modelling controls on aeolian dune field pattern evolution a second generation source to sink cellular automaton based model presented here captures and quantifies many of the factors controlling the evolution of aeolian dune field patterns by varying only a small number of parameters the role of sediment supply sediment availability and transport capacity together defined as sediment state in the development and evolution of an aeolian dune field pattern over long time scales is quantified from model simulations seven dune field patterns can be classified from simulation results varying the sediment supply and transport capacity that control the type and frequency of dune interactions the sediment availability of the system and ultimately the development of dune field patterns this model allows predictions to be made about the range of sediment supply and wind strengths required to produce the dune field patterns seen in the real world a new clustered dune field pattern is identified from model results and used to propose an alternative mechanism for the formation of superimposed dunes bedforms are hypothesized to cluster together simultaneously forming two spatial scales of bedforms without first developing a large basal dune with small superimposed dunes manipulation of boundary conditions produces evolving dune fields with different spatial configurations of sediment supply trends of spacing and crest length increase with decreasing variability as the dune field matures this simple model is a valuable tool which can be used to elucidate the dominant control of aeolian sediment state on the construction and evolution of aeolian dune field patterns

crustal modification during subduction zone magmatism evidence from the southern salar de uyuni region 20 22 s central andes late cenozoic volcanic rocks erupted in the southern salar de uyuni region of the central andes provide evidence for recent modification of both the lower and upper continental crust during subduction zone magmatism at a given sio 2 content k 2 o and related incompatible trace element concentrations increase eastward in basaltic andesite samples and are associated with increasing sr isotopic ratios and decreasing sr concentrations these data favor a model in which basaltic andesite magmas are contaminated by lower continental crust that becomes increasingly more mafic toward the active volcanic front because of relatively recent intrusion and hybridization by primary basaltic magmas compositions of andesitic lavas continue the geochemical trends established by the basaltic andesite samples except that sr isotopic ratios of lavas erupted at the arc front are constant to slightly decreasing with increasing sio 2 contents assimilation of upper crustal rocks that also vary in composition across the strike of the arc is the most plausible mechanism to produce the distinct sr isotopic trends of the andesitic lavas at the volcanic front the magmas producing the andesitic lavas assimilated rocks within the quaternary volcanic and plutonic complex of the andean arc itself toward the east the magmas assimilated basement rocks that become progressively older with distance from the volcanic front because of diminishing modification by late cenozoic arc magmatism thus the across arc geochemical trends in the southern salar de uyuni region are consequences of spatial variations in the composition of the lower and upper continental crust and these variations appear to be linked to the subduction process itself

provenance and transport process for interdune sands in the kumtagh sand sea northwest china abstract interdune areas are an important part of dune systems as they affect dune evolution and sand sea development however there has been little work on the provenance of interdune sediments our lack of knowledge of these sediments prevents a more complete understanding of sand sea formation and evolution in the present study we focused on the provenance of interdune sediments in the kumtagh sand sea based on their granular mineral and geochemical characteristics then further identified the spatial scope of the contribution of these sources to the interdune sediments and the associated transport mechanisms although sediment supply analysis suggested that the interdune sand may derive from the altyn tagh mountains beishan mountains and sanlongsha dune field the provenance signature based on the k rb and k ba ratios revealed that the ultimate sources were the altyn tagh mountains in the south and the beishan mountains in the north by plotting the identified provenance results on a map of the sand sea we found that the spatial scopes of contributions from these sources were separated at around 40 n however the existence of a fluvial load em1 and of reworked coarse particles em3 in the northern sand sea demonstrated that the interdune sands in this region were partly derived from the altyn tagh mountains in the south consequently by combining our results with the transport agents condition we concluded that the altyn tagh mountains supplied sediments to interdune areas by fluvial transport throughout the sand sea but that sediment in the northern sand sea was subsequently reworked and mixed with windblown sand originated from the beishan mountains

eolian dune interdune sand sheet and siliciclastic sabkha sediments of an offshore prograding sand sea dhahran area saudi arabia an offshore prograding sand sea exists along portions of the arabian gulf coastline near dhahran saudi arabia in this region sediments of eolian dune interdune sand sheet and siliciclastic sabkha intercalate with marine deposits this depositional setting is characterized by strong offshore winds which supply abundant sand to the coastline and cause at present time the outbuilding of the dune system this quartz detrital dominant setting contrasts markedly with the carbonate dominant setting resulting from onshore winds in the trucial coast area to the south the broad intercalation of eolian and marine deposits which results creates ideal potential for subregional stratigraphic petroleum traps due to pinch out of porous and permeable dune sands into impermeable m rine mudstones within the eolian system itself are potential reservoir rocks dunes sources organic rich sabkha and interdune deposits and seals zones of early cementation in all deposits early cementation is very common in all facies of the eolian sand sea the early cementation occurs owing to 1 soil formation 2 deposition of pore filling gypsiferous cements from saturated solutions near water table and 3 addition of sand size windblown evaporitic material to sands downwind of sabkhas

topographic correction for alos palsar interferometry l band synthetic aperture radar sar interferometry is very successful for mapping ground deformation in densely vegetated regions however due to its larger wavelength the capacity to detect slow deformation over a short period of time is limited stacking and small baseline subset sbas techniques are routinely used to produce time series of deformation and average deformation rates by reducing the contribution of topographic and atmospheric noise for large sets of images that are presently available from c band european remote sensing satellites ers 1 2 and environmental satellite envisat the standard stacking and sbas algorithms are accurate however the same algorithms are often inaccurate when used for processing of interferograms from l band advanced land observing satellite phased array type l band sar alos palsar this happens because only a limited number of interferograms is acquired and also because of large spatial baselines often correlated with the time of acquisition in this paper two techniques are suggested that can be used for removing the residual topographic component from stacking and sbas results thereby increasing their accuracy

the volcanic and magmatic evolution of volcan ollague a high k late quaternary stratovolcano in the andean central volcanic zone abstract volcan ollague is a high k calc alkaline composite volcano constructed upon extremely thick crust in the andean central volcanic zone volcanic activity commenced with the construction of an andesitic to dacitic composite cone composed of numerous lava flows and pyroclastic deposits of the vinta loma series and an overlying coalescing dome and coulee sequence of the chasca orkho series following cone construction the upper western flank of ollague collapsed toward the west leaving a collapse amphitheater about 3 5 km in diameter and a debris avalanche deposit on the lower western flank of the volcano the deposit is similar to the debris avalanche deposit produced during the may 18 1980 eruption of mount st helens u s a and was probably formed in a similar manner it presently covers an area of 100 km2 and extends 16 km from the summit subsequent to the collapse event the upper western flank was reformed via eruption of several small andesitic lava flows from vents located near the western summit and growth of an andesitic dome within the collapse amphitheater additional post collapse activity included construction of a dacitic dome and coulee of the la celosa series on the northwest flank field relations indicate that vents for the vinta loma and post collapse series were located at or near the summit of the cone the vinta loma series is characterized by an anhydrous two pyroxene assemblage vents for the la celosa and chasca orkho series are located on the flanks and strike n55 w radial to the volcano the pattern of flank eruptions coincides with the distribution in the abundance of amphibole and biotite as the main mafic phenocryst phases in the rocks a possible explanation for this coincidence is that an unexposed fracture or fault beneath the volcano served as a conduit for both magma ascent and groundwater circulation in addition to the lava flows at ollague magmas are also present as blobs of vesiculated basaltic andesite and mafic andesite that occur as inclusions in nearly all of the lavas all eruptive activity at ollague predates the last glacial episode 11 000 a b p because post collapse lava flows are overlain by moraine and are incised by glacial valleys present activity is restricted to emission of a persistent 100 m high fumarolic steam plume from a vent located within the summit andesite dome sr and nd isotope ratios for the basaltic andesite and mafic andesite inclusions and lavas suggest that they have assimilated large amounts of crust during crystal fractionation in contrast narrow ranges in 143nd 144nd and 87sr 86sr in the andesitic and dacitic lavas are enigmatic with respect to crustal contamination

