erosion by pyroclastic flows on lascar volcano chile pyroclastic flows generated in the 19 20 april 1993 eruption of lascar volcano chile produced spectacular erosion features scree and talus were stripped from the channels and steep slopes on the flanks of the volcano exposed bedrock and boulders suffered severe abrasion producing smoothed surfaces on coarse breccias and striations and percussion marks on bedrock and large boulders erosional furrows developed with wavelengths of 0 5 2 m and depths of 0 1 0 3 m furrows commonly nucleated downstream of large boulders or blocks which are striated on the upstream side and thereby produced crag and tail structures erosive features were produced where flows accelerated through topographic restrictions or where they moved over steep slopes the pyroclastic flows are inferred to have segregated during movement into lithic rich and pumice rich parts lithic rich deposits occur on slopes up to 14 whereas pumice rich deposits occur only on slopes less than 4 and mainly at the margins and distal parts of the 1993 fan the lithic rich deposits contain large up to 1 m lithic clasts eroded from the substrate and transported from the vent whereas pumice rich deposits contain only small typically 2 cm lithic clasts these observations suggest that lithic clasts segregated to the base of the flows and were responsible for much of the erosive phenomena the erosive features distribution of lithic clasts and deposit morphology indicate that the 1993 flows were highly concentrated avalanches dominated by particle interactions in some places the flows slid over the bedrock causing abrasion and long striations which imply that large blocks were locked in fixed positions for periods of about 1 s however shorter striae at different angles impact marks segregation of the deposits into pumice and lithic rich parts and mixing of bedrock derived lithic clasts throughout the deposits indicate that clasts often had some freedom of movement and that jostling of particles allowed internal mixing and density segregation to occur within the flows

the 1930s dust bowl geoarchaeological lessons from a 20th century environmental crisis the dust bowl of the 1930s was an environmental crisis of epic proportions characterized by unprecedented soil erosion population redistribution and profound transformation of the landscape in th

a 250 000 year record of lunette dune accumulation on the southern high plains usa and implications for past climates abstract a concentration of lake playa basins occurs on the southern high plains shp of northwest texas and eastern new mexico associated with these lake playas are lee side lunettes positioned on their southeast margins ranging in height from 1 5 to 10 m an osl dating program was applied to 30 samples from lunettes associated with large lakes and small playa basins samples were extracted from trenched dune sections or from deep cores earlier shp lunette investigations show depositional ages primarily in the late wisconsin and holocene this research extends the timing of lunette accretion to the middle pleistocene the earliest recorded deposition for these features the expanded chronology permitted investigation into dune morphology on nested lunettes built on contracting lake margins outer lunettes formed prior to inner dunes but simultaneous deposition occurred on downwind ridges as younger lee side dunes were constructed large lake lunettes were inactive during discreet shp pluvial episodes from early wisconsin to lgm conversely these lunettes accreted when climatic conditions promoted basin desiccation and aeolian deflation this suggests their mode of formation contrasts with lunette models recognized for other regions from post lgm to earliest holocene active lunette accretion occurred from 16 to 11 ka followed by a significant period of lunette construction during the mid holocene late holocene lunette deposition was interrupted by intervals of landscape stability lunette deposition between 1300s and 1700s corresponds with drought intervals recognized in tree ring records from adjacent regions recent lunette activity on the plateau is contemporary with the 1930 s dust bowl further insight into shp response to changing climatic conditions was given by comparing lunette depositional events with previous investigations on sedimentation intervals for draws lake playa basins and sand sheets

the architecture eruptive history and evolution of the table rock complex oregon from a surtseyan to an energetic maar eruption abstract the table rock complex trc pliocene pleistocene first documented and described by heiken heiken g h 1971 tuff rings examples from the fort rock christmas lake valley basin south central oregon j geophy res 76 5615 5626 is a large and well exposed mafic phreatomagmatic complex in the fort rock christmas lake valley basin south central oregon it spans an area of approximately 40 km2 and consists of a large tuff cone in the south trc1 and a large tuff ring in the northeast trc2 at least seven additional smaller explosion craters were formed along the flanks of the complex in the time between the two main eruptions the first period of activity trc1 initiated with a surtseyan style eruption through a 60 70 m deep lake the trc1 deposits are dominated by multiple 1 2 m thick fining upward sequences of massive to diffusely stratified lapilli tuff with intermittent zones of reverse grading followed by a finely laminated cap of fine grained sediment the massive deposits are interpreted as the result of eruption fed subaqueous turbidity current deposits whereas the finely laminated cap likely resulted from fallout of suspended fine grained material through a water column other common features are erosive channel scour and fill deposits massive tuff breccias and abundant soft sediment deformation due to rapid sediment loading subaerial trc1 deposits are exposed only proximal to the edifice and consist of cross stratified base surge deposits the eruption built a large tuff cone above the lake surface ending with an effusive stage which produced a lava lake in the crater 365 m above the lake floor a significant repose period occurred between the trc1 and trc2 eruptions evidenced by up to 50 cm of diatomitic lake sediments at the contact between the two tuff sequences the trc2 eruption was the last and most energetic in the complex general edifice morphology and a high percentage of accidental material suggest eruption through saturated trc1 deposits and or playa lake sediments trc2 deposits are dominated by three dimensional dune features with wavelengths 200 500 m perpendicular to the flow and 20 200 m parallel to the direction of flow depending on distance from source large u shaped channels 10 32 m deep run up features over obstacles tens of meters high and a large 13 m chute and pool feature are also identified the trc2 deposits are interpreted as the products of multiple erosive highly inflated pyroclastic surges resulting from collapse of an unusually high eruption column relative to previously documented mafic phreatomagmatic eruptions

inferring pyroclastic density current flow conditions using syn depositional sedimentary structures the processes occurring in the basal region of concentrated pyroclastic density currents pdcs influence the mobility runout distance and damage potential of a current but directly observing these processes is extremely difficult instead we must investigate the deposits to glean information regarding the conditions of sediment transport and deposition the pdc deposits of the may 18 1980 eruption of mount st helens wa usa contain sedimentary structures consisting of bed material reworked into undulose structures and recumbent flame structures the structures vary over two orders of magnitude in size with lengths ranging from 8 cm to 18 m and heights ranging from 4 cm to 1 8 m despite the large range in sizes the structures remain self similar in form suggesting a common mechanism for formation the structures are interpreted as the record of granular shear instabilities similar to kelvin helmholtz instabilities formed at the interface between a shearing high concentration flow and the substrate in the moments just prior to deposition the morphology of the structures suggests that the basal region of pdcs must be both highly concentrated and also highly mobile in the moments before final deposition likely a result of elevated pore fluid pressures we use a modified instability growth criterion to estimate pdc flow velocities at the time of formation for the mount st helens pdcs the velocity estimates range from 0 2 to 7 5 m s 1 with larger structures requiring higher flow velocities combining the velocity estimates with the dimensions of the structures suggests deposition rates of 4 to 32 cm s 1 such high deposition rates indicate that the deposits likely accumulated in a stepwise manner rather than either progressively or en masse the structures suggest that sections of the deposit accumulated during punctuated periods of high deposition lasting at most a few seconds followed by periods of bypassing i e non deposition or erosion lasting minutes to tens of minutes our findings motivate continued experimental and numerical work to understand how the formation of recumbent flame and similar structures affects subsequent flow behavior in terms of runout distance and hazard potential

erosional furrows formed during the lateral blast at mount st helens may 18 1980 nearly horizontal quasi periodic erosional features of 7 m average transverse wavelength and of order 100 m length occur in scattered locations from 3 5 to 9 km from the crater at mount st helens under deposits of the lateral blast of may 18 1980 we attribute the erosional features to scouring by longitudinal vortices resulting from flow instabilities induced by complex topography namely by streamline curvature in regions of reattachment downstream of sheltered regions and by the cross flow component of flow subparallel to ridge crests the diameter of the vortices and their transverse spacing inferred from the distance between furrows are taken to be of the order of the boundary layer thickness the inferred boundary layer thickness 14 m at 9 km from the source of the blast is consistent with the running length from the mountain to the furrow locations by using knowledge of ablation patterns on bodies and lofting of dust in high speed flow we are able to infer some features of the flow field within the blast within the furrows the erosion rate was of the order of 9 kg m 2 s 1 about 4 times greater than that expected from laboratory data obtained in flow free of longitudinal vortices the orientation of furrows induced by the cross flow instability can be used to measure the upwash angle and estimate the flow mach number at the central ridge of spirit lake the mach number is inferred to have been about 2 5 and the flow velocity approximately 235 m s the similarities and differences between the furrows reported here and channels observed at other volcanoes are discussed

majindeite mg2mo3o8 a new mineral from the allende meteorite and a witness to post crystallization oxidation of a ca al rich refractory inclusion majindeite ima 2012 079 mg 2mo 3o 8 is a new mineral occurring as submicrometer sized crystals with ni fe and ru os ir alloys apatite and nb oxide the observed assemblages are partially or wholly enclosed by mgal 2o 4 spinel in a type b1 ca al rich inclusion acm 2 from the allende cv3 carbonaceous chondrite the type majindeite has an empirical formula of mg 1 57 fe 0 43 mo 3 00 o 8 and a nolanite type p6 3mc structure with a 5 778 a c 9 904 a v 286 35 a3 and z 2 leading to a calculated density of 5 54 g cm 3 majindeite likely formed during the subsolidus oxidation of mo rich precursor phase s included in fe ni rich alloys in a system that was open to o mg and ca which were derived externally and introduced via cracks subgrain boundaries and or surfaces exposed at the exterior of the spinel if magnetite existed in the phase assemblage it was lost due to fe volatilization prior to the formation of majindeite the immediate precursor to majindeite was likely kamiokite majindeite formed during an oxidation event contemporaneous with or postdating the formation of grossular rich veins in melilite kamiokite the fe rich analog of majindeite also occurs in acm 2 but only within phase assemblages that contain magnetite and which are entirely enclosed in melilite alteration products here grossular rich veins are not observed and the coexisting awaruites are more fe rich than those observed with majindeite as with majindeite the precursors for kamiokite grains were also likely to have been mo rich alloys but the mo oxide remained magnetite saturated throughout the alteration process and therefore remained fe rich

evidence of erosional self channelization of pyroclastic density currents revealed by ground penetrating radar imaging at mount st helens washington usa the causes and effects of erosion are among the least understood aspects of pyroclastic density current pdc dynamics evidence is especially limited for erosional self channelization a process whereby pdcs erode a channel that confines the body of the eroding flow or subsequent flows we use ground penetrating radar imaging to trace a large pdc scour and fill from outcrop to its point of inception and discover a second larger pdc scour and fill the scours are among the largest pdc erosional features on record at 200 m wide and at least 500 m long estimated eroded volumes are on the order of 106 m3 the scours are morphologically similar to incipient channels carved by turbidity currents erosion may be promoted by a moderate slope 5 15 substrate pore pressure retention and pulses of increased flow energy these findings are the first direct evidence of erosional self channelization by pdcs a phenomenon that may increase flow velocity and runout distance through confinement and substrate erosion

non linear connections between dune activity and climate in the high plains kansas and oklahoma usa discrete dune fields are found throughout much of the great plains of north america and the timing of past dune activity is often used as a proxy for paleoclimate because of the intuitive link between dune activity and a more arid climate this research suggests that feedbacks in the soil geomorphic system create a relationship between dune activity and climate that varies both spatially and temporally older eolian landforms are more resistant to activation because of the long term accumulation of finer soil particles in a bt horizon which retain moisture and anchor the deposit even during more arid times conversely younger deposits lack these fines and are more easily reactivated this spatially variable relationship is supported by soil stratigraphy particle size analysis and optical age control additionally the water retention of the bt horizons is quantifiably greater than that of the soils found in the younger dunes of the area this complication in the relationship between eolian activity and climate is important because it suggests that caution is needed when using past dune activity as the lone proxy for paleoclimate

