapointsintheexistingcorrelations expandtheresidualstrengthcorrelation to include an effective normal stress of 50 kpa and develop correlations between values of liquid limit and clay size fraction measured using sampleprocessedthroughano 40sieve astmprocedure andvalues derivedusingball milled disaggregated sample inaddition equations are presented to express the empirical correlations used to develop a spreadsheet that estimates the residual and fully softened friction angles based on entered values of liquid limit and clay size fraction doi 10 1061 asce gt 1943 5606 0000824 2013 american society of civil engineers ce database subject headings shear strength friction clays shale slope stability drainage author keywords shear strength residual friction angle fully softened friction angle empirical correlation clay shale

cosmic ray production rates of 10be and 26al in quartz from glacially polished rocks we have studied the concentrations of 10be and 26al in quartz crystals extracted from glacially polished granitic surfaces from the sierra nevada range these surfaces were identified with the glacial advance during the tioga period 11 000 years ago our measurements yield the most accurate estimates to date for the absolute production rates of these nuclides in sio2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43 8 44 6 n and altitudes 2 1 3 6 km the estimates are relatively free from uncertainties in snow cover since we studied a suite of rock surfaces inclined 0 75 with respect to the horizontal the principal uncertainty arises due to the lack of a precise date for the glacial retreat event about 10 the 26al 10be ratio at production 6 0 is determined more accurately since the exposure age of the samples is 2 orders of magnitude smaller than the mean lives of the two nuclides production rates of 10be and 26al in quartz at other latitudes and altitudes in the troposphere can be determined from the present measurements by scaling using the known altitude and latitude dependence of cosmic ray fluxes of nucleons and negative muons knowledge of the production rates of these nuclides is a prerequisite for their application in erosion and geomorphological studies

platy layer silicate minerals for controlling residual strength in landslide soils of different origins and geology we use a ring shear apparatus to examine the relationship between the residual strength and mineralogical properties of landslide soils and find a significant relation between the residual strength parameter r and the total content of layer silicate minerals prone to preferred orientation within the bulk soil in this context the total content of smectite vermiculite chlorite and mica in the sub 425 m soil fraction is a suitable mineralogical parameter for estimating the magnitude of r plotting r as a function of total mineral content forms a chair shaped curve based on which we classify landslide soils into three groups in the first group of soils sliding appears to be controlled by minerals such as quartz feldspar calcite dolomite and layer silicate minerals other than smectite vermiculite chlorite and mica and their r is almost constant at 32 in the second group of soils the controlling mineralogical factor for sliding quickly shifts from nonpreferred orientation minerals to preferred orientation minerals and r decreases from 30 to 10 in the third group of soils sliding is well controlled by preferred orientation layer silicate minerals and r gradually decreases from 10 to 5 the results show that the relationship can be used for predicting r of a wide range of landslide soils that differ in geology soil type mineralogical properties and shear strength

uplift driven valley incision and climate controlled river terrace development in the thames valley uk abstract the sequence of terraces of the river thames in southeast england has previously been shown to span the period from the earliest pleistocene to the present this terrace sequence contains biostratigraphical and sedimentary evidence that testifies to the high amplitude climatic changes of the quaternary large scale fluvial incision resulting in basin wide terrace formation appears to have been concentrated at the warming limbs of the major climatic glacial interglacial cycles when sediment supply was greatly reduced this incision and subsequent valley floor widening created the accommodation space for the later aggradation of the terrace sediments during the following warm cold transitions and during the cold stages when high sediment supply conditions prevailed although the timing of terrace aggradation may be controlled by climate change the progressive valley incision recorded by terrace staircases cannot easily be explained in terms of quaternary climatic change alone and recently developed models suggest that long term incision by the thames has been driven by uplift this paper presents an overview of the available terrace data and tabulates incision amounts and rates between key stratigraphic horizons superimposed upon these broad changes revealed by the complex internal sedimentary architecture of many terrace sediments are the geomorphological system responses to both higher frequency climate driven changes and more localized intrinsic fluvial system adjustments

fire and alluvial chronology in yellowstone national park climatic and intrinsic controls on holocene geomorphic processes we employed a systemwide approach a large and robust set of radiocarbon ages and modern process analogs to interpret the holocene history of forest fire related sedimentation and overall alluvial activity in northeastern yellowstone national park debris flow and flood events following the 1988 fires provided facies models for interpreting the stratigraphic record of fire related sedimentation within valley side alluvial fans of soda butte creek fire related deposits make up approximately 30 of the late holocene fan alluvium fifty 14 c ages on fire related events cluster within the intervals of 3300 2900 2600 2400 2200 1800 and 1400 800 yr b p and suggest earlier episodes of large fires and fan aggradation around 7500 5500 and 4600 4000 yr b p a major pulse of fire related debris flow activity between 950 and 800 yr b p coincided with the height of the widely recognized medieval warm period ca a d 1050 1200 instrumental climate records over the last 100 yr in yellowstone imply that the intensity and interannual variability of summer precipitation are greater during warmer periods enhancing the potential for severe short term drought major forest fires and storm generated fan deposition along lower soda butte creek fill cut terrace treads were created by lateral migration of channels and accumulation of overbank sediments ca 8000 yr b p terrace level t1a 7000 5600 t1b 3100 2600 t2 2000 1300 t3 and post 800 yr b p t4 these periods coincide with overbank sedimentation on slough creek and the lamar river but alternate with intervals of fire related fan deposition implying a strong climatic control local paleoclimatic data suggest cooler effectively wetter conditions during terrace tread formation in warmer drier intervals reduced average runoff in axial streams results in meander belt narrowing concurrent channel incision may be caused by infrequent large floods greater resistance to downcutting however allowed fewer terraces to be formed along slough creek and the lamar river alluvial systems in northeastern yellowstone show a clear response to millennial scale climatic cycles wherein alluvial fans aggrade and prograde over flood plains in drier periods axial streams widen their flood plains and trim back the fans during wetter periods small scale climatic fluctuations of the holocene thus had substantial impact on postglacial landscapes in northeastern yellowstone