multi spatial analysis of aeolian dune field patterns abstract aeolian dune fields are composed of different spatial scales of bedform patterns that respond to changes in environmental boundary conditions over a wide range of time scales this study examines how variations in spatial scales of dune and ripple patterns found within dune fields are used in environmental reconstructions on earth mars and titan within a single bedform type different spatial scales of bedforms emerge as a pattern evolves from an initial state into a well organized pattern such as with the transition from protodunes to dunes additionally different types of bedforms such as ripples coarse grained ripples and dunes coexist at different spatial scales within a dune field analysis of dune field patterns at the intersection of different scales and types of bedforms at different stages of development provides a more comprehensive record of sediment supply and wind regime than analysis of a single scale and type of bedform interpretations of environmental conditions from any scale of bedform however are limited to environmental signals associated with the response time of that bedform large scale dune field patterns integrate signals over long term climate cycles and reveal little about short term variations in wind or sediment supply wind ripples respond instantly to changing conditions but reveal little about longer term variations in wind or sediment supply recognizing the response time scales across different spatial scales of bedforms maximizes environmental interpretations from dune field patterns

sorting out abrasion in a gypsum dune field 1 grain size distributions in eolian settings are the result of both sorting and abrasion of grains by saltation the two are tightly coupled because mobility of particles determines abrasion rate while abrasion affects the mobility of particles by changing their mass and shape few field studies have examined this quantitatively we measured grain size and shape over a 9 km transect downwind of a line sediment source at white sands national monument a gypsum dune field the sediment source is composed of rodlike elongate coarse particles whose shapes appear to reflect the crystalline structure of gypsum dispersion in grain size decreases rapidly from the source coarse particles gradually become less elongate while an enrichment of smaller more elongate grains is observed along the transect transport calculations confirm that white sands is a threshold sand sea in which 1 the predominant particle diameter reflects grains transported in saltation under the dune forming wind velocity and 2 smaller elongate grains move in suspension under this dominant wind size selective transport explains first order trends in grain size however abrasion changes the shape of saltating grains and produces elongate smaller grains that are spallation and breaking products of larger particles both shape and size changes saturate 5 6 km downwind of the source as large particles become more equant abrasion rates slow down because protruding regions have been removed such asymptotic behavior of shape and abrasion rate has been observed in theory and experiment and is likely a generic result of the abrasion process in any environment

factors determining desert dune type while most observers recognize four elemental types of desert dunes longitudinal transverse barchan and star1 3 there is little agreement about which factors determine these types the angular relationships between the resultant of sand shifting winds and both the crest and principal slipfaces of the elemental types have been discussed qualitatively for many decades these relationships have been quantified but the wide range of dune types that combine the elemental forms and the juxtaposition of different dune types show that wind regime is not the only determinant for example sand availability has been considered important we have now quantified the importance of both wind regime and sand availability as determinants of dune type we show here that the four elemental types occur in areas uniquely defined by both the equivalent sand thickness of sediments held in the dunes and a measure of directional variability of sand moving winds wind strength does not appear to be important vegetation has an ambiguous role and the particle size of dune sediments is unimportant

estimation of arctic glacier motion with satellite l band sar data offset fields between pairs of jers 1 satellite sar data acquired in winter with 44 days time interval were employed for the estimation of arctic glacier motion over svalbard novaya zemlya and franz josef land the displacement maps show that the ice caps are divided into a number of clearly defined fast flowing units with displacement larger than about 6 m in 44 days i e 50 m year the estimated error of the jers 1 offset tracking derived displacement is on the order of 20 m year occasionally azimuth streaks related to auroral zone ionospheric disturbances were detected and dedicated processing steps were applied to minimize their influence on the estimated motion pattern our analysis demonstrated that offset tracking of l band sar images is a robust and direct estimation technique of glacier motion the method is particularly useful when differential sar interferometry is limited by loss of coherence i e for rapid and incoherent flow and large acquisition time intervals between the two sar images the jers 1 results obtained using sar data acquired by a satellite operated until 1998 raise expectations of l band sar data from the alos satellite launched in early 2006

monitoring muztagh kuksai glacier surface velocity with l band sar data in southwestern xinjiang china this study presents the results of measuring surface velocity fields of alpine glaciers with multi temporal alos palsar synthetic aperture radar sar data using the normalized cross correlation technique the main limitations of spaceborne optical data and interferometric sar for retrieving reliable interferometric product are firstly discussed next an efficient method of deriving surface velocity with spaceborne sar system using the intensity tracking method based on the cross correlation optimization is expounded this method is an invaluable alternative way of estimating the glacier surface field when the differential sar interferometry is limited by the loss of coherence and can also overcome the drawback of the lack of available optical data in alpine glacier areas the method was successfully applied in the region of the muztagh kuksai glacier using alos palsar l band data with 44 days temporal separation the glacier surface velocity fields were obtained for two different time intervals 14 january to 11 march 2009 and 1 september to 17 october 2009 the accuracy of the method was estimated from the residual value in the non glacier area which is often used to evaluate the performance of the approach for monitoring the glacier surface velocity finally the distribution maps of the surface velocity fields on the muztagh kuksai glacier were retrieved with an accuracy of 0 3 m sd 0 2 m using l band spaceborne sar data the results show that overall average velocity for 1 september to 17 october in 2009 is about 11 faster than that for 14 january to 11 march in 2009 it is concluded that the potential of monitoring the long term evolution of glaciers with sar data should be emphasized

application of image cross correlation to the measurement of glacier velocity using satellite image data abstract image to image cross correlation software is applied to pairs of digital satellite images to map the velocity field of moving ice this technique uses small scale glacial surface features such as crevasse scars and snow dunes as markers on the surface of the moving ice displacements of the surface features are mapped by selecting small image areas centered on distinct features or by dividing a large area of densely featured glacial surface into a grid of areas and searching a subsequent image for matching areas using a cross correlation algorithm interpolation of the peak correlation values allows the displacements to be measured to subpixel accuracy resulting in very precise velocity measurements cross correlation is also applied to provide image coregistration in areas devoid of bedrock exposures in such areas subtle large scale topographic undulations in the ice surface related to underlying bedrock structure may be correlated by using large image areas and low pass filtered images both types of applications are demonstrated using ice stream d and ice stream e in west antarctica as test areas a high resolution map of the velocity field of the central portion of ice stream e generated by the displacement measuring technique is presented the use of cross correlation software is a significant improvement over previous manually based photogrammetric methods for velocity measurement and is far more cost effective than in situ methods in remote polar areas