incorporation and redistribution of locally derived lithic fragments within a pyroclastic flow the lower miocene peach springs tuff exposed in the newberry mountains california was deposited within a paleovalley trending s65 w exposures within the paleovalley contain lithic breccia intercalated with ash rich ignimbrite the clast assemblage of the lithic breccias matches the rock types of the paleovalley walls and therefore the clasts were not derived from a distant eruptive vent flow direction breccia bed thickness grain size data and sedimentary textures indicate that the lithic breccias were deposited from density currents within the pyroclastic flow that moved down tributaries and into the main paleovalley to be intermingled with the ash rich pyroclastic flow a model is proposed whereby a turbulent boundary layer at the base of the pyroclastic flow is induced by surface roughness of the substrate and incorporates loose material from the substrate to produce a high density ground layer that decouples from the lower density ash rich pyroclastic flow after decoupling has occurred the high density lithic rich ground layer moves independently from the ash rich pyroclastic flow the lithic breccia horizons have many characteristics of proximal lag breccias and caution must be used when inferring distance from vent in ancient ignimbrites based on the occurrence of coarse breccias

gas retention in fine grained pyroclastic flow materials at high temperatures the ability of a dense pyroclastic flow to maintain high gas pore pressure and hence low friction during runout is determined by 1 the strengths and longevities of gas sources and 2 the ability of the material to retain residual gas once those sources become ineffective the latter is termed the gas retention capacity gas retention capacity in a defluidizing granular material is governed by three timescales one for the evacuation of bubbles t be brief and not considered in this paper one for hindered settling from the expanded state t sett and one for diffusive release of residual pore pressure from the non expanded state t diff the relative magnitides of t sett and t diff depend on bed thickness t sett dominating in thin systems and t diff in thick ones three pyroclastic flow materials two ignimbrites and a block and ash flow sample were studied experimentally to investigate expansion behaviour under gas flow and to determine gas retention times effects of particle size were evaluated by using two size cuts 4 mm and 250 m from each sample careful drying of the materials was necessary to avoid effects of humidity related cohesion two sets of experiments were carried out 1 expansion in the non bubbling regime at 50 200 c 2 bed collapse tests from the initially bubbling state at 50 550 c provided that gas channelling was avoided by gentle stirring all the samples exhibited a regime of uniform expansion prior to the onset of bubbling fine particle size in particular high fines content low particle density and high temperature all favoured smoother fluidization by increasing the maximum expansion possible in the non bubbling state an empirical equation describing the uniform expansion of the materials was determined high temperature also favoured greater gas partitioning into the dense phase of the bubbling bed as well in finer grained samples as higher voidage in the settled bed large values of t sett and t diff were favoured by fine particle size temperature had less influence suggesting that experimental results at low temperatures 50 200 c can be extrapolated to higher temperatures gas retention times provide insight into the ability of pyroclastic flows in expanded t sett or non expanded t diff flow states to retain gas once air ingestion or gas production have become ineffective finer grained pyroclastic flows are expected to retain gas longer and hence to have higher apparent mobilities than coarser grained ones of comparable volume as has been observed on montserrat

characteristics and transport mechanism of the nyixoi chongco rock avalanche on the tibetan plateau china abstract for studying rock avalanches complex surficial and internal characteristics have been regarded as important indicators for understanding avalanche transport mechanism in the present study deposits of a massive holocene rock avalanche termed the nyixoi chongco rock avalanche located on the lhasa terrane of tibetan plateau in china are investigated based on a combination of remote sensing data and in situ observations it is revealed that abundant surface landforms including toreva blocks longitudinal and transverse ridges en echelon ridges and hummocks are commonly developed corresponding to these surface morphologies a series of internal sedimentary structures including jigsaw structures inner shear zones aligned clasts diapiric structures convoluted laminations and basal decollements are also well developed through an analysis of these surficial and internal characteristics we propose that a rapid motion similar to a laminar flow most likely occurred after the avalanche mass detaching from the source area in this process the detached avalanche mass was mainly emplaced by a frictional simple shear process characterized by a bulldozing effect that occurred between the sliding mass and the substrate from the proximal to the distal sections of the avalanche the transport of the rock mass can be classified into four major processes an extension dominated sliding process in the transition zone a compression dominated sliding process in subzones iii 1 and iii 2 of the accumulation zone iii a sliding process co dominated by compression and lateral spreading in subzone iii 3 and a rapid radial spreading process in subzone iii 4 the results of our study provided an improved understanding of the transport mechanisms of this rock avalanche

numerical modeling of self channeling granular flows and of their levee channel deposits when not laterally confined in valleys pyroclastic flows create their own channel along the slope by selecting a given flowing width furthermore the lobe shaped deposits display a very specific morphology with high parallel lateral levees a numerical model based on saint venant equations and the empirical variable friction coefficient proposed by pouliquen and forterre 2002 is used to simulate unconfined granular flow over an inclined plane with a constant supply numerical simulations successfully reproduce the self channeling of the granular lobe and the levee channel morphology in the deposits without having to take into account mixture concepts or polydispersity numerical simulations suggest that the quasi static shoulders bordering the flow are created behind the front of the granular material by the rotation of the velocity field due to the balance between gravity the two dimensional pressure gradient and friction for a simplified hydrostatic model competition between the decreasing friction coefficient and increasing surface gradient as the thickness decreases seems to play a key role in the dynamics of unconfined flows the description of the other disregarded components of the stress tensor would be expected to change the balance of forces the front s shape appears to be constant during propagation the width of the flowing channel and the velocity of the material within it are almost steady and uniform numerical results suggest that measurement of the width and thickness of the central channel morphology in deposits in the field provides an estimate of the velocity and thickness during emplacement citation mangeney a f bouchut n thomas j p vilotte and m o bristeau 2007 numerical modeling of self channeling granular flows and of their levee channel deposits

deconstructing a polygenetic landscape using lidar and multi resolution analysis abstract it is difficult to deconstruct a complex polygenetic landscape into distinct process form regimes using digital elevation models dems and fundamental land surface parameters this study describes a multi resolution analysis approach for extracting geomorphological information from a lidar derived dem over a stabilized aeolian landscape in south texas that exhibits distinct process form regimes associated with different stages in landscape evolution multi resolution analysis was used to generate average altitudes using a gaussian filter with a maximum radius of 1 km at 20 m intervals resulting in 50 generated dems this multi resolution dataset was analyzed using principal components analysis pca to identify the dominant variance structure in the dataset the first 4 principal components pc account for 99 9 of the variation and classification of the variance structure reveals distinct multi scale topographic variation associated with different process form regimes and evolutionary stages our results suggest that this approach can be used to generate quantitatively rigorous morphometric maps to guide field based sedimentological and geophysical investigations which tend to use purposive sampling techniques resulting in bias and error

lidar derived morphology of the 1993 lascar pyroclastic flow deposits and implication for flow dynamics and rheology abstract pumice flows are potentially destructive volcanic events that derive from eruption column collapse and whose dynamics are poorly understood the challenges in studying these flows include the lack of constraints on the dynamics kinematics and initial conditions that control their emplacement we present a morphological study of the distal deposits lobes of the pumice flows resulting from the 1993 eruption at lascar chile the surface geometry of the lobes was measured in detail using a lidar device which allowed for detailed characterisation of their morphology consisting of central channel and lateral levees and terminal frontal snout in particular we find that the ratio of channel levee height as a function of the ratio of the distance between levees total width of the lobe has a characteristic curve for these pumice flow lobes our analysis of several of the lascar pumice lobe deposits south east sector identified several dimensionless groups of the available parameters which when compared against published results from both experimental and numerical investigations allowed us to constrain crucial kinematic and dynamic information on the terminal phase of the pumice flows notably we estimate the velocity of the terminal phase of pumice flows to be 5 10 m s froude numbers of 1 5 2 are comparable with values found for experimental granular flows height width aspect ratios for the levee channel section of the pumice lobes are similar to those for experimental flows although these same aspect ratios for the snout are much larger for the natural deposits than their small scale analogues finally we discuss the possible emplacement dynamics of the terminal lascar 1993 pumice flows a pseudo reynolds number based on the velocity estimation is found to be up to 100 times larger for the pumice flows than experimental scale flows this suggests that the flow retarding frictional forces for large scale flows are relatively unimportant compared to flows at smaller scales mechanical effects such as fluidisation mobilisation of material lying on the slopes over which they propagate and lubrication due to polydispersivity could provide an explanation for their ability to propagate on shallow slopes 6 11

hibonite fe fe mg al12o19 a new alteration mineral from the allende meteorite hibonite fe fe mg al 12 o 19 is the fe 2 dominant analog of hibonite caal 12 o 19 discovered in a highly altered ca al rich refractory inclusion from the allende meteorite it occurs as scattered micrometer sized single crystals within an aggregate of hercynite fe mg al 2 o 4 adjacent to nepheline ilmenite ferroan spinel perovskite and hibonite the mean chemical composition determined by electron microprobe analysis of hibonite fe is al 2 o 3 90 05 wt feo 3 60 sio 2 2 09 mgo 1 61 na 2 o 0 55 cao 0 28 tio 2 0 04 v 2 o 3 0 02 sum 98 25 corresponding to an empirical formula of fe 2 0 34 mg 0 27 na 0 12 al 0 11 ca 0 03 0 87 al 11 77 si 0 23 12 00 o 19 hibonite fe is hexagonal p6 3 mmc a 5 613 a c 22 285 a v 608 0 a 3 and z 2 its electron backscatter diffraction pattern is a good match to that of the hibonite structure hibonite fe is apparently a secondary alteration product formed by iron alkali halogen metasomatism whereas hibonite is a primary refractory phase

dynamics of pyroclastic density currents conditions that promote substrate erosion and self channelization mount st helens washington usa abstract the may 18th 1980 eruption of mount st helens msh produced multiple pyroclastic density currents pdcs burying the area north of the volcano under 10s of meters of deposits detailed measurements of recently exposed strata from these pdcs provide substantial insight into the dynamics of concentrated currents including inferences on particle particle interactions current mobility due to sedimentation fluidization and internal pore pressure particle support mechanisms the influence of surface roughness and the conditions that promote substrate erosion and self channelization four primary flow units are identified along the extensive drainage system north of the volcano each flow unit has intricate vertical and lateral facies changes and complex cross cutting relationships away from source each flow unit is an accumulation from an unsteady but locally sustained pdc or an amalgamation of several pdc pulses the pdcs associated with units i and ii likely occurred during the pre climactic waxing phase of the eruption these currents flowed around and filled in the hummocky topography leaving the massive to diffusely stratified deposits of units i and ii the deposits of both units i and ii are generally more massive in low lying areas and more stratified in areas of high surface roughness suggesting that surface roughness enhanced basal shear stress within the flow boundary units iii and iv are associated with the climactic phase of the eruption which produced the most voluminous and wide spread pdcs both flow units are characteristically massive and enriched in vent derived lithic blocks these currents flowed over and around the debris avalanche deposits as evidenced by the erosion of blocks from the hummocks unit iii is massive poorly sorted and shows little to no evidence of elutriation or segregation of lithics and pumice suggesting a highly concentrated current where size density segregation was suppressed unit iv shows similar depositional features but typically has a basal lithic rich region is variably fines depleted and contains pumice lobes suggesting density segregation in a less concentrated current relative to unit iii deep erosive channels cut by the unit iii current and thick lithic levee deposits within unit iv occur in an area where debris avalanche relief is limited suggesting self channelization developed as a function of internal flow dynamics an increase in the proportion and size of lithic blocks is found 1 downstream of debris avalanche hummocks suggesting the pdcs were energetic enough to locally entrain accidental lithics from the hummocks and transport them tens of meters downstream and 2 within large channels cut by later pdcs into earlier pdc deposits suggesting self channelization of the flows increased the carrying capacity of the subsequent channelized currents finally the combination of thick massive deposits with a high percentage of fine ash within unit iii and in the medial distal depositional regions of units ii iv suggests that the pdcs developed and maintained a high internal pore pressure during transport and deposition the most important results include our ability to understand the role of internal pore pressure on current mobility the influence of self channelization on carrying capacity of the currents and the influence of surface roughness on substrate erosion these observations have critical consequences for understanding the flow dynamics and hazard potential of pdcs