an observational case for the prevalence of roll vortices in the hurricane boundary layer abstract doppler velocity data from weather surveillance radar 1988 doppler wsr 88d radars during four hurricane landfalls are analyzed to investigate the presence of organized vortices in the hurricane boundary layer hbl the wavelength depth magnitude and track of velocity anomalies were compiled through analysis of doppler velocity data the analysis reveals alternating bands of enhanced and reduced azimuthal winds closely aligned with the mean wind direction resulting statistics provide compelling evidence for the presence of organized secondary circulations or boundary layer rolls across significant areas during four hurricane landfalls the results confirm previous observations of the presence of rolls in the hbl a potential limitation of the study presented here is the resolution of the wsr 88d data in particular analysis of higher resolution data e g from the doppler on wheels is needed to confirm that data aliasing has not unduly impacted the statistics reported here momentum flux

sedimentology and clast fabric of subaerial debris flow facies in a glacially influenced alluvial fan abstract a large alluvial fan 2 km2 constructed between 11 000 and 7000 years b p at the mouth of cinquefoil creek in interior british columbia canada is identified as glacially influenced debris flow dominated the fan was rapidly constructed during and immediately after deglaciation when large volumes of glacial debris were resedimented downslope fans of this type are widespread in the glaciated portion of the north american cordillera diamict facies deposited as debris flows account for 48 of the fan volume sheetflodd gravels 37 and other facies 15 diamicts show three facies types crudely bedded facies containing rafts of soft sediment that are attributed to downslope collapse and mixing of heterogeneous glacial deposits these occur within the core of the fan massive and weakly graded inverse to normal diamict facies derived from the downslope flow of weathered volcanic bedrock occur within a well defined bed that can be traced across the entire fan the occurrence of weakly graded facies as lateral equivalents to massive facies within the same bed implies the partial development of turbulent high velocity streams within a viscous debris flow moving over a slope of 6 clast fabrics in these facies show weakly clustered a axes dipping up and downslope comparable to other debris flows and lahars the cinquefoil fan its internal structure and facies provides a good modern analogue for ancient diamictite sequences deposited in areas of active uplift rifting and glaciation

cosmogenic chlorine 36 chronology for glacial deposits at bloody canyon eastern sierra nevada deposits from mountain glaciers provide an important record of quaternary climatic fluctuations but have proved difficult to date directly a chronology has been obtained for glacial deposits at bloody canyon california by measurement ofthe accumulation of chlorine 36 produced by cosmic rays in boulders exposed on moraine crests the accumulation ofchlorine 36 indicates that episodes of glaciation occurred at about 21 24 65 115 145 and 200 ka thousand years ago although the timing of the glaciations correlates well with peaks of global ice volume inferred from the marine oxygen isotope record the relative magnitudes differ markedly the lengths of the moraines dating from 115 ka and 65 ka show that the early glacial episodes were more extensive than those during the later wisconsin and indicate that the transition from interglacial to full glacial conditions was rapid

mesoscale shallow convection in the atmosphere this paper is a review of the observational experimental theoretical and numerical studies of mesoscale shallow convection msc in the atmosphere typically msc is 1 to 2 km deep has a horizontal length scale of a few to a few tens of kilometers and takes distinctive planforms linear and hexagonal the former is called a cloud street roll or band while the latter is called mesoscale cellular convection mcc comprising three dimensional cells msc is characterized by its shape horizontal extent convective depth and aspect ratio the latter is the ratio of the horizontal extent to that in the vertical for cells the horizontal extent is their diameter whereas for rolls it is their spacing rolls usually align along or at angles of up to 10 from the mean horizontal wind of the convective layer with lengths from 20 to 200 km widths from 2 to 10 km and convective depths from 2 to 3 km the typical value of aspect ratio ranges from 2 to 20 rolls may occur over both water surface and land surfaces mesoscale convective cells may be divided into two types open and closed open cell circulation has downward motion and clear sky in the cell center surrounded by cloud associated with upward motion closed cells have the opposite circulation both types of cell have diameters ranging from 10 to 40 km and aspect ratios of 5 to 50 and both occur in a convective layer with a depth of about 1 to 3 km both the magnitude and direction of horizontal wind in the convective layer change little with height msc results from a complex and incompletely understood mix of processes these processes are outlined and their interplay is examined through a review of theoretical and laboratory analyses and numerical modeling of msc