satellite radar interferometry for monitoring ice sheet motion application to an antarctic ice stream satellite radar interferometry sri provides a sensitive means of monitoring the flow velocities and grounding line positions of ice streams which are indicators of response of the ice sheets to climatic change or internal instability the detection limit is about 1 5 millimeters for vertical motions and about 4 millimeters for horizontal motions in the radar beam direction the grounding line detected by tidal motions where the ice goes afloat can be mapped at a resolution of 0 5 kilometer the sri velocities and grounding line of the rutford ice stream antarctica agree fairly well with earlier ground based data the combined use of sri and other satellite methods is expected to provide data that will enhance the understanding of ice stream mechanics and help make possible the prediction of ice sheet behavior

compilation of a glacier inventory for the western himalayas from satellite data methods challenges and results abstract due to their sensitive reaction to changes in climatic conditions glaciers have been selected as an essential climate variable ecv although a large amount of ice is located in the himalayas this region is yet only sparsely represented in global glacier databases accordingly a sound and comprehensive change assessment or determination of water resources was not yet possible in this study we present a new glacier inventory for the western himalayas compiled from landsat etm scenes acquired between 2000 and 2002 coherence images from alos palsar image pairs the srtm digital elevation model dem and the aster global dem gdem several specific challenges for glacier mapping were found in this region and addressed they are related to debris cover orographic clouds locally variable snow conditions and creeping permafrost features in cold dry regions additional to seven topographic parameters that are obtained from the aster gdem for each glacier we also determined the relative amount of debris cover on the glacier surface the inventory contains 11 400 glaciers larger than 0 02 km2 which cover a total area of 9 310 km2 analysis of the inventory data revealed characteristic patterns of mean glacier elevation and relative debris cover amounts that might be related to the governing climatic conditions the full dataset will be freely available in the glims glacier database to foster further analyses and modeling of the glaciers in this region

seismicity and shape of the subducted nazca plate an updated compilation of earthquake locations and focal mechanism solutions from the international seismological centre and preliminary determination of earthquakes is the basis of a comprehensive study of the geometry of the wadati benioff zone beneath western south america the new data support previous mapping of a sharp flexure rather than a tear in the subducted nazca plate beneath southern peru and provide evidence for a similar flexure in the southward transition from nearly horizontal subduction to a slab with 30 dip at latitude 33 s in contrast the transition from 30 slab dip beneath bolivia to a nearly horizontal dip in the region between 28 s 32 s is more gradual occurring over several hundred kilometers of along strike distance between 20 s and 32 s this southward flattening corresponds to a broadening of a horizontal benchlike part of the subducted plate formed between 100 and 125 km depth the transition in continental tectonic style near 27 s 28 s from a wide volcanically active plateau to a narrow nonvolcanic cordillera appears not to be associated with the main slab flattening which begins to the north of these latitudes but with a more abrupt change in curvature of the subducted slab from convex upward to concave upward immediately below the plate boundary interface the concept of gaussian curvature is applied to slab bending to explain how subduction geometry is affected by the shape of the south american plate we hypothesize that the polarity of vertical curvature in the subducting slab is governed by the orientation of lateral curvature of the plate margin focal mechanism solutions for intermediate and deep earthquakes are grouped by geographic region and inverted for the orientation and relative magnitudes of the principal stresses results of the inversion indicate that downdip extension dominates in the slab above 350 km while downdip compression dominates at greater depths

characterizing formation processes of rimrock lake a late pleistocene holocene playa harney basin south eastern oregon usa using an end member mixing analysis

cenozoic stratigraphy and basin tectonics of the andes mountains 20 28 south latitude clastic sedimentary basins have evolved during the past 40 m y in the central andes lat 20 28 s in response to shifting patterns of magmatism and deformation the distribution of these basins and their genetic relations to uplifted areas are analogous to the basins and mountain belts of the north american rocky mountains during the late cretaceous and early cenozoic petroleum exploration has focused on zones underlying the upper cenozoic strata along the eastern margin of the andes mountain belt between about 40 and 25 ma a nonmarine basin extended across the region that is now the andes mountains between about 25 and 10 ma the western part of the former basin became the site of a volcanic arc sediment accumulation continued in the east where marine intercalations demonstrate the low elevation of the basin after 10 ma the volcanic arc remained active and locally widened and crustal shortening caused regionally important thrust and reverse faulted ranges during the past 10 m y up to 4 000 m of coarse clastic debris accumulated in a foreland basin on the eastern flank of the mountains meanwhile in the interior of the mountains over 4 000 m of fine grained strata and evaporites accumulated in local depocenters

the holocene history of the white sands dune field and influences on eolian deflation and playa lakes abstract white sands national monument is the world s largest gypsum dune field the dunes are downwind of a 20 m deep 19 km wide deflation basin containing large playa lakes today the gypsum sand is derived from the edge of the deflation basin next to the dune field rather than the alkali flat and playa lakes where gypsum crystals are forming three erosional shorelines mark wetter episodes when playa lakes formed in the deflation basin successively younger shorelines formed within older ones as the basin deepened but was not widened by deflation the modern shoreline is forming around lake lucero playa the oldest shoreline termed l1 is degraded and formed near the pleistocene holocene transition deflation from the l1 to the l2 shoreline cut through pleistocene bedded evaporites and probably marks initiation of the dune field this event was before 5840 yr bp based on radiocarbon dates this reinforces an evolving consensus that episodes of deflation have characterized desert basins in the southwestern united states regional deflation events have been dated at 7000 and 4000 yr bp the shorelines imply the white sands dune field was created in short episodes and the modern dune field may not represent conditions during expansion of the dune sea

early landslide detection based on d insar technique at the wudongde hydropower reservoir differential interferometric synthetic aperture radar d insar is an effective technique for geological disaster prevention in this study an early landslide detection method based on the d insar technique is proposed first sar data are used to monitor landslide deformation in the wudongde hydropower reservoir then the ground surface deformation is derived by using the d insar technique which includes both soil and non soil deformations to remove the non soil deformation the vertical deformation filter method and slope deformation filter method for extracting soil deformations are established and the error of d insar results is analyzed by using two methods permanent scatterers insar and corner reflectors insar the errors caused by the atmospheric delay are estimated quantitatively additionally the relationship between the landslide deformation and the temporal spatial change of the sar data is analyzed and used to identify landslides finally through the proposed early landslide detection method the jinpingzi landslide in the wudongde area is investigated to validate the proposed method and the other unknown landslides in this area are also detected which demonstrates the feasibility of the proposed method the outcome of this study provides a workable technique for early detection of landslides in valley reservoir areas