dynamic pore pressure variations induce substrate erosion by pyroclastic flows field evidence shows that pyroclastic flows can entrain blocks from underlying substrates formed by earlier geological events yet counterintuitively they are less likely to erode unconsolidated layers of fine particles here we report laboratory experiments that reproduce these seemingly contradictory observations and also offer a means to infer pyroclastic flow velocity experiments demonstrate that the sliding head of a granular flow generates a dynamic upward pore pressure gradient at the flow substrate interface associated upward air flux is enough to fluidize a substrate of fines so that particles are not entrained individually but the substrate instead is subject to small shear instabilities in contrast coarse particles forming a non fluidized substrate are lifted at a critical upward force due to the pore pressure gradient according to their individual masses which provides a basis for a model to calculate the flow velocity application to the 18 may 1980 pyroclastic flow deposits at mount st helens washington state usa gives velocities of 9 13 m s 1 at 6 7 km from the vent on gentle slopes 4 6 in agreement with field observations at this volcano and at others

spatial and temporal patterns of late quaternary eolian deposition eastern colorado u s a abstract eolian sediment covers about 60 of colorado east of the rocky mountains about 30 of the sediment is sand and 70 is loess initially flood plains were the principal sources of eolian sediment but during the holocene dunes formed from older eolian sand and alluvium on uplands since latest pleistocene time dominant dune forming winds have been northwesterly in the northern part of the region and southwesterly in the southern part at present sand sheets and dunes mainly parabolic types are stable and covered with vegetation in dunes sand is commonly 20 30 m thick but elsewhere averages

late quaternary environmental change inferred from phytoliths and other soil related proxies case studies from the central and southern great plains usa abstract this study investigates stable carbon isotopes 13c opal phytolith assemblages burnt phytoliths microscopic charcoal and sporormiella spores from modern soils and paleosols in kansas and oklahoma grass and dicot phytoliths in combination with 13c are used as proxies for reconstructing the structure of grasslands and woodlands burnt grass phytoliths and microscopic charcoal are evaluated as proxies for reconstructing paleofire incidence concentrations of the fungal spore sporormiella are used as a proxy for assessing large herbivore activity these proxies were tested on various modern grassland communities of the central and southern great plains including areas with bison cattle and small herbivores and areas under different fire frequencies opal phytolith assemblages and 13c values show that before cal 11 ka c3 grasses and woody plants predominated in areas that today are dominated by c4 grasses the origin of the shortgrass prairie dates back to about cal 10 ka the origin of the tallgrass prairie however is not clear as phytolith data show variable assemblages throughout the holocene mixed grass tallgrass and tallgrass woodland mosaic different proxies burnt phytoliths vs charcoal reveal different fire frequencies but it is apparent that microfossil evidence for fire incidence is closely related to the abundance of woody plants in the landscape before cal 12 ka soils show somewhat elevated concentration of sporormiella but lower concentrations than the modern high density bison and cattle grazing areas throughout the holocene sporormiella frequencies are low which suggests lower large ungulate densities and perhaps high mobility

regional aridity in north america during the middle holocene increased aridity throughout the great plains and rocky mountain region during the middle holo cene has been documented from pollen records aeolian proxy variables in lake cores and active sand dune migration varve calibration provided by a continuously varved record of the holocene from a core from elk lake northwestern minnesota shows that the influx of aeolian clastic material increased beginning about 8 ka and ended about 3 8 ka with peak aeolian activity at about 6 ka if aeolian influx to elk lake corresponds in time to aeolian influx in other lakes and to maximum dune activity in minnesota dune fields then the varve calibration in elk lake provides precise time calibration of periods of peak aeolian activity in minnesota palaeowind studies from the minnesota dune fields show that the dominant wind direction when the dunes were active was from the northwest the same as the dominant wind direction in dune fields throughout the great plains and rocky mountains if the mid holocene aeolian act

bypassing and diachronous deposition from density currents evidence from a giant regressive bed form in the poris ignimbrite tenerife canary islands exceptional longitudinal exposure through an ignimbrite sheet on the southern flanks of las canadas volcano tenerife canary islands reveals a giant regressive bed form 520 m long it comprises sourceward dipping diffuse lenses 50 m long of massive and diffuse bedded lapilli tuff its architectural relationships indicate that at any one moment in time deposition was restricted to an 50 m long longitudinal depositional zone bounded both upslope and downslope by extensive bypassing zones the regressive architecture shows that the zone of deposition gradually migrated sourceward as the current passed nonpersistent scours indicate that the current was locally and momentarily erosive although at many locations there is little evidence for substantial erosion or deposition and most of the pyroclastic load seems to have entirely bypassed subaerial slopes to enter the atlantic ocean 20 km from the source the ignimbrite is diachronous and any single vertical section through it represents only a short phase of the current9s protracted depositional history similarly protracted and complex flow histories elsewhere may be easily overlooked at typical field exposures of ignimbrites turbidites and lahar deposits leading to significantly underestimated flow durations and volumes

isotopic and geomorphic evidence for holocene climate southwestern kansas abstract the cimarron bend of southwestern kansas is characterized by loess dunes and sand sheets that reflect a complex eolian alluvial history stratigraphic evidence indicates that at least two major dune and sand sheet reactivation episodes occurred these follow intervals of alluviation stability and soil development in the holocene radiocarbon ages from paleosol horizons bracket these periods and their 13 c values provide evidence of a shift from a cooler wetter climate in the late pleistocene and early holocene dominated by c 3 plants to a warmer drier middle holocene period characterized by an increase in c 4 plants stable isotopic results for late holocene soils may reflect local rather than regional climatic conditions our results compare favorably with studies in the central and southern great plains together these results imply that a regional change toward a warmer drier climate occurred from the early to the middle holocene on the southern great plains

large scale stabilized dunes on the high plains of colorado understanding the landscape response to holocene climates with the aid of images from space principal component analysis of landsat thematic mapper images from eastern colorado reveals stabilized dune fields that are composed of single and compound parabolic dunes some longer than 10 km these dunes have been reactivated at least four times in the past 10 000 yr at ca 9500 to 5500 yr b p 5500 to gt 4800 yr b p 4800 to gt 1000 yr b p and lt 1000 yr b p during droughts that probably exceeded the dry conditions during the 1930s dune orientations indicate that these landforms were molded by winds from the northwest which now dominate during the winter and spring with the passage of pacific air masses this study underscores the sensitivity of the landscape of the high plains to drought conditions which may become more prevalent because of the anticipated effects of greenhouse warming

martian gullies a comprehensive review of observations mechanisms and insights from earth analogues upon their discovery in 2000 martian gullies were hailed as the first proof of recent i e less than a few million years flowing liquid water on the surface of a dry desert planet many processes have been proposed to have formed martian gullies ranging from liquid water seepage from aquifers melting of snow ice and frost to dry granular flows potentially lubricated by co2 terrestrial analogues have played a pivotal role in the conception and validation of gully formation mechanisms comparison with the terrestrial landscape argues for gully formation by liquid water debris flows originating from surface melting however limited knowledge of sediment transport by sublimation is a critical factor in impeding progress on the co2 sublimation hypothesis we propose avenues towards resolving the debate a laboratory simulations targeting variables that can be measured from orbit b applications of landscape evolution models c incorporation of the concept of sediment connectivity d using 3d fluid dynamic models to link deposit morphology and flow rheology and e a more intense exchange of techniques between terrestrial and planetary geomorphology including quantitative and temporal approaches finally we emphasize that the present may not accurately represent the past and that martian gullies likely formed by a combination of processes

recovery of topsoil physicochemical properties in revegetated sites in the sand burial ecosystems of the tengger desert northern china abstract recovery in soil properties and processes after sand burial in the tengger desert northern china was documented at five different aged revegetated sites 1956 1964 1973 1982 and 1991 and at a reference site with native vegetation which had never been damaged by sand burial and was enclosed for grazing the proportions of silt and clay depth of topsoil and biological soil crusts and concentrations of soil organic c k total n and total p increased with years since revegetation most characteristics of topsoil 0 5 cm characteristics had recovered to 60 of those measured at the reference site by 50 years after sand binding vegetation had been established exceptions were electrical conductivity and contents of sand silt caco 3 and organic c which recovered to 20 40 of the values at the reference site the difference in annual recovery rates of soil properties between the two most recently revegetated sites 0 14 years was greater than the difference between the two oldest revegetated sites 43 50 years best fit asymptote models showed that the estimated times for the soil properties in the 50 year old site to reach the same levels as in the reference site i e an undisturbed native steppified desert ecosystem would be between 23 and 245 years but for some properties even maximum recovery after 50 years still fell significantly short of the level at the reference site these results suggest that soil recovery is a slow process in an extremely arid desert environment and therefore the conservation of soil habitat is a crucial issue for land managers

modern and late holocene wind regimes over the great plains central u s a the great plains of the central united states contain numerous presently stabilized dune fields that were active during the late holocene the most recent period of reactivation occurred about 700 1000 years ago during the medieval climatic anomaly a period of frequent severe drought recognized throughout the north american west dune orientations and internal bedding preserve information about paleowinds from this time period we compared paleowind information with modern winds and potential sand transport analyzed from meteorological data while both reconstructed paleowinds and modern winds include a strong northwesterly component over the northern to central portions of the great plains a significant difference exists to the south during the late holocene southwesterly winds had a strong influence on dune forms over the central and southern great plains while modern potential sand transport is dominated by southerly to southeasterly winds that bring moisture to the region from the gulf of mexico hypothetical dune types forming under modern winds would be different and have different crestal orientations than those preserved from the late holocene in order for such a shift in southerly winds to take place it is likely that 1 the typical position of the bermuda high in summer was shifted either to the east or to the south resulting in weaker low level winds from the south and southeast and greater extent of southwesterly winds on the great plains and or 2 drought likely enhanced by evapotranspiration and soil moisture feedbacks brought the normally higher level southwesterly flow down to the land surface given our understanding of megadroughts over the great plains as well as recent climate predictions for increased warmth and drought over this area future reactivation of the dunes seems likely

surface morphology of caldera forming eruption deposits revealed by lidar mapping of crater lake national park oregon implications for deposition and surface modification abstract large explosive eruptions of silicic magma can produce widespread pumice fall extensive ignimbrite sheets and collapse calderas the surfaces of voluminous ignimbrites are rarely preserved or documented because most terrestrial examples are heavily vegetated or severely modified by post depositional processes much research addresses the internal sedimentary characteristics flow processes and depositional mechanisms of ignimbrites however surface features of ignimbrites are less well documented and understood except for comparatively small volume deposits of historical eruptions the 7700 calendar year b p climactic eruption of mount manama usa vented 50 km 3 of magma deposited first as rhyodacite pumice fall and then as a zoned rhyodacite to andesite ignimbrite as crater lake caldera collapsed lidar collected during summer 2010 reveals the remarkably well preserved surface of the manama ignimbrite and related deposits surrounding crater lake caldera in unprecedented detail despite forest cover the 1 m lateral and 4 cm vertical resolution lidar allows surface morphologies to be classified surface morphologies are created by internal depositional processes and can point to the processes at work when pyroclastic flows come to rest we describe nine surface features including furrow ridge sets and wedge shaped mounds in pumice fall eroded by high energy pyroclastic surges flow parallel ridges that record the passage of multiple pyroclastic flows perched benches of marginal deposits stranded by more mobile pyroclastic flow cores hummocks of dense clasts interpreted as lag deposit transverse ridges that mark the compression and imbrication of flows as they came to rest scarps indicating ignimbrite remobilization fields of closely spaced pits caused by phreatic explosions fractures and cracks due to extensional processes resulting from ignimbrite volume loss and stream channels eroded in the newly formed surface the nine morphologies presented here illustrate a dynamic depositional environment that varied spatially and with time during the eruption and show that multiple processes modified the ignimbrite after deposition both during and after the eruption

fine grained linings of leveed channels facilitate runout of granular flows abstract catastrophic dense granular flows such as occur in rock avalanches debris flows and pyroclastic flows move as fully shearing mixtures that have approximately 60 vol solids and tend to segregate to form coarse grained fronts and leveed channels levees restrict spreading of unconfined flows and form as coarse particles that become concentrated in the top of the flow are transported to the front and then advect to the sides in the flow head channels from which most material has drained away down slope are commonly lined with fine grained deposit widely thought to remain from the tail of the waning flow we show how segregation in experimental dense flows of carborundum or sand 300 425 m mixed with spherical fine ballotini 150 250 m on rough slopes of 27 29 produces fine grained channel linings that are deposited with the levees into which they grade laterally maximum runout distance is attained with mixtures containing 30 40 sand just sufficient to segregate and form levees that are adequately robust to restrict the spreading attributable to the low friction fines resin impregnation and serial sectioning of deliberately arrested experimental flows shows how fines lined levees form from the flow head the flows create their own stable conduit entirely from the front which in a geophysical context can play an important mechanistic role in facilitating runout the flow self organization ensures that low friction fines at the base of the segregated channel flow shear over fine grained substrate in the channel thus reducing frictional energy losses we propose that in pyroclastic flows and debris flows which have considerable mobility attributable to pore fluid pressures such fine grained flow contact zones form similarly and not only reduce frictional energy losses but also reduce flow substrate permeability so as to enhance pore fluid pressure retention thus the granular flow self organization that produces fine grained channel linings can be an important factor in facilitating long runout of catastrophic geophysical flows on the low slopes few degrees of depositional fans and aprons around mountains and volcanoes

interpretations and common challenges of aeolian records from north american dune fields abstract geomorphic and chronologic data for dune fields are evaluated for three contrasting areas of north america 1 the prairie parkland and boreal ecozones of the northern great plains in canada 2 the central great plains of the usa and 3 the deserts of southwestern usa and northern mexico luminescence and radiocarbon ages for periods of dune accumulation and stability are compared with palaeoenvironment proxies to provide an assessment of the boundary conditions of dune system response to changes in sediment supply availability and mobility dune fields in the northern great plains were formed from sediment originating from glaciofluvial or glaciolacustrine sediments deposited during deglaciation 16 11 ka subsequent aeolian deposition occurred in parkland and prairie dune fields as a result of mid holocene 8 5 ka and late holocene despite spatial and temporal gaps in chronometric data as a result of sampling biases the record from north american dune fields indicates the strong influence of sediment supply on dune construction with changes in sediment availability as a result of drought episodes resulting in dune field reactivation and reworking of pre existing sediment

new correlation of stable carbon isotopes with changing late holocene fluvial environments in the trinity river basin of texas usa a late holocene alluvial sequence in north central texas has a 1 m thick buried cumulic soil with an a c profile called the west fork paleosol it formed 2300 to 1000 yr bp and is a local equivalent of the copan paleosol that is present throughout the southern us great plains stable carbon isotopes indicate that the paleosol and underlying gray clay formed under vegetation dominated by c4 species mean 13c 18 3 0 3 diverse paleoenvironmental studies indicate that the period of paleosol formation was cool and wet and that alluvial water tables were high resulting in broad wet meadows across alluvial valleys characterized by communities of grasses present day wet meadows and bottomlands with mollisols with a c profiles along streams in the great plains are dominated by c4 tallgrass species and may serve as analogues to wet meadow environments during the late holocene a shift in climate to warm dry conditions about 1000 yr bp was accompanied by deep channel cutting low alluvial water tables an

grossmanite cati3 alsio6 a new pyroxene from the allende meteorite grossmanite ca ti3 mg ti4 alsio6 with an end member formula cati3 alsio6 is a new member of the ca clinopyroxene group where the trivalent cations are dominant in the m1 site with ti3 being the dominant trivalent cation it occurs as micrometer sized crystals along with spinel and perovskite in a melilite host in ca al rich refractory inclusions from the allende meteorite the mean chemical composition determined by electron microprobe analysis of the type material is wt sio2 27 99 al2o3 24 71 cao 24 58 ti2o3 10 91 tio2 6 68 mgo 4 45 sc2o3 0 43 v2o3 0 19 zro2 0 13 feo 0 08 cr2o3 0 03 sum 100 20 its empirical formula calculated on the basis of 6 o atoms is ca1 00 ti0 353 al0 18sc0 01v0 013 0 55mg0 25ti0 194 1 00 si1 07al0 93 2 00o6 grossmanite is monoclinic c 2 c a 9 80 a b 8 85 a c 5 36 a 105 62 v 447 70 a3 and z 4 its electron back scatter diffraction pattern is an excellent match to that of ti3 rich pyroxene with the c 2 c structure the five strongest calculated x ray powder diffraction lines are d spacing in a i hkl 2 996 100 221 2 964 31 310 2 581 42 002 2 600 28 131 2 535 47 221 the name is for lawrence grossman a cosmochemist at the university of chicago

discovery of dmisteinbergite hexagonal caal2si2o8 in the allende meteorite a new member of refractory silicates formed in the solar nebula dmisteinbergite caal 2si 2o 8 with p6 3 mcm structure was identified in a rounded coarse grained igneous type b2 ca al rich inclusion cai stp 1 from the allende cv3 carbonaceous chondrite stp 1 belongs to a very rare type of refractory inclusions fractionation and unknown nuclear effects fun cais which experienced melt evaporation and crystallization at low total gas pressure p 1200 c region possibly near the proto sun and were subsequently radially transported away from region possibly by a disk wind the allende dmisteinbergite occurs as irregular single crystals 100 600 m in size in contact with gehlenitic melilite and al ti diopside poikilitically enclosing euhedral spinel and rare anorthite it is colorless and transparent the mean chemical composition determined by electron microprobe analysis is wt sio 2 42 6 al 2o 3 36 9 cao 20 2 mgo 0 05 sum 99 75 giving rise to an empirical formula of ca 1 01 al 1 96 si 2 02 o 8 its electron backscatter diffraction patterns are a good match to that of synthetic caal 2si 2o 8 with the p6 3 mcm structure and the unit cell a 5 10 a c 14 72 a and z 2 dmisteinbergite could have crystallized from a silicate melt at high temperature 1200 1400 c via rapid cooling dmisteinbergite in allende the first find in a meteorite is a new member of refractory silicates among the first solid materials formed in the solar nebula

topographic controls on pyroclastic density current dynamics insight from 18 may 1980 deposits at mount st helens washington usa abstract our ability to interpret the deposits of pyroclastic density currents pdcs is critical for understanding the transport and depositional processes that control pdc dynamics this paper focuses on the influence of slope on flow dynamics and criticality as recorded in pdc deposits from the 18 may 1980 eruption of mt st helens usa pdc deposits are found along the steep flanks 10 30 and across the pumice plain 5 up to 8 km north of the volcano granulometry componentry and descriptions of depositional characteristics e g bedform morphology are recorded with distance from source the pumice plain deposits are primarily thick 3 12 m massive and poorly sorted and represent deposition from a series of concentrated pdcs by contrast the steep flank deposits are stratified to cross stratified suggesting deposition from pdcs where turbulence strongly influenced transport and depositional processes we propose that acceleration of the concentrated pdcs along the steep flanks resulted in thinning of the concentrated basal region of the current s enhanced entrainment of ambient air and autofluidization from upward fluxes of air from substrate interstices and plunging breakers across rugged irregular topography further inflated the currents to the point that the overriding turbulent region strongly influenced transport and depositional mechanisms acceleration in combination with partial confinement in slot canyons and high surface roughness would also increase basal shear stress further promoting shear and traction transport in the basal region of the current conditions along the steep flank resulted in supercritical flow as recorded by regressive bedforms which gradually transitioned to subcritical flow downstream as the concentrated basal region thickness increased as a function of decreasing slope and flow energy we also find that 1 pdcs were erosive into the underlying granular substrate along high slopes 25 where currents were partially confined in steep slot canyons suggesting that basal shear stress is an important control on erosive capacity and 2 bedform amplitude wavelength and the presence of regressive bedforms increase with increasing slope and proximity to source along the steep flank suggesting a link between bedform morphology flow velocity and flow criticality while our results indicate that slope and irregular topography strongly influence pdc dynamics criticality and erosive capacity the influence of these conditions on ultimate flow runout distance is unclear the work here also highlights the issue that relationships between the controls on bedform size and morphology in density stratified flows remain poorly constrained limiting our ability to extract important information about the currents that produced them these final two points warrant further exploration through the combination of field experimental and numerical approaches

granular fingering as a mechanism for ridge formation in debris avalanche deposits laboratory experiments and implications for tutupaca volcano peru the origin of subparallel regularly spaced longitudinal ridges often observed at the surface of volcanic and other rock avalanche deposits remains unclear we addressed this issue through analogue laboratory experiments on flows of bi disperse granular mixtures because this type of flow is known to exhibit granular fingering that causes elongated structures resembling the ridges observed in nature we considered four different mixtures of fine 300 400 m glass beads and coarse 600 710 m to 900 1000 m angular crushed fruit stones with particle size ratios of 1 9 2 7 and mass fractions of the coarse component of 5 50 wt the coarse particles segregated at the flow surface and accumulated at the front where flow instabilities with a well defined wavelength grew these formed granular fingers made of coarse rich static margins delimiting fines rich central channels coalescence of adjacent finger margins created regular spaced longitudinal ridges which became topographic highs as finger channels drained at final emplacement stages three distinct deposit morphologies were observed 1 joined fingers with ridges were formed at low 1 9 size ratio and moderate 10 20 wt coarse fraction whereas 2 separate fingers or 3 poorly developed fingers forming series of frontal lobes were created at larger size ratios and or higher coarse contents similar ridges and lobes are observed at the debris avalanche deposits of tutupaca volcano peru suggesting that the processes operating in the experiments can also occur in nature this implies that volcanic and non volcanic debris avalanches can behave as granular flows which has important implications for interpretation of deposits and for modeling such behaviour may be acquired as the collapsing material disaggregates and forms a granular mixture composed by a right grain size distribution in which particle segregation can occur limited fragmentation and block sliding or grain size distributions inappropriate for promoting granular fingering can explain why ridges are absent in many deposits

decoding pyroclastic density current flow direction and shear conditions in the flow boundary zone via particle fabric analysis abstract one of the greatest challenges in volcanology is extracting information from volcanic deposits that inform the conditions at the time of emplacement here we explore particle shape fabric within samples from the column collapse pyroclastic density current pdc deposits generated by the 18 may 1980 eruption of mt saint helens msh particle shape fabric is the mutual alignment of particles within a sample which is dependent on shearing conditions at the time of deposition here particle shape fabric is used to address the following hypotheses 1 particle shape fabric will align with bulk flow direction estimates made by previous studies while resolving fine scale flow direction variations 2 samples extracted from pdc deposits immediately above a basal contact will show higher extents of fabric development i e clast alignment relative to samples extracted well above the contact and 3 samples extracted from cross stratified deposits will have higher extents of fabric development relative to samples extracted from the massive facies we find that fabric orientations approximate previous flow direction interpretations of general flow from south to north and channelization due to paleo topography furthermore shape fabric records flow interaction with the substrate created by debris avalanche deposits leading to fine scale variations in flow paths these variations are recorded in samples extracted near the substrate deposit contact moreover these samples do not show a higher measure of clast alignment relative to samples taken well above flow contacts but do exhibit bimodal clast alignment this suggests some degree of traction transport and thus higher shearing conditions relative to when the currents deposited massive lapilli tuffs samples extracted from the cross stratified deposits do not show higher extents of fabric development relative to the massive deposits supporting previous interpretations that these deposits formed from a rapidly sedimenting concentrated flow boundary zone that was thin enough to be frequently interrupted or influenced by the overriding turbulent portion of the flow finally observations of fine scale variability in measured fabric within a single outcrop indicates unsteady flow conditions and step wise aggradation during deposition this work demonstrates that particle shape fabric analyses can aid in decoding pdc flow conditions future complementary experimental work may allow for the extraction of quantitative information regarding the magnitudes of shear and subsequent particle alignments within the flow boundary zone providing further insight into pdc dynamics