intracrustal derivation of na rich andesitic and dacitic magmas an example from volcan ollague andean central volcanic zone andesitic and dacitic lavas erupted from quaternary stratovolcanoes in the central volcanic zone cvz of the andes have major and trace element compositions similar to proposed melts of subducted mid ocean ridge basalt and na rich trondjhemites tonalites and granodiorites ttg in early archean high grade gneiss terrains suites of lavas from individual volcanoes have average la yb of 25 45 sr y of 30 65 yb contents of 1 5 1 1 ppm and na 2 o contents 3 8 wt with lavas erupted on the volcanic front displaying the most affinity to the early archean suites because slab melting is not involved in the derivation of the cvz magmas these data indicate that rocks with early archean ttg compositions can also be produced through intracrustal differentiation processes isotopic major element and ree data from volcan ollague are consistent with a model incorporating contamination of mantle derived basaltic magmas in garnet bearing deep continental crust to produce basaltic andesite magma followed

the use of grain size distribution patterns to elucidate aeolian processes on a transverse dune of thar desert india the grain size distribution of aeolian dune sands in the thar desert india was analyzed and compared with three model distributions log normal log hyberbolic and log skew laplace to determine the best fit statistical model in total 51 samples were collected along a single transect over a transverse dune of which 15 were from the stoss side 12 from the crest and 24 from the lee side samples were collected during a calm period in the afternoon of a winter s day it was observed that of these 51 samples 33 fit best to a log hyperbolic distribution 14 fit best to a normal distribution and only four fit best to a laplace distribution however it was further observed that of 24 samples from the lee side 13 fit best to a normal distribution eight fit best to a hyperbolic distribution and three fit best to a laplace distribution of 12 samples from the crest of the dune 11 fit best to the log hyperbolic distribution only one to the laplace distribution but none to a normal distribution of 15 samples from the stoss side of the dune only one sample best fits a normal distribution 14 fit best to a log hyperbolic distribution and none best fit to a laplace distribution during sample collection a calm period prevailed and there was no dusty wind it was therefore assumed that in the initial stage a mixture of coarse medium and fine sands was laid down on the stoss side of the dune as wind speeds increased and saltation started the coarser fractions were segregated and lagged behind on the stoss slope in the final stage when the remaining intermediate and finer fractions reached the dune crest the finer fractions were winnowed away to suspension from the crest of the dune as a result a narrow range of intermediate sized sediments was deposited by rolling down the lee side to explain the development of log normality in such a situation both the coarser and finer fractions to which the skewed distributions can be attributed are separated from the initial mixture of coarse intermediate and fine fractions hence the main criteria for the development of a normal distribution is the lack of skewed fractions and the concentration of the narrow intermediate size fractions in the final grain size distribution this is also corroborated with the index of symmetry which is a measure of the difference between the angle of two slopes of the hyperbolic distribution as represented by the coarser and finer fractions copyright 2010 john wiley sons ltd

the distribution of carbonate eolianite abstract carbonate eolianite forms distinctive coastal landforms on many mid latitude continents and islands numerous studies of extensive continental and smaller island deposits in both hemispheres have shown the eolianites are predominantly pleistocene in age the coorong coastal plain of south australia contains the world s longest record of eolianite deposition revealing that major phases of carbonate accumulation occurred during interglacial and some interstadial sea level highstands throughout the quaternary similarly the well studied eolianite islands of bermuda and the bahamas record a close match between dune accretion and sea level highstands since the middle pleistocene several other eolianite deposits appear to have formed at least partially during glacial periods the glacial age deposits are eolian reworked relict shelf or coastal sediments or remnants of former highly mobile coastal dunes sourced from low sea level shorelines the distribution and bioclastic composition of large scale eolianite deposits suggests carbonate production on shallow shelves and banks is the ultimate control on the formation of eolianite the bulk of the carbonate comprising those eolianites is heterozoan being produced where there is low terrigenous sediment input in dominantly temperate cool water and subtropical carbonate provinces quaternary cyclical movements of sea level have also controlled the form and rate of coastal carbonate deposition with repeated pulses of sedimentation during highstands forming laterally coalesced vertically stacked or composite dune successions major unconformities within the deposits are marked by paleosols which record hiatuses in coastal sedimentation in several regions major eolianite units overlie coastal deposits of terrigenous sediment those successions suggest that the trend towards aridity and reduction in the supply of terrigenous sediment to shelves during the quaternary has enhanced the production of carbonate and the deposition of eolianite

surface motion of mountain glaciers derived from satellite optical imagery a complete and detailed map of the ice velocity field on mountain glaciers is obtained by cross correlating spot5 optical images this approach offers an alternative to sar interferometry because no present or planned radar satellite mission provides data with a temporal separation short enough to derive the displacements of glaciers the methodology presented in this study does not require ground control points gcps the key step is a precise relative orientation of the two images obtained by adjusting the stereo model of one slave image assuming that the other master image is well georeferenced it is performed with numerous precisely located homologous points extracted automatically the strong ablation occurring during summer time on the glaciers requires a correction to obtain unbiased displacements the accuracy of our measurement is assessed based on a comparison with nearly simultaneous differential gps surveys performed on two glaciers of the mont blanc area alps if the images have similar incidence angles and correlate well the accuracy is on the order of 0 5 m or 1 5 of the pixel size similar results are also obtained without gcps an acceleration event observed in early august for the mer de glace glacier is interpreted in term of an increase in basal sliding our methodology applied to spot5 images can potentially be used to derive the displacements of the earth s surface caused by landslides earthquakes and volcanoes

generation of sodium rich magmas from newly underplated basaltic crust sodium rich rocks of trondhjemite tonalite dacite ttd or granodiorite ttg suites form much of precambrian continental crust1 they are thought to have formed by partial melting of subducted oceanic crust2 3 a process that would have been much more widespread early in earth history than at present owing to the higher thermal gradients prevailing at that time4 phanerozoic ttd suites do exist however and seem also to relate to subduction zones5 defant and drummond6 proposed that these suites form where young 25 myr hot oceanic lithosphere is subducted and melts thus locally simulating the conditions that led to widespread crustal growth in the archaean here we describe plutonic and volcanic rocks from the cordillera blanca complex in peru which have characteristics of the high al ttd suite but which were produced above a subduction zone containing a 60 myr old slab we present evidence that the complex formed by partial melting of newly underplated basaltic crust and argue that this mechanism should be considered more generally as an additional way of generating sodium rich arc magmas