late holocene aeolian activity in the cimarron river valley of west central oklahoma abstract this investigation uses a multidisciplinary approach including geomorphic surface mapping soil stratigraphic analysis radiocarbon dating and optically stimulated luminescence osl dating to investigate the chronology of soil formation and aeolian activation periods recorded in ridge dune deposits as well as the spatial variability of aeolian processes during active aeolian episodes this study shows that aeolian landforms superimposed on fluvial terraces adjacent to the cimarron river in southeastern major county and northwestern kingfisher county oklahoma are the product of distinct late holocene climatic conditions in which periods of dune activity are episodic and accumulation of sediments is relatively rapid soil forming processes operated on the stabilized dunes during intervening periods we also demonstrate that the synthesis of geomorphic techniques soil stratigraphy 14c dating and osl dating can provide complimentary and high resolution data about aeolian activity in the southern plains

fluvial response to precipitation variations since 36 ka in the hunshandake sandy land in north china abstract the hunshandake sandy land which is highly sensitive to climate change is located in north china along the margins of the area influenced by the east asian monsoon the upper reach of the xilamulun river which drains the hunshandake sandy land provides an opportunity to test the response of a river landform within a sandy region to climate change we investigated terraces at 4 sites along a 38 km long stretch and performed osl dating on 26 terraces the dating results revealed 23 terraces with unsaturated ages ranging from 0 3 ka to 36 2 ka the observed relationship between the terrace heights and ages is abnormal i e the terrace age does not increase with the terrace height in this case aeolian and fluvial interactions were analyzed and a precipitation dominated terrace formation model was developed higher terraces formed when the riverbed aggraded due to decreased sediment discharge and increased aeolian sand input during a period of reduced precipitation in contrast lower terraces developed when the riverbed eroded during a period of enhanced precipitation we conclude that the terraces along this hunshandake sandy land river respond to precipitation changes even in the absence of background uplift

late holocene dune migration on the south texas sand sheet abstract there are a wide variety of vegetated eolian depositional landforms associated with the south texas sand sheet attesting to the past dominance of eolian processes mapping identified two sets of parabolic dunes elongating with winds from the southeast and the northwest parabolic dunes elongated by northwesterly winds are older than ca 200 years and may be associated with eolian depositional events ca 2700 and or 2000 years ago the latest dune migration event associated with southeasterly winds occurred ca 200 years ago and at one site is inset into northwesterly extended parabolic dunes this period of dune migration may be coincident with particularly severe drought identified in the tree ring record centered at ad 1790 when the palmer drought severity index was 4 a threshold of dune movement may have occurred ca in the 11th 15th and 20th centuries when there are two or more consecutive years with a palmer drought severity index of

mineralogy and environmental geochemistry of historical iron slag hopewell furnace national historic site pennsylvania usa the hopewell furnace national historic site in southeastern pennsylvania which features an fe smelter that was operational in the 18th and 19th centuries is dominated by three slag piles pile 1 slag from the hopewell furnace and pile 2 slag likely from the nearby cornwall furnace were both produced in cold blast charcoal fired smelters in contrast pile 3 slag was produced in an anthracite furnace ore samples from the nearby jones and hopewell mines that fed the smelter are mainly magnetite rich with some sulfides pyrite chalcopyrite sphalerite and accessory silicates quartz garnet feldspar and clay minerals slag piles 1 and 2 are similar mineralogically containing predominantly skeletal and dendritic aluminian diopside and augite skeletal forsteritic olivine glass rounded blebs of metallic fe and exotic quartz olivine is a major phase in all samples from pile 2 whereas it occurs in only a few samples from pile 1 samples of the 2 mm size fraction of surface composite slag material or crushed slag from at depth in piles 1 and 2 are mineralogically similar to the large surface slag fragments from those piles with the addition of phases such as feldspars fe oxides and clay minerals that are either secondary weathering products or entrained from the underlying bedrock pile 3 slag contains mostly skeletal forsteritic olivine and ti bearing aluminian diopside dendritic or fine grained subhedral melilite glass euhedral spinel metallic fe alabandite oldhamite solid solution as well as a sparse ti carbonitride phase the bulk chemistry of the slag is dominated by al2o3 8 5 16 2 wt cao 8 2 26 2 wt mgo 4 2 24 7 wt and sio2 36 4 59 8 wt constituting between 81 and 97 of the mass of the samples piles 1 and 2 are chemically similar pile 1 slag overall contains the highest fe2o3 k2o and mno and the lowest mgo concentrations pile 3 slag is high in al2o3 cao and s and low in fe2o3 k2o and sio2 compared to the other piles in general piles 1 and 2 are chemically similar to each other whereas pile 3 is distinct a conclusion that reflects their mineralogy the similarities and differences among piles in terms of mineralogy and major element chemistry result from the different smelting conditions under which the slag formed and include the fuel source the composition of the ore and flux the type of blast cold versus hot which affects the furnace temperature and other beneficiation methods the three distinct slag piles at hopewell are enriched in numerous trace elements such as as up to 12 mg kg cd up to 0 4 mg kg co up to 31 8 mg kg cu up to 647 mg kg mn up to 0 69 wt pb up to 172 mg kg and zn up to 393 mg kg together with fe 13 9 wt when compared to the average for the continental crust with the 2 mm size fraction commonly containing the highest concentrations enrichments in various elements e g cd co cu pb zn were also found in the ore samples despite these enrichments comparison of bulk chemistry trace element concentrations to the environmental guidelines suggests most elements are likely not problematic with the exception of as co fe and mn leachate tests that simulate weathering indicate fe up to 973 g l and mn up to 133 g l are readily released in potentially harmful concentrations compared to secondary drinking water and some aquatic ecosystem toxicity criteria aluminum and cu although not high in the solid compared to environmental guidelines also exceed relevant criteria in leachate extracts with maximum concentrations of 2700 g l and 17 7 g l respectively in contrast as and co which are significant in the solids are not leached in concentrations that exceed guidelines i e 3 g l or less for both elements the weathering rates of the fe metal and fe oxides which host cu and some fe are likely higher than the silicate glass which hosts the majority of al mn and some fe and the crystalline silicates and spinels affecting which elements and how much are released into the environment and surrounding aquatic ecosystem the mineral assemblages and their chemical composition the bulk sample chemistry and leachability of trace elements are all important components in understanding the potential environmental impacts of the slag piles

how many boron minerals occur in earth s upper crust the current rate of discovery of new boron minerals 65 species or potential species described from 2008 to 2017 is higher than at any prior 10 year period implying that rates of b mineral discovery could increase further with no obvious limit to boron mineral diversity in earth s crust in contrast large number of rare events lnre models calculated from the 295 species of b minerals discovered through 2017 give a total predicted b mineral endowment in earth s crust of 459 65 5 and 523 species using a finite zipf mandelbrot fzm model and sichel s generalized inverse gauss poisson model gigp respectively i e there is a very real predicted limit of no more than 500 species as cautioned by hazen hystad and their co authors lnre modeling presumes no changes in how minerals are discovered from the beginning of mineral discoveries in the late 18th century to early 2017 however this condition is clearly not the case and thus changes could explain the discrepant indications the most important changes are 1 the advent of the electron microprobe which became widely used for chemical analysis of b minerals in 1978 2 technological advances in single crystal x ray diffractrometry 3 technological advances in electron microscopy including advent of electron backscattered diffraction 4 advent of micro raman spectroscopy and 5 changes in mineralogical nomenclatures particularly of the tourmaline supergroup changes 1 to 4 are expected to reduce the size of the mineral grains that can be studied thereby increasing the number of species accessible to study furthermore should species have a fractal distribution i e diversity is independent of scale examination of increasingly smaller grains will turn up an even larger number of species to evaluate the impact of these changes on the lnre modeling we modeled the 146 b minerals discovered up through 1978 which was selected as the cutoff because of 1 the important role played subsequently by the electron microprobe and 2 the number of species was 50 of the current number this modeling gave 306 fzm and 359 gigp for total species i e the access to smaller grains afforded by advanced analytical instrumentation has resulted in an increased estimate of total endowment by 50 from 1978 whether the fzm or gigp distribution is applied we doubt that the 500 b species estimate is the end of the story as we expect there will be further technological advances in the future a more realistic finale might come when we reach the natural limit imposed by the minimum number of unit cells needed for new mineral to be viable and thus lnre modeling might yet show that earth s total endowment of b minerals is finite a review of past patterns of discovery of new boron minerals which can inform us what to expect in future discoveries reveal that only 19 of b minerals were synthesized prior to discovery we conclude that synthetic compounds are not a particularly promising source of potential new b minerals in contrast 22 of b minerals were discovered prior to synthesis and 29 have unique structures i e they have no synthetic analogs and are not isostructural with a known mineral accordingly 41 of b minerals could not be predicted and we conclude that the realm of as yet undiscovered b minerals holds a significant number of surprises

the kinematics of bidisperse granular roll waves small perturbations to a steady uniform granular chute flow can grow as the material moves downslope and develop into a series of surface waves that travel faster than the bulk flow this roll wave instability has important implications for the mitigation of hazards due to geophysical mass flows such as snow avalanches debris flows and landslides because the resulting waves tend to merge and become much deeper and more destructive than the uniform flow from which they form natural flows are usually highly polydisperse and their dynamics is significantly complicated by the particle size segregation that occurs within them this study investigates the kinematics of such flows theoretically and through small scale experiments that use a mixture of large and small glass spheres it is shown that large particles which segregate to the surface of the flow are always concentrated near the crests of roll waves there are different mechanisms for this depending on the relative speed of the waves compared to the speed of particles at the free surface as well as on the particle concentration if all particles at the surface travel more slowly than the waves the large particles become concentrated as the shock like wavefronts pass them this is due to a concertina like effect in the frame of the moving wave in which large particles move slowly backwards through the crest but travel quickly in the troughs between the crests if instead some particles on the surface travel more quickly than the wave and some move slower then at low concentrations large particles can move towards the wave crest from both the forward and rearward sides this results in isolated regions of large particles that are trapped at the crest of each wave separated by regions where the flow is thinner and free of large particles there is also a third regime arising when all surface particles travel faster than the waves which has large particles present everywhere but with a sharp increase in their concentration towards the wave fronts in all cases the significantly enhanced large particle concentration at wave crests means that such flows in nature can be especially destructive and thus particularly hazardous

hutcheonite ca3ti2 sial2 o12 a new garnet mineral from the allende meteorite an alteration phase in a ca al rich inclusion hutcheonite ima 2013 029 ca 3ti 2 sial 2 o 12 is a new garnet mineral that occurs with monticellite grossular and wadalite in secondary alteration areas along some cracks between primary melilite spinel and ti al diopside in a type b1 fractionation and unidentified nuclear effects fun ca al rich inclusion cai egg 3 from the allende cv vigarano type carbonaceous chondrite the mean chemical composition of type hutcheonite by electron probe microanalysis is wt cao 34 6 tio 2 25 3 sio 2 20 9 al 2o 3 15 7 mgo 2 1 feo 0 7 v 2o 3 0 5 total 99 8 giving rise to an empirical formula of ca 2 99 ti 4 1 53 mg 0 25 al 0 17 fe 2 0 05 v 3 0 03 si 1 68 al 1 32 o 12 the end member formula is ca 3ti 2 sial 2 o 12 hutcheonite has the ia3d garnet structure with a 11 843 a v 1661 06 a 3 and z 8 as revealed by electron backscatter diffraction the calculated density using the measured composition is 3 86 g cm 3 hutcheonite is a new secondary phase in allende apparently formed by iron alkali halogen metasomatic alteration of the primary cai phases like melilite perovskite and ti al diopside on the cv chondrite parent asteroid formation of the secondary ti rich minerals like hutcheonite during the metasomatic alteration of the allende cais suggests some mobility of ti during the alteration the mineral name is in honor of ian d hutcheon a cosmochemist at lawrence livermore national laboratory california u s a