transport and mixing of eolian sand from local sources resulting in variations in grain size in a gypsum dune field white sands new mexico usa abstract the white sands dune field new mexico usa provides a unique opportunity to study sources and eolian transport of sand end member mixing analysis provides unbiased correlation of the grain size distributions of populations that mix sands from four different local source surface types textural differences between sources allow local transport paths to be deduced in total 1214 surface samples from 10 dunes and 2 downwind oriented transects were collected neither elevation on the dune lee or stoss location nor distance downwind correlated with mean grain size coarsest 10 d90 or sorting instead grain size distributions are controlled by mixing of locally sourced sand populations adjacent dunes can have different mean grain sizes resulting from different local source populations local within dune and between dune variability resulting from different sand sources dominates any larger scale trends across and within dunes four sand populations are identified based on microscopically observable differences in grain size shape and angularity each correlates with high loading of a different statistical factor derived from end member mixing analysis end member 1 em1 correlates with well sorted populations of finer grained equant rounded sands em2 correlates with samples that contain moderately sorted populations containing angular blades and crystal aggregates associated with erosional interdunes em3 is associated with samples of moderately to poorly sorted fine grained sand containing fine sand sized gypsum needles collected from areas of vegetated interdunes and em4 is associated with moderately well sorted coarse and very coarse grained sands collected from granule ripples these results suggest that downwind mixing of different populations and segregation by different depositional processes influence grain size distributions in the dune field rather than by dune scale or erg scale transport and sorting

grain size characteristics of dune sands in the central taklimakan sand sea abstract compared with the sand grain size of the other sand seas central taklimakan sand sea has some of the finest sands seen globally the dunes are composed of fine and very fine sands with a diameter between 2 00 and 4 00 0 25 0 063 mm there are differences in the grain size distributions for different dune types mean grain size of the compound complex crescent dune sands is 3 08 the compound dome dunes 3 21 the compound complex linear dune sands between 2 63 and 3 41 and the star dunes 2 81 from the northern edge of the sand sea towards southern edge the components of fine and very fine sands increase closely related to the wind regimes time scale for dune development and underlying sediments compared with the foregoing there are some differences for the compound complex linear dunes in the centre of taklimakan though the pattern of coarser crests does exist the sorting parameters indicate that the sands on the west flank of compound complex linear dunes are better sorted than that on the east flank and crest sampling on the superimposed dunes developed on the surface of the complex linear dunes suggests that the patterns of finer crest coarser crest all existed in central taklimakan under the conditions of low energy wind regime when fine sand is available the frequency of the pattern for finer crest and better sorting will increase sampling on the simple crescent dunes developed on the interdunes suggests that the simple dunes are developed originally with nearly the same grain size distributions and parameters with the development of the dunes and evolution of the dune morphology the grain size distributions of the dune sands varied under the actions of the wind regimes time scale and underlying sediments

barchan parabolic dune pattern transition from vegetation stability threshold 1 many dune fields exhibit a downwind transition from forward pointing barchan dunes to stabilized backward pointing parabolic dunes accompanied by an increase in vegetation a recent model predicts this pattern transition occurs when dune surface erosion deposition rates decrease below a threshold of half the vegetation growth rate we provide a direct test using a unique data set of repeat topographic surveys across white sands dune field and find strong quantitative support for the model threshold we also show the threshold hypothesis applied to a barchan dune results naturally in its curvature inversion as the point of threshold crossing progresses from the horns to the crest this simple general threshold framework can be an extremely useful tool for predicting the response of dune landscapes to changes in wind speed sediment supply or vegetation growth rate near the threshold a small environmental change could result in a drastic change in dune pattern and activity

variation in particle size distribution over a small dune the variation in particle size distribution for a sequence of sand samples collected from the surface of a small barchanoid dune along a sampling line parallel to the windflow is studied by means of the hyperbolic distribution the modal or typical value of the log size increases linearly with distance from the windward foot to the crest of the dune and falls off steeply on the lee side the spread of the log size distribution locally near the modal value is roughly constant on the windward side but decreases significantly down the slip face two other parameters of the four parameter hyperbolic distribution can be considered largely constant a comparison of the log size distributions for heavy and light mineral grains based on a selected set of the samples showed that heavy and light minerals follow different hyperbolic patterns however the difference in modal size of the distributions for the two types of minerals was virtually constant among the samples

pattern analysis of dune field parameters as a basic form of pattern analysis the parameters of dune spacing defect density crest orientation and crest length are measured from remote images and treated statistically for dunes at white sands in new mexico the algodones in california the agneitir in mauritania and the namib in namibia statistical populations are identified from frequency plots of dune spacing and crest length field scale calculations of defect density and rose diagrams of crest orientation single populations characterize simple dune fields white sands whereas multiple populations characterize compound complex dunes algodones namib and complex dune fields agneitir as time increases dune fields show an increase in dune spacing and crest length a decrease in defect density more tightly clustered crest orientation and a reduction in the variance associated with measurements of these parameters the results are consistent with models of dune fields as self organizing complex systems in which a characteristic pattern emerges as a function of constructional time because pattern evolution is a function of time it may be possible to use pattern analysis to augment current methods of age determination statistically defined populations can be used in geomorphic backstripping to unstack generations of simple patterns that give rise to complex patterns and to reconstruct each generation in terms of construction time and palaeo wind regime copyright 2006 john wiley sons ltd

early diagenesis of eolian dune and interdune sands at white sands new mexico abstract the degree of early diagenesis in eolian dune and interdune sands at white sands new mexico is largely a function of the relationship between sand location and the water table most active and vegetation stabilized dune sands are in the vadose zone whereas interdune sands are in the capillary fringe and phreatic zones crystallographically controlled dissolution of the framework gypsum grains results in elongate prismatic etch pits on sand grains from the capillary fringe and phreatic zones whereas dissolution of sand grains in the vadose zone is slight causing minute irregularities on grain surfaces vadose water percolating through the sand is manifest as meniscus layers consequently dune sands in the vadose zone are cemented mainly by meniscus shaped gypsum at grain contacts pendant cements formed on the lower margins of some sand grains cementation in the capillary fringe and the phreatic zone is more extensive than the vadose regardless of strata type typically well developed gypsum overgrowths form along the entire edge of a grain or may encompass the entire grain complex diagenetic histories are suggested by multiple overgrowths and several episodes of dissolution on single grains attesting to changing saturation levels with respect to gypsum in the shallow ground water these changes in saturation are possibly due to periods of dilution by meteoric recharge alternating with periods of concentration of ions and the formation of cement due to evaporation through the capillary fringe

modeling grain size variations of aeolian gypsum deposits at white sands new mexico using aviris imagery abstract visible and near infrared vnir through short wavelength infrared swir 0 4 2 5 m aviris data along with laboratory spectral measurements and analyses of field samples were used to characterize grain size variations in aeolian gypsum deposits across barchan transverse parabolic and barchan dunes at white sands new mexico usa all field samples contained a mineralogy of 100 gypsum in order to document grain size variations at white sands surficial gypsum samples were collected along three transects parallel to the prevailing downwind direction grain size analyses were carried out on the samples by sieving them into seven size fractions ranging from 45 to 621 m which were subjected to spectral measurements absorption band depths of the size fractions were determined after applying an automated continuum removal procedure to each spectrum then the relationship between absorption band depth and gypsum size fraction was established using a linear regression three software processing steps were carried out to measure the grain size variations of gypsum in the dune area using aviris data aviris mapping results field work and laboratory analysis all show that the interdune areas have lower absorption band depth values and consist of finer grained gypsum deposits in contrast the dune crest areas have higher absorption band depth values and consist of coarser grained gypsum deposits based on laboratory estimates a representative barchan transverse dune transect 1 has a mean grain size of 1 16 449 m the error bar results show that the error ranges from 50 to 50 m mean grain size for a representative parabolic dune transect 2 is 1 51 352 m and 1 52 347 m for a representative barchan dune transect 3 t test results confirm that there are differences in the grain size distributions between barchan and parabolic dunes and between interdune and dune crest areas the t test results also show that there are no significant differences between modeled and laboratory measured grain size values hyperspectral grain size modeling can help to determine dynamic processes shaping the formation of the dunes such as wind directions and the relative strengths of winds through time this has implications for studying such processes on other planetary landforms that have mineralogy with unique absorption bands in vnir swir hyperspectral data