the controls and consequences of substrate entrainment by pyroclastic density currents at mount st helens washington usa evidence in the deposits from the may 18 1980 eruption at mount st helens demonstrates that pyroclastic density currents pdcs produced during the afternoon of the eruption became intermittently erosive using detailed componentry and granulometry we constrain the sources for lithic blocks in the deposits and identify deposits from pdcs that became locally erosive the componentry of the lithics in the fall deposits is used as a proxy for vent erosion and assumed to represent the starting componentry for pdcs prior to entrainment from any other source we find little evidence in the pdc deposits nearest to the base of the volcano for entrainment from the steep flanks however significant evidence indicates that pdcs eroded into the debris avalanche hummocks suggesting that entrainment is favored as pdcs interact with highly irregular topography evidence for locally entrained material downstream from debris avalanche hummocks decreases with height in the outcrop suggesting that less entrainment occurs as local relief decreases and upstream topography is buried the prevalence of lithofacies containing locally entrained material at the base of unit contacts and only 10s of meters downstream from debris avalanche hummocks suggests that the majority of entrainment occurs at or near the head of the current occasionally entrained material is located high above unit contacts and deposited well after the initial head of the current is inferred to have passed indicating that entrainment can occur during periods of non deposition either from the semi sustained body of the current or from a pulsating current additionally self channelization of pdcs either by levee deposition or scouring into earlier pdc deposits occurs independently of interaction with topographic obstacles and can affect carrying capacity and runout distance while we begin to explore the mechanisms and effects of erosion on current dynamics additional laboratory and numerical studies are necessary to fully understand these processes

deconstructing aeolian landscapes abstract semi stabilized dune systems are important indicators of quaternary drought variability across central north america the south texas sand sheet stss is the southernmost relict dune system on the great plains and is exposed to higher evapotranspiration and moisture variability than similar landscapes farther north in this study a combination of surface and sub surface remote sensing is used to analyze the semi stabilized dune landscapes of the stss in order to delineate distinct aeolian sediments that can represent generations of sedimentation or particular climate conditions the combination of multi resolution analysis of a lidar dataset electromagnetic conductivity surveys and xrf scans of soil cores are shown to be useful tools for deconstructing and modeling the environmental history of the stss optically stimulated luminescence osl dating of identified surfaces suggests that the stss is older than previously thought since dune systems are excellent repositories of climate and biophysical data for a landscape and are also sensitive to changes in climate and ecology the methodology employed in this study can be used to characterize the vulnerability of other similar environments to climate change through the holocene and over the next century

middle and late holocene dune reactivation in the nebraska sand hills usa a combination of optical dating of aeolian sand and radiocarbon dating of palaeosols and interdune sediments has allowed some refinements to the chronostratigraphy of the nebraska sand hills our results directly confirm previous inferences that multiple phases of aeolian deposition including megabarchan dune reactivation occurred within the sand hills during the middle and late holocene optical dates on stratified aeolian barchan dune sediments from two localities provide ages ranging from c 6 ka to 300 years ago weakly developed palaeosols intercalated within the dune sediments and other forms of post depositional modification indicate periods of relative stability and reduced dune mobilization optical dates on the upper 12 15 m of two dune exposures indicate repeated possibly regionally correlative reactivations which occurred between c 400 500 and 200 300 years ago comparison of late holocene aeolian activity with local and regional palaeoclimatic proxy records suggests that dune reacti

the perfect debris flow aggregated results from 28 large scale experiments 1 aggregation of data collected in 28 controlled experiments reveals reproducible debris flow behavior that provides a clear target for model tests in each experiment 10 m3 of unsorted water saturated sediment composed mostly of sand and gravel discharged from behind a gate descended a steep 95 m flume and formed a deposit on a nearly horizontal runout surface experiment subsets were distinguished by differing basal boundary conditions 1 versus 16 mm roughness heights and sediment mud contents 1 versus 7 percent dry weight sensor measurements of evolving flow thicknesses basal normal stresses and basal pore fluid pressures demonstrate that debris flows in all subsets developed dilated coarse grained high friction snouts followed by bodies of nearly liquefied finer grained debris mud enhanced flow mobility by maintaining high pore pressures in flow bodies and bed roughness reduced flow speeds but not distances of flow runout roughness had these effects because it promoted debris agitation and grain size segregation and thereby aided growth of lateral levees that channelized flow grain size segregation also contributed to development of ubiquitous roll waves which had diverse amplitudes exhibiting fractal number size distributions despite the influence of these waves and other sources of dispersion the aggregated data have well defined patterns that help constrain individual terms in a depth averaged debris flow model the patterns imply that local flow resistance evolved together with global flow dynamics contradicting the hypothesis that any consistent rheology applied we infer that new evolution equations not new rheologies are needed to explain how characteristic debris flow behavior emerges from the interactions of debris constituents

erosional characteristics and behavior of large pyroclastic density currents factors influencing the erosive behavior of large pyroclastic density currents pdcs both mainly massive and thinly stratified are not well understood to investigate the parameters influencing the erosive behavior of pdcs produced during the flowing phase of large caldera forming plinian campanian ignimbrite and phreatoplinian neapolitan yellow tuff eruptions we use scoured fall deposits at the base of or interstratified with pdc deposits from the campanian region of italy at several localities we calculated the depth of pdc erosion by comparing the measured thickness of eroded remnants to reconstructed thickness at each site estimated by isopach mapping and recorded the 1 distance from vent 2 elevation of the locality and 3 paleoslopes furthermore we have considered how these factors can be influenced by outcrop exposure depth of erosion correlates with distance from the vent in low relief landscape while across very rugged topography the only related parameter is elevation the different erosive patterns appear to show how pyroclastic currents interact with the topography in the surrounding terrain when a pdc crosses relatively flat surfaces it decelerates away from the vent decreasing its erosive capacity but when moving through steep terrain a pdc accelerates down the valley increasing its erosive capacity

enhanced mobility of granular mixtures of fine and coarse particles understanding how granular materials flow remains an outstanding issue in both nature and industry where typically a range of particle sizes are involved we present laboratory measurements of flows of binary mixtures of fine and coarse granular materials that show that their interaction can result in significantly increased mobility the ratio of the run out distance for the centre of mass to the initial height of the centre of mass at a fine material mass fraction the ratio of the mass of fine particles to the total mass of the flow of about 0 3 the flow mobility can be increased by up to a factor of 4 compared with the same mass of either all fine or all coarse material measurements of the distribution of the deposited fine and coarse particles along the length of the flow show that in low mobility flows the peak in deposition of fine and coarse particles occurs at different positions whereas for high mobility flows there is a more uniform deposition of both particle sizes we interpret the observations of flow mobility in terms of two primary mechanisms at low the fine particles lubricate the flow of the coarse particles by rolling whereas at high the presence of coarse particles reduces the inter particle frictional losses in the flow we use heuristic models to illustrate that these mechanisms are likely to occur in granular flows containing a wide range of grain sizes noting that the detailed physical descriptions and mathematical models of these particle interactions are currently incomplete these experimental observations challenge the traditional view that the extent of geophysical granular flows depends on their volume in line with other recent studies of slumping granular materials recent studies which use a single particle size show strong dependence of flow run out on the initial aspect ratio of the release our results suggest that compositional effects in flows containing more than one particle size may be at least as important

stable carbon isotopes c3 c4 vegetation and 12 800years of climate change in central new mexico usa abstract a thick sequence of fine textured alluvium in central new mexico has provided an opportunity to reconstruct vegetation type and climate at the western edge of the great plains grassland the analysis of thirty eight ams radiocarbon ages 13 c values and modern weather data has produced a 12 800 cal yr record of changing c 3 c 4 vegetation temperature and precipitation the record begins with the younger dryas that was characterized by c 3 plants and was about 2 4 c cooler with over 100 mm rainfall than today after 11 000 cal yrs bp the climate became less cool and less wet reaching present day conditions by 9000 yrs the middle holocene was c 4 warm and dry although the 13 c record is incomplete for this interval from 3300 to 1400 cal yrs bp the climate was cool and wet with c 3 plants averaging 0 5 c cooler and 22 mm greater rainfall than today matching other records in the region for a wetter climate after 1400 cal yrs bp the local climate became warm and dry shifting to c 4 vegetation the severe second century drought first observed in tree rings in southern colorado is supported by the 13 c data and occurred during the interval a d 40 to a d 180 hiatuses in the local alluvial and 13 c record extend from 9000 to 6000 cal yrs bp and from 1000 cal yrs bp to present

relation between dry granular flow regimes and morphology of deposits formation of levees in pyroclastic deposits experiments on dry granular matter flowing down an inclined plane are performed in order to study the dynamics of dense pyroclastic flows the plane is rough and always wider than the flow focusing this study on the case of laterally unconfined free boundary flows we found that several flow regimes exist depending on the input flux and on the inclination of the plane each flow regime corresponds to a particular morphology of the associated deposit in one of these regimes the flow reaches a steady state and the deposit exhibits a levee channel morphology similar to those observed on small pyroclastic flow deposits the levees result from the combination between lateral static zones on each border of the flow and the drainage of the central part of the flow after the supply stops particle segregation features are created during the flow corresponding to those observed on the deposits of pyroclastic flows moreover the measurements of the deposit morphology thickness of the channel height of the levees width of the deposit are quantitatively related to parameters of the dynamics of the flow flux velocity height of the flow leading to a way of studying the flow dynamics from only measurements of the deposit some attempts to make extensions to natural cases are discussed through experiments introducing the polydispersity of the particle sizes and the particle segregation process

erosion transport and segregation of pumice and lithic clasts in pyroclastic flows inferred from ignimbrite at lascar volcano chile abstract investigations have been made on the distribution of pumice and lithic clasts in the lithic rich soncor ignimbrite 26 5 ka and the 1993 pumice flow deposits of lascar volcano chile the soncor ignimbrite shows three main lithofacies which grade into one another coarse lithic breccias range from matrix poor stratified varieties irregular shaped sheets and elongate hummocks in proximal environments to breccia lenses with pumiceous ignimbrite matrix massive lithic rich facies comprise the bulk of the ignimbrite pumice rich facies are bimodal with abundant large pumice clasts often with reverse grading rare lithic clasts and occur distally and on high ground adjacent to deep proximal valleys in the 1993 pyroclastic flow deposits lithic rich facies are deposited on slopes up to 14 whereas pumice rich facies are deposited only on slopes

late quaternary eolian sand depositional record for southwestern kansas landscape sensitivity to droughts abstract eolian deposits and landforms are ubiquitous in western kansas particularly south of the arkansas river with the presence of a stabilized dune field stratigraphic studies and associated optical dating reveal a complex depositional history for this dune field spanning the late quaternary the oldest eolian deposits from ca 16 to 12 ka completely or partially bury high terraces with ages of ca 16 and 33 ka it is unknown whether these eolian deposits reflect regional aridity and or a change in sediment availability with the transition of the arkansas river from a single channel to a braided system there is pervasive evidence for episodic eolian erosion and deposition ca 9 8 to 6 3 ka generally coincident with loess deposition on upland surfaces olson c g nettleton w d porter d a brasher b r 1997 middle holocene aeolian activity on the high plains of west central kansas holocene 7 3 255 261 and thus it is inferred to reflect regional aridity sites within the dune field show a sequence of eolian sands and weak buried soils reflecting either dune migration or sand sheet accretion at ca 1490 430 380 320 180 and 70 yr ago which correspond well with continental scale droughts in the tree ring record eolian sand in the arkansas river dune field may be derived principally with variability in fluvial activity and in climate during the late pleistocene to the middle holocene with substantial reactivation of eolian systems during decadal scale drought variability in the past 2000 yr