spatial and temporal variations in the andean subduction zone a comprehensive global study of the process of subduction of oceanic lithosphere has made it evident that a major role is played by the age of the subducted lithosphere the age dependence of subduction is of special interest in an understanding of the late cenozoic history of the andean subduction zone many of the complexities of this zone result from the peculiar circumstance that the zone is in transition from an early stage of consumption of old lithosphere 70 ma producing deep earthquakes towards the latest stage of consumption of young lithosphere without deep earthquakes this transition has induced an evolutionary pattern with significant temporal variations notably changes in dip and length of the subducted slab moreover the various segments of the south american subduction zone are in different stages of this evolution in comparison with the other segments the northern chile segment is in the earliest stage and therefore shows a much closer resemblance to the classic deep subduction zones in the western pacific than do other parts of the south american zone a roughly n s symmetry in development is found around northern chile with the ecuadorian and southern chilean near 40 45 s segments representing the latest stage to a large extent the temporal and spatial variations in lithospheric age at the trench originate from the reorganization in plate configuration which started with the break up of the farallon plate into the cocos plate and the nazca plate at about 25 ma

partial melting of subducting oceanic crust the conditions under which partial melting of subducting oceanic crust occurs can be determined by combining a partial melting model for basaltic compositions with two dimensional thermal models of subduction zones for porosities of 1 containing h20 the amount of partial melt generated at the wet basaltic solidus is limited to 100 mpa can be maintained by rocks close to or above their melting temperatures in the absence of high shear stresses substantial melting of the oceanic crust will only occur during subduction of very young 5 ma oceanic lithosphere partial melting of hydrated basalt amphibolites derived from the mid ocean ridge has been proposed e g 1 3 as being responsible for the generation of certain recent high al andesitic to dacitic volcanic rocks adakites three of these volcanic suites mount st helens southern chile and panama occur in volcanic arcs where oceanic crust 25 ma is being subducted at rates of 1 3 cm yr and the calculated thermal regime is several hundreds of degrees hotter than more typical subduction zone environments however oceanic lithosphere is not currently being subducted beneath baja and new guinea where recent adakites are also present suggesting that some adakite magmas may form by water undersaturated partial melting of underplated mafic lower crust or previously subducted oceanic crust further experimental work on compositions representative of oceanic crust is required to define the depth of possible adakite source regions more accurately

improvement of satellite radar feature tracking for ice velocity derivation by spatial frequency filtering outlet glaciers of ice sheets are the primary means of transporting ice from the interior to the oceans and their flow velocity is one control that determines the mass balance of ice sheets estimates of ice velocities particularly for remote areas are commonly based on satellite remote sensing data as radar based systems emit energy at frequencies high enough to penetrate clouds they can record backscatter signals from surfaces throughout the year radar data which are collected with repeat pass spaceborne platforms are therefore good for extracting ice velocities using interferometry for slow moving ice and the cross correlation techniques for fast moving ice here we present an improvement on the cross correlation technique that enables independent quality checks and enhances the spatial extent of the derived velocity fields filtering of esa european remote sensing satellite scenes based on a butterworth high pass spatial frequency filter focuses the cross correlation technique on smaller movable surface features instead of large fixed features it also allows a nonregional culling based on the signal to noise ratio of the velocities with the effect of increasing the coverage of robust velocity estimates

analysis of linear dune sediment form relationships in the kalahari dune desert wilson s 1972a b hypothesis of grain size control of dune spacing is tested using data from linear dunes in the kalahari dune desert the results confirm wasson and hyde s 1983b rejection of the universal applicability of the theory though this does not discount relevance to other dune types factors pertaining to the rejection of the grain size theory in the kalahari are considered results also demonstrated that the height and spacing of linear dunes are related but only when values are grouped for blocks of dunes the gradient of the h s relationship differs between dunefields possibly because sand supply differences have an effect upon dune geometry

granule ripples in the kumtagh desert china morphology grain size and influencing factors granule ripples are found mainly in four regions of the kumtagh desert in china they are characterized by an asymmetrical shape with gentle lower slopes on both sides and abrupt crests the ripples tend to be oriented perpendicular to the prevailing winds except when they form near obstacles such as yardangs the wavelengths range between 0 31 m and 26 m and heights h range from 0 015 m to 1 m the relationship between wavelength and height can be described by a simple linear function and the mean ripple index h is about 20 4 for the study sites the sediments are poorly sorted with negative to very negative skewness at lee and stoss slopes and between ripple troughs which confirms the poured in and shadow appearance described by previous researchers the bimodal or trimodal distributions of grains with modes of 1 16 0 5 and 3 16 and the enrichment of coarse particles at the ripple surface with coarse granule contents ranging between 5 2 and 62 1 indicate that the underlying layer is the original sediment source and that the granule ripples resist erosional processes although the impact of saltating particles and consequently the creep and reptation of coarse grains are responsible for granule ripple initiation at a micro scale however the characteristics of local sediments wind regimes and topographical obstacles as well as the feedbacks among bedform and airflow more strongly affect the development and alignment of granule ripples at a macro scale

estimation of rock glacier surface deformation using sar interferometry data the detection and quantification of surface deformation of an active rock glacier using the differential synthetic aperture radar sar interferometry d insar technique is presented an average deformation rate of 6 mm 35 days in the radar line of ight was estimated for the summer of 1992 the maximum deformation rate 18 mm 35 days was identified at the upper part of the rock glacier whereas the deformation rate at the snout of the rock glacier was about 10 mm 35 days the spatial distribution of the surface deformation in the d insar displacement map is smooth and supports the idea that ice is the stress transferring medium in rock glaciers

glacier motion estimation using sar offset tracking procedures two image to image patch offset techniques for estimating feature motion between satellite synthetic aperture radar sar images are discussed intensity tracking based on patch intensity cross correlation optimization and coherence tracking based on patch coherence optimization are used to estimate the movement of glacier surfaces between two sar images in both slant range and azimuth direction the accuracy and application range of the two methods are examined in the case of the surge of monacobreen in northern svalbard between 1992 and 1996 offset tracking procedures of sar images are an alternative to differential sar interferometry for the estimation of glacier motion when differential sar interferometry is limited by loss of coherence i e in the case of rapid and incoherent flow and of large acquisition time intervals between the two sar images in addition an offset tracking procedure in the azimuth direction may be combined with differential sar interferometry in the slant range direction in order to retrieve a two dimensional displacement map when sar data of only one orbit configuration are available

groundwater salinity as a control on development of eolian landscape an example from the white sands of new mexico abstract the white sands of southern new mexico form the largest field of gypsum dunes in the world the juxtaposition of several different types of dunes within the field has long been recognized and has generally been attributed to changes in the rate of sand transport across the dune field however steven fryberger fryberger s g 2003 geology of white sands national monument web page www2 nature nps gov geology parks whsa recently hypothesized however that a primary control is groundwater salinity the white sands dune field is underlain by saline waters fryberger proposed that parabolic dunes could form in topographic highs that accumulated a lens of fresher water derived from precipitation water with lower salinity allowed vegetation to grow and stabilized the sand except for the active noses of the parabolic dunes this study is a test of that hypothesis a study transect was established across the boundary between parabolic and barchan dunes groundwater and soil at six sites were sampled during december 2004 and march may and june of 2005 two sites were established in the parabolic field two in the barchans and two in the transition zone between them groundwater was found to be three times more saline in the barchan area conductivity and chloride decreased across the transition zone a gps topographic survey revealed two abrupt topographic steps one at the boundary between the barchans and the transition zone and a second at the edge of the parabolic field a second larger topographic step was found outside the study area defining a higher parabolic dune field these data indicate that fryberger s 2003 hypothesis is correct and groundwater is controlling the dune field morphology the dune field did not begin to form until the mid holocene 6500 years ago a compilation of dates shows that the parabolic dune field has probably been stable for the last 3500 years in contrast the barchan area has been recently deflated and exposed 2000 year old sediment near the surface

geochemical variations in andean basaltic and silicic lavas from the villarrica lanin volcanic chain 39 5 s an evaluation of source heterogeneity fractional crystallization and crustal assimilation at 39 5 s in the southern volcanic zone of the andes three pleistocene recent stratovolcanoes villarrica quetrupillan and lanin form a trend perpendicular to the strike of the andes 275 to 325 km from the peru chile trench basalts from villarrica and lanin are geochemically distinct the latter have higher incompatible element abundances and la sm but lower ba la and alkali metal la ratios these differences are consistent with our previously proposed models involving a a west to east decrease in an alkali metal rich high ba la slab derived component which causes an across strike decrease in degree of melting or b a west to east increase in the contamination of subduction related magma by enriched subcontinental lithospheric mantle silicic and mafic lavas from the stratovolcanoes have overlapping sr nd and o isotopic ratios silicic lavas also have geochemical differences that parallel those of their associated basalts e g rhyolite from villarrica has lower la sm and incompatible element contents than high sio2 andesite from lanin at each volcano the most silicic lavas can be modelled by closed system fractional crystallization while andesites are best explained by magma mixing apparently crustal contamination was not an important process in deriving the evolved lavas basaltic flows from small scoria cones 20 35 km from villarrica volcano have high incompatible element contents and low ba la like lanin basalts but trend to higher k rb 356 855 and lower 87sr 86sr 0 70361 0 70400 than basalts from either stratovolcano however all basalts have similar nd pb and o isotope ratios the best explanation for the unique features of the cones is that the sources of svz magmas e g slab derived fluids or melts of the subcontinental lithospheric mantle have varying alkali metal and radiogenic sr contents these heterogeneities are not manifested in stratovolcano basalts because of extensive subcrustal pooling and mixing this model is preferable to one involving crustal contamination because it can account for variable sr isotope ratios and uniform nd and pb isotope ratios among the basalts and the divergence of the cones from across strike geochemical trends defined by the stratovolcanoes

white sands dune field new mexico age dune dynamics and recent accumulations abstract the white sands dune field situated within the tularosa basin in southern new mexico is thought to have been largely derived by a stepwise progressive deflation of pleistocene lake otero strata with the onset of regional aridity optically stimulated luminescence osl dating of samples from a core that penetrated the gypsum accumulation of the dune field confirm a time of origin at 7000 yr dune sediment is characterized as lagged influx from previously stored lake otero sediment and contemporaneous influx derived from subsequent playas sediment became available for aeolian transport and dune field construction because of a falling water table driven by the regional aridity the current dune field is primarily a wet aeolian system in which the behavior of the accumulation surface over time is a function of the water table although surface cementation by gypsum also imparts aspects of a stabilizing system dune crests are oriented borderline transverse to the annual transport resultant and a monitored dune and its cross strata show that transverse winds from the sw during the late winter and spring account for most of the crest normal migration but a significant along crest component of migration of dune sinuosity occurs with fall and winter winds from the nw and n that strike the crests obliquely trenches across three interdune areas show dune sets and interdune strata climbing at about 0 1 depth of interdune scour increases with interdune streamwise length which acts to enhance the probability of dune cross strata deflation during arid years but also increases the probability of interdune accumulation because the water table shows a net rise over time within the trenches dune sets show a bundling of foresets between reactivation surfaces interpreted as annual cycles that reveal lee face reworking by the oblique nw and n winds and slipface progradation fostered by transverse winds from the sw a progression from grainflow dominated to wind ripple dominated cross strata within a single set revealed in the longest trench is consistent with along crest migration of dune sinuosity interdune laminations show light dark couplets interpreted as annual varves reflecting dry wet portions of the year the number of laminations preserved in vertical sections across an interdune area shows that the record is incomplete and endorses the interpretation of periods of interdune deflation a calculation of the current accumulation rate as based upon the climbing strata within the trenches is significantly greater than the long term accumulation rate determined by osl dates taken from the core in addition to compaction and possible dissolution of gypsum as partial explanations the long term accumulation rate may reflect significant variation in the accumulation rate over time short term deflation of accumulations on a regular basis and or the presence of unconformities within the gypsum body

the nevados de payachata volcanic region 18 s 69 w n chile ii evidence for widespread crustal involvement in andean magmatism volcanism extending over 11 ma is represented in the rocks of the nevados de payachata region culminating in the formation of two large composite stratocones within the last 500 000 years chemically distinct mafic magmas are erupted at a number of parasitic centers these cannot be related to each other by crystal fractionation and do not appear to be direct parents for the differentiated suites of the composite cones two distinct trends are defined by the intermediate and evolved rocks a high lile large ion lithophile element tio2 and ce yb lineage among the youngest rocks including the two major stratocones and a more typical calc alkaline trend among the older 1 ma rock types within individual volcanic centers differentiation involves fractionation of plagioclase pyroxene and hornblende with biotite and k feldspar in the more evolved rock types isotopic compositions sr pb nd o vary little with differentiation from basaltic andesite to rhyolite or with age contamination during differentiation from basalt to rhyolite may occur but the most mafic rocks erupted in the region are already enriched in incompatible trace elements and therefore may be insensitive to the effects of interaction with the crust the majority of data are similar to baseline compositions cenozoic parental magmas from other parts of the central andes and may reflect a relatively homogeneous magma source or source mixture throughout this central volcanic zone cvz which is distinct from the southern and northern andes and from island arc volcanic rocks