mineralogical anatomy and implications of a ti sc rich ultrarefractory inclusion from sayh al uhaymir 290 ch3 chondrite titanium rich minerals are common in ca al rich inclusions from primitive chondrites they are important not only for testing the condensation models for a gas with a solar composition but also for constraining the redox conditions of the early solar nebula in this study we report the detailed mineralogical features and its oxygen isotope compositions of a ti sc rich ultrarefractory inclusion a0031 from a ch3 chondrite sayh al uhaymir 290 the a0031 inclusion has a compact and layered texture with the interior consisting of panguite sc rich anosovite ti rich davisite and anorthite a few hexaferrum perovskite and spinel crystals are present as inclusions in these minerals outside of ti rich davisite are a layer of al ti rich diopside and two grains of enstatite this texture strongly suggests that a0031 has a condensation origin panguite is its third occurrence in nature and similar in composition to the type panguite from the allende meteorite sc rich anosovite in a0031 has a chemical formula of ti 4 ti 3 mg sc al 3o 5 with the pseudobrookite structure this is the second report of ti 3o 5 in nature but is the first description of anosovite formed in the solar nebula as an ultrarefractory phase the discovery of sc rich anosovite in a0031 reveals the stability of ti 3o 5 in the early solar nebula and supports the prediction of previous equilibrium condensation calculations the panguite sc rich anosovite and ti rich davisite in a0031 show a large variation in ti 3 ti tot the primitive nature of a0031 implies that the variations in ti 3 ti tot among different ti rich minerals are primary features we propose that the distribution of ti 3 and ti 4 could be controlled mainly by their various competition abilities of incorporating into these ti sc al rich minerals similarity of ti 3 ti tot value between ti rich davisite from a0031 and those in other carbonaceous chondrites indicates that most refractory inclusions might have formed in highly reducing nebular settings the 16 o depleted isotope compositions of a0031 confirm the existence of diverse oxygen reservoirs for ch ca al rich inclusions in the solar nebula

inviscid behaviour of fines rich pyroclastic flows inferred from experiments on gas particle mixtures abstract experiments were carried out on granular flows generated by instantaneous release of gas fluidised bidisperse mixtures and propagating into a horizontal channel the mixture consists of fine 100 m particles of same density with corresponding grain size ratios of 2 to 9 initial fluidisation of the mixture destroys the interparticle frictional contacts and the flow behaviour then depends on the initial bed packing and on the timescale required to re establish strong frictional contacts at a fines mass fraction below that of optimal packing 40 the initial mixtures consist of a continuous network of coarse particles with fines in interstitial voids strong frictional contacts between the coarse particles are probably rapidly re established and the flows steadily decelerate some internal friction reduction appears to occur as and the grain size ratio increases possibly due to particle rolling and the lower roughness of internal shear surfaces segregation only occurs at large grain size ratio due to dynamical sieving with fines concentrated at the flow base in contrast at above that for optimal packing the initial mixtures consist of coarse particles embedded in a matrix of fines flow velocities and run outs are similar to that of the monodisperse fine end member thus showing that the coarse particles are transported passively within the matrix whatever their amount and grain size are these flows propagate at constant height and velocity as inviscid fluid gravity currents thus suggesting negligible interparticle friction we have determined a froude number of 2 61 0 08 consistent with the dam break model for fluid flows and with no significant variation as a function of the grain size ratio and the initial bed expansion very little segregation occurs which suggests low intensity particle interactions during flow propagation and that active fluidisation is not taking place strong frictional contacts are only re established in the final stages of emplacement and stop the flow motion we infer that fines rich i e matrix supported pyroclastic flows propagate as inviscid fluid gravity currents for most of their emplacement and this is consistent with some field data

geomorphic and sedimentary responses of the bull creek valley southern high plains usa to pleistocene and holocene environmental change abstract fluvial geomorphology and stratigraphy often reflect past environmental and climate conditions this study examines the response of bull creek a small ephemeral creek in the oklahoma panhandle to environmental conditions through the late pleistocene and holocene fluvial terraces were mapped and their stratigraphy and sedimentology documented throughout the course of the main valley based on their elevations terraces were broadly grouped into a late pleistocene fill terrace t3 and two holocene fill cut terrace sets t2 and t1 terrace systems are marked by similar stratigraphies recording the general environmental conditions of the time sedimentary sequences preserved in terrace fills record the transition from a perennial fluvial system during the late glacial period and the younger dryas to a semiarid environment dominated by loess accumulation and punctuated by flood events during the middle to late holocene the highest rates of aeolian accumulation within the valley occurred during the early to middle holocene our data provide significant new information regarding the late pleistocene and holocene environmental history for this region located between the well studied southern and central high plains of north america

new views of granular mass flows concentrated grain fluid mixtures in rock avalanches debris flows and pyroclastic flows do not behave as simple materials with fixed rheologies instead rheology evolves as mixture agitation grain concentration and fluid pressure change during flow initiation transit and deposition throughout a flow however normal forces on planes parallel to the free upper surface approximately balance the weight of the superincumbent mixture and the coulomb friction rule describes bulk intergranular shear stresses on such planes pore fluid pressure can temporarily or locally enhance mixture mobility by reducing coulomb friction and transferring shear stress to the fluid phase initial conditions boundary conditions and grain comminution and sorting can influence pore fluid pressures and cause variations in flow dynamics and deposits

amoeboid olivine aggregates aoas in the efremovka leoville and vigarano cv3 chondrites a record of condensate evolution in the solar nebula abstract amoeboid olivine aggregates aoas in the efremovka leoville and vigarano cv3 chondrites were studied using petrographic and microanalytical techniques to evaluate the origins of these inclusions and their relationships to other chondrite components our data support the idea that the inclusions formed by dust growth in the solar nebula as condensates and that they preserve a record of mineralogical and chemical evolution spinel rich nodules and ribbons in aoas often show group ii trace element patterns and formed either by fractional condensation or by condensation following partial vaporization the dominant olivine component in aoas can be explained as a condensate produced in the same way but with fractionation occurring at a lower temperature other spinel rich material in aoas appears to be a vaporization residue ca rich pyroxene anorthite patches in aoas show chemical signatures similar to those observed for spinel or melilite bearing regions but with lower refractory element and higher mg and si contents supporting the idea that the patches formed by reaction between cai like material and mg si rich gas different trace element patterns group ii and non group ii refractory are sometimes found for al rich regions ca pyroxene anorthite or melilite bearing in a given aoa suggesting that aoas agglomerated from materials that formed under different conditions and that they did not subsequently homogenize aoas appear to have originated in a system with near canonical solar composition and a low pressure gas 10 6 10 4 bar over a range of temperatures mainly 1200 1384 k under somewhat non equilibrium conditions relative to predicted equilibrium condensates most aoas show an apparent paucity of metal possibly reflecting differential density dependent sorting between olivine and metal grains during aggregate formation trace element data are consistent with a simple model involving melting and igneous fractionation of aoa like olivine to produce type i chondrule olivine but other data suggest that open system melting of chondrules occurred in a different gaseous environment than that which produced aoas

origin of compact type a refractory inclusions from cv3 carbonaceous chondrites compact type a cta inclusions are one of the major types of coarse grained refractory inclusions found in carbonaceous chondrites they have not been studied in a systematic fashion leading to some uncertainties and unproven assumptions about their origin to address this situation we studied a total of eight ctas from allende efremovka and axtell by scanning electron microscopic and electron and ion microprobe techniques these inclusions are very melilite rich ranging from 60 vol to nearly monomineralic also present are mg al spinel 5 20 perovskite trace 3 and in some samples ti rich 17 wt tio2tot fassaite trace 20 and rhonite 1 melilite compositions are mostly between ak15 and ak40 chondrite normalized ree abundance patterns for melilite flat at 10 ci with positive eu anomalies and fassaite slight hree enrichment relative to lree and negative eu anomalies are like those for their counterparts in once molten type b inclusions the patterns for rhonite have positive slopes from la through lu and abundances 10 ci for la and 35 60 ci for lu features of ctas that suggest that they were once molten include rounded inclusion shapes positively correlated sc and v abundances in fassaite radially oriented melilite laths at inclusion rims and the distribution of trace elements among the phases fractional crystallization models show that with one exception the ree contents of perovskite and fassaite arose by crystallization of these phases from late residual liquids that would have resulted from prior crystallization of the observed proportions of melilite and spinel from liquids having the bulk compositions of the inclusions one allende cta ts32 however has several features irregular shape reversely zoned melilite fassaite ree contents that are not readily explained by crystallization from a melt this inclusion may have undergone little melting and may be dominated by relict grains

pyroclastic flows generated by gravitational instability of the 1996 97 lava dome of soufriere hills volcano montserrat numerous pyroclastic flows were produced during 1996 97 by collapse of the growing andesitic lava dome at soufriere hills volcano montserrat measured deposit volumes from these flows range from 0 2 to 9 106 m flows range from discrete single pulse events to sustained large scale dome collapse events flows entered the sea on the eastern and southern coasts depositing large fans of material at the coast small runout distance 1 km flows had average flow front velocities in the order of 3 10 m s while flow fronts of the larger runout distance flows up to 6 5 km advanced in the order of 15 30 m s many flows were locally highly erosive field relations show that development of the fine grained ash cloud surge component was enhanced during the larger sustained events periods of elevated pyroclastic flow productivity and sustained dome collapse events are linked to pulses of high magma extrusion rates

calcium tschermak s pyroxene caalalsio6 from the allende and murray meteorites ebsd and micro raman characterizations calcium tschermak s pyroxene cats caalalsio 6 is well known as an important component in pyroxene it is a member of the ca clinopyroxene group in which al dominates in the m1 site pyroxenes with more than 80 mol cats were observed previously in ca al rich refractory inclusions cai from five carbonaceous chondrites this study re investigated the near end member cats in the allende and murray chondrites electron backscatter diffraction ebsd is used to establish that its crystal structure is monoclinic c2 c a 9 609 a b 8 652 a c 5 274 a 106 06 v 421 35 a 3 and z 4 its ebsd pattern is an excellent match to that of synthetic caalalsio 6 with the c2 c structure microraman is also carried out to confirm the crystal structure the allende cats with 46 00 wt al 2 o 3 and 97 mol al in the m1 site has the formula ca 1 02 al 0 97 fe 0 01 mg 0 01 0 99 si 1 00 al 1 00 2 00 o 6 it occurs as micrometer sized crystals along with melilite hibonite perovskite spinel corundum ti 3 rich pyroxene and grossular in a fluffy type a cai it is probably a secondary phase resulting from the alteration of gehlenitic melilite the cats in murray with a formula ca 0 98 al 0 81 mg 0 16 ti 0 04 4 1 01 si 1 11 al 0 89 2 00 o 6 occurs with hibonite and al rich diopside in a glass free refractory spherule this sample formed by solidification of a once molten droplet early in the history of the solar system

osl age and stratigraphy of the strauss sand sheet in new mexico usa abstract the strauss sand sheet occurs in south central new mexico usa and northern chihuahua mexico covering an area of about 4740 km2 its chronology is determined by 19 osl ages the sand sheet formed primarily during three phases of eolian deflation and deposition each phase with a separate sand source and under different climatic and environmental circumstances the first phase of eolian sedimentation occurred 45 to 15 ka with the deposition of unit 1 the sand source for the first phase was beach related features along the eastern shoreline of pluvial lake palomas in mexico the glacial age climate was cool wet and windy because of the southern path of the jet stream at that time after 15 ka with the onset of warmer conditions of the bolling allerod the shutting down of the palomas sand source and wet conditions of the younger dryas the sand sheet stabilized with weak soil development in unit 1 by 11 ka the climate shifted to holocene drying conditions and the second phase of sand accumulation began forming unit 2 the sand source was the local deflation of the previously deposited unit 1 sand the sand sheet stabilized again by 1 9 ka with slightly wetter late holocene climate a weak soil formed in unit 2 sand about a d 1500 and extending to about a d 1850 or later an a horizon formed on the sand sheet probably in response to a desert grassland vegetation during the period of wet climate of the little ice age in an anthropogenic third phase of eolian activity after a d 1850 the vegetation was likely disturbed by overgrazing and the unit 2 and a horizon unit 3 sands were deflated resulting in the deposition of a thin layer of massive eolian sand unit 4 across the sand sheet by about a d 1900 mesquite shrubs had increased in abundance and deflated sand largely from unit 2 began to accumulate around the shrubs forming coppice dunes unit 5 mesquite coppice dunes continued to increase in number and volume during the twentieth century and at present dominate most of the sand sheet this third phase of eolian deflation deposition is ongoing today

flow and deposition of pyroclastic granular flows a type example from the 1975 ngauruhoe eruption new zealand small volume pyroclastic density currents pdcs are generated frequently during explosive eruptions with little warning assessing their hazard requires a physical understanding of their transport and sedimentation processes which is best achieved by the testing of experimental and numerical models of geophysical mass flows against natural flows and or deposits to this end we report on one of the most detailed sedimentological studies ever carried out on a series of pristine small volume pdc deposits from the 1975 eruption of ngauruhoe volcano whose emplacement were also witnessed during eruption using high resolution gps surveys a series of lateral excavations across the deposits and bulk sedimentological analysis we constrained the geomorphology internal structure and texture of the deposits with respect to laterally varying modes of deposition deposition from these pdcs began only on slopes at or around the material s angle of repose c 30 in unconfined settings the granular pdcs are interpreted to have been quasi steady forming sheets and lobes around the angle of repose where flows were confined sheet like proximal facies made up around 10 of the deposit volume at the angle of repose but 90 of the material was deposited from apparently unsteady inertial granular pdcs as a distal levee and channel facies on slopes well below the repose angle hence confined pdcs were able to travel up to 50 farther than unconfined flows in the distal facies the deposit width is inversely correlated to the local slope and the height of the levees above the deposit centreline is positively correlated with slope internally the deposits comprise three parts a coarse grained fines free sole layer that laterally connects to levees zone i an ashy matrix supported central body zone ii and an overlying coarse plaster of clasts zone ii trends in grain size data suggests these zones derive from a continuous un mixing of coarse particles from the initial bulk material by granular segregation that preferentially drives large particles to the upper free surface of the flow where they are concentrated at the front of flow before being deposited and overrun by comparison to analogue experiments we suggest a model of flow and deposition where the temporally and spatially varying mode of deposition is determined by the flow velocity the local slope the vertical velocity gradient the velocity gradient at the free surface and the vertical deposition rate using this model estimated vertical deposition rates of c 5 cm s 1 from the ngauruhoe pdcs agree with those determined in laboratory experiments on inertial granular flows

evidence of active dune sand on the great plains in the 19th century from accounts of early explorers eolian sand is extensive over the great plains of north america but is at present mostly stabilized by vegetation accounts published by early explorers however indicate that at least parts of dune fields in nebraska colorado kansas new mexico and texas were active in the 19th century based on an index of dune mobility and a regional tree ring record the probable causes for these periods of greater eolian activity are droughts accompanied by higher temperatures which greatly lowered the precipitation to evapotranspiration ratio and diminished the cover of stabilizing vegetation in addition observations by several explorers and previous historical studies indicate that rivers upwind of great plains dune fields had shallow braided sandy channels as well as intermittent flow in the 19th century wide braided sandy rivers that were frequently dry would have increased sand supplies to active dune fields we conclude that dune fields in the great plains are extremely sensitive to climate change and that the potential for reactivation of stabilized dunes in the future is high with or without greenhouse warming

grain size segregation and levee formation in geophysical mass flows 1 data from large scale debris flow experiments are combined with modeling of particle size segregation to explain the formation of lateral levees enriched in coarse grains the experimental flows consisted of 10 m3 of water saturated sand and gravel which traveled 80 m down a steeply inclined flume before forming an elongated leveed deposit 10 m long on a nearly horizontal runout surface we measured the surface velocity field and observed the sequence of deposition by seeding tracers onto the flow surface and tracking them in video footage levees formed by progressive downslope accretion approximately 3 5 m behind the flow front which advanced steadily at 2 m s 1 during most of the runout segregation was measured by placing 600 coarse tracer pebbles on the bed which when entrained into the flow segregated upwards at 6 7 5 cm s 1 when excavated from the deposit these were distributed in a horseshoe shaped pattern that became increasingly elevated closer to the deposit termination although there was clear evidence for inverse grading during the flow transect sampling revealed that the resulting leveed deposit was strongly graded laterally with only weak vertical grading we construct an empirical three dimensional velocity field resembling the experimental observations and use this with a particle size segregation model to predict the segregation and transport of material through the flow we infer that coarse material segregates to the flow surface and is transported to the flow front by shear within the flow head coarse material is overridden then recirculates in spiral trajectories due to size segregation before being advected to the flow edges and deposited to form coarse particle enriched levees

estimation of porosity and water saturation in dual porosity pyroclastic deposits from joint analysis of compression shear and electromagnetic velocities in situ measurements of porosity and water saturation of pyroclastic deposits have the potential to improve interpretations of geology and hydrology in volcanic regions and provide more accurate estimates of dense rock equivalent for volcanic eruptions however rock property models must consider the dual porosity structure of pyroclastic deposits i e vesicles within pumices and intergranular pores vesicularity intergranular porosity and water saturation all affect the density elasticity and dielectric properties of pyroclastic materials which control seismic and electromagnetic velocities the data from active seismic and ground penetrating radar techniques may improve porosity and water saturation estimation if the responses of seismic and electromagnetic waves to porosity and water saturation variations are complementary in pyroclastic rocks we develop a dual porosity petrophysical model to calculate seismic and electromagnetic velocities of pumice with known intergranular porosity vesicul

origin of the late quaternary dune fields of northeastern colorado stabilized eolian deposits mostly parabolic dunes and sand sheets cover much of the landscape of northeastern colorado and adjacent parts of southwestern nebraska in four geographically distinct dune fields stratigraphic and soil geomorphic relations and accelerator radiocarbon dating indicate that at least three episodes of eolian sand movement occurred between 27 ka and 11 ka possibly between 11 ka and 4 ka and within the past 1 5 ka thus eolian sand deposition took place under both glacial and interglacial climatic conditions in the youngest episodes of eolian sand movement holocene parabolic dunes partially buried pleistocene sand sheet deposits late holocene sands in the fort morgan and wray dune fields to the south of the south platte river have trace element ratios that are indistinguishable from modern south platte river sands but different from ogallala formation bedrock which has previously been cited as the main source of dune sand on the great plains sands in the greeley dune field to the north of the south platte river have trace element concentrations that indicate a probable laramie formation source measurements of parabolic dunes indicate paleowinds from the northwest in all dune fields in good agreement with resultant drift directions calculated for nearby weather stations thus paleowinds were probably not significantly different from present day winds and are consistent with a south platte river source for the fort morgan and wray dune fields and a laramie formation source for the greeley dune field sand accumulated downwind of the south platte river to form the fort morgan duen field in addition sand was also transported farther downwind over the upland formed by the calcrete caprock of the ogallala formation and deposited in the lee of the upland on the southeast side because of high wind energy the upland itself served as a zone of sand transport but little or no sand accumulation took place on this surface these studies which demonstrate the importance of fluvial source sediments for dune fields in colorado may be applicable to other dune fields in north america because modern drift potentials in northeastern colorado are among the highest in the world the present stability of dunes in the region may be in part a function of the dunes being supply limited rather than solely transport limited extensive 7700 km2 late holocene dunes document that eolian sand in northeastern colorado is very sensitive to small changes in climate or fluvial source conditions

on pyroclastic flow emplacement in this note i investigate some theoretical characteristics of pyroclastic flow deposits assuming that these flows are bingham fluids probably the simplest non newtonian fluids pyroclastic flows are modeled as laminar debris flows moving on an inclined plane and their physics is discussed within the classical framework of lubrication theory using general hydrodynamics methods i show that the arrestment and emplacement of pyroclastic flows may be seen as the time asymptotic limit of their equations of motion this limit is found to be a nonlinear ordinary differential equation whose solution gives the shape of pyroclastic flow deposits the model suggests that these flows stop when the supply of material from the source is depleted deposit thickness is controlled principally by the flow yield stress z a parameter characteristic of bingham fluids while deposit length a measure of flow mobility depends on z on the source flux q0 and on the slope of the solid substrate even in this simple model theoretical analysis shows a complex correlation between flow parameters and deposit profiles

pyroclastic flow erosion and bulking processes comparing field based vs modeling results at tungurahua volcano ecuador pyroclastic density currents pdcs are high temperature and high velocity mixtures that threaten populations in the vicinity of many active volcanoes deciphering the cause of their remarkable mobility is essential for volcanic hazard analysis but remains difficult because of the complex processes occurring within the flows here we investigate the effect of bulking on dense pdc mobility by means of a double approach first we estimate the amount of material incorporated into scoria flows emplaced during the august 2006 eruption of tungurahua volcano ecuador for this we carry out a detailed analysis of 3d corrected digital images of well exposed scoria flow deposits componentry analysis indicates that pdc bulking occurs principally on the steep 25 upper slope of the volcano and the deposits typically comprise 40 50 wt of non juvenile i e accessory and accidental material secondly we develop a simple stress related grain by grain equation of erosion combined with two simple depth averaged geophysical mass flow models that compare the bulking mechanism to a non fluidized and a fluidized flow two behaviors based on coulomb and plastic rheologies are used to reproduce on a first order basis the 2006 tungurahua pdcs cross check comparisons between these modeled cases and the erosion pattern inferred from field based data allow us to evaluate the accuracy of our modeling assumptions regardless of the rheological regime the pdc induced erosion pattern of the 2006 tungurahua eruption can only be reproduced by fluctuations of the flow s basal shear stress during emplacement such variations are controlled by flow thinning thickening processes notably through the formation of a thick non erosive flow body that pushes a thin frictional erosive front during pdc emplacement the input volume of juvenile material as well as the thickness of the erodible layer available prior to the eruption are additional key parameters our work highlights complexities in pdc erosion and bulking processes that deserve further study in terms of hazard assessment our findings reveal that incorporation and bulking translate into increased flow mobility i e the augmented flow mass enhances both flow velocity and runout distance up to 20 these outcomes should be considered closely for hazard analysis at many other andesitic volcanoes worldwide where similar pdc events are common

relict nebkhas pimple mounds record prolonged late holocene drought in the forested region of south central united states the origin and significance of pimple mounds low elliptical to circular dune like features found across much of the south central united states have been debated for nearly two centuries we cored pimple mounds at four sites spanning the ozark plateau arkansas river valley and gulf of mexico coastal plain and found that these mounds have a regionally consistent textural asymmetry such that there is a significant excess of coarse grained sediment within their northwest flanks we interpret this asymmetry as evidence of an eolian depositional origin of these mounds and conclude they are relict nebkhas coppice dunes deposited during protracted middle to late holocene droughts these four mounds yield optically stimulated luminescence ages between 2400 and 700 yr that correlate with well documented periods of eolian activity and droughts on the southern great plains including the medieval climate anomaly we conclude vegetation loss during extended droughts led to local eolian deflation and pimple mound deposition these mounds reflect landscape response to multi decadal droughts for the south central u s the spatial extent of pimple mounds across this region further underscores the severity and duration of late holocene droughts which were significantly greater than historic droughts