internal boundary layer model for the evolution of desert dune fields dune fields often show abrupt changes in morphology over short distances but the mechanism driving the changes has been unclear physical modelling and airborne altimetry from white sands new mexico show that the development of an internal boundary layer is linked to the vegetation and hydrologic patterns observed there desert dunes often exhibit remarkable changes in their morphology over short distances for example sediment rich dunes can break up into smaller isolated features and then become stabilized by plants over distances of kilometres1 2 3 4 5 6 these pattern transitions often coincide with spatial variations in sediment supply1 3 5 transport rate6 7 hydrology8 and vegetation9 10 11 but these factors have not been linked mechanistically here we hypothesize that the abrupt increase in roughness at the upwind margins of dune fields triggers the development of an internal boundary layer12 13 14 15 16 17 18 that thickens downwind and causes a spatial decrease in the surface wind stress we demonstrate that this mechanism forces a downwind decline in sand flux at white sands new mexico using a combination of physical theory14 15 16 17 18 19 repeated airborne altimetry surveys and field observations the declining sand flux triggers an abrupt increase in vegetation density which in turn leads to changes in groundwater depth and salinity showing that aerodynamics sediment transport and ecohydrology are tightly interconnected in this landscape we conclude that despite the documented complex climatic and geologic history of white sands20 internal boundary layer theory explains many of the observed first order patterns of the dune field

aeolian beach ridges and their significance for climate and sea level concept and insight from the levant coast east mediterranean abstract relict beach ridges of aeolian origin and associated soils are often used for inferring relative sea level and climate with contrasting results most studies link the aeolian coastal deposits to regressive phases some to high sea level stands and a few to intermediate relative sea level positions we interpret the apparent contradictions as indicating the lack of an over arching concept and the inconsistent usage of sea level related terms in this paper we present an integrated morpho sedimentological concept for a microtidal mid latitudinal coast and review existing data from the levant east mediterranean coast to evaluate the concept and to eliminate nomenclatural confusion a coastal depositional environment in a semi arid environment consists of shallow marine aeolian and alluvial facies which together form an aeolian beach ridge complex as a package of strata which respond simultaneously to sea level change a transgressive complex forms through reworking or overstepping of the coastal foredune and a regressive complex forms by downstepping under transgression the aeolian beach ridge represents the highstand deposit and its adjacent shallow marine sediment is the transgressive deposit under regression the complex represents the falling stage and the associated downdip surface marks the lowstand on the levant coast we find chronologically well constrained offlapping aeolian beach ridges as parts of six downstepping beach ridge complexes formed between 200 ka and 10 ka the complexes represent the falling stage systems tract fsst of a short lived 5th order depositional sequence when the shoreline shifted from a position close to the modern coastline to the shelf or below the shelf edge three of these fssts and their up dip and down dip super bounding surface together form the 4th order 100 ka sequence of the last interglacial glacial cycle the absence of transgressive highstand and lowstand systems tract is explained by the poor preservation potential due to the small sediment budget of the complex the falling stage complex has a high preservation potential because sediment source area increases while the sand drift potential remains above the local threshold on the levant coast sand delivery to the backshore continued during relative sea level falls for distances of up to 10 km between dune and coastline which is unprecedented in most modern analogues the significance of the dune soil succession for climate is limited because the dunes are governed by relative sea level change the vegetation response to changes in precipitation is non linear and the dune dynamics are characterised by low resilience and hysteresis

grain size variation on dunes in the southwest kalahari southern africa abstract grain size parameters mean standard deviation skewness and kurtosis were determined for 83 sediment samples from six dune cross profiles and one 28 km long profile on dunes in the southwest kalahari desert in southern africa although some studies elsewhere and previous studies in the kalahari have reported significant grain size variation over dune cross profiles data presented here show no systematic variation of grain size parameters except that sediments from the crest of a dune are almost invariably better sorted indicated by the standard deviation of the sample than samples from the base or plinth of the dune the proportion of fines 63 m in plinth sediments is also greater than in crest samples there is no significant trend in grain size parameters along the length of a linear dune this lack of significant pattern corresponds with similar findings for central australian dunes

an end member algorithm for deciphering modern detrital processes from lake sediments of lake donggi cona ne tibetan plateau china abstract deciphering significant sedimentological processes from a set of sediment samples is an important step in reconstructing environmental changes one approach going beyond classical methods is the unmixing of grain size distributions this paper presents a flexible end member modelling algorithm that is based on eigenspace analysis and considers inherent uncertainties it has been applied to the detrital grain size components of lacustrine surface sediment samples of lake donggi cona qinghai province china it allows up to five grain size end members to be characterised and quantified in an optimal model an end member with a major mode in the clay domain accounts for 34 of variance within the grain size data set it may represent sedimentation of suspension load from linear and laminar runoff during heavy precipitation events in summer three end members in the fine sand to medium silt domains make up 60 of lacustrine sedimentation they may represent local to remote aeolian processes that peak in wintertime a multimodal end member explaining the remaining 6 of variance may represent further fluvial and littoral dynamics or random fluctuations and measurement errors several model runs of different scaling and numbers of end members provided a suitable way to determine uncertainties inherent to the model a comparison of 12 different model runs and their respective uncertainties yielded a distinct model of robust end members the clay and medium silt end members are robust features of detrital sedimentation within lake donggi cona they alone explain 54 4 of total variance in the data however no spatial pattern or relation to water depth is found for any of the grain size end members thus when past detrital sedimentation at lake donggi cona is reconstructed a special focus should be on the robust features attributed to aeolian and suspension related sedimentation processes as well as on effective sediment mixing processes impeding a distinct correlation between grain size and spatial attributes further applications of the end member modelling algorithm to other depositional environments are encouraged to demonstrate its universal applicability

methodology for reconstructing wind direction wind speed and duration of wind events from aeolian cross strata 1 a methodology for reconstructing wind direction speed and event duration from aeolian dune cross strata was developed from analysis of crescentic dunes at white sands new mexico during wind events dune lee faces were surveyed lee face deposits mapped deposition rates measured grain size sampled by stratification type and winds characterized from meteorological and field data the spatial distribution of lee face stratification styles is a function of the incidence angle formed between the wind and the brinkline with secondary controls by wind speed and dune sinuosity and height sets of wind ripple strata form at incidence angles of 25 40 grainfall grainflow foresets over wind ripple bottomsets at 40 70 and grainflow grainfall foresets at 70 90 erosional reactivation surfaces form at incidence angles up to 15 bypass surfaces up to 25 the total sediment load is fractionated within lee face stratification types wind speed can be reconstructed from relationships between grain size transport mode shear velocity and grain settling velocity where the full range of grain transport modes occurs and grain size is limited by shear stress the shear velocity and grain size range in each transport mode can be estimated by assuming the coarse fraction in grainflow strata traveled in creep and the coarse fraction in grainfall traveled in saltation the minimum duration of a wind event can be estimated using measures of shear velocity dune height and dune forward migration method limitations arise with source area control on grain size extremes in wind events and severe truncation of sets of cross strata

growth of the continental crust a planetary mantle perspective abstract this paper addresses the net growth through time of the total continental crust cc not to be confused with sporadic growth of individual continental masses e g by accretion of island arcs a process that does not necessarily require net growth geochemists tend to emphasize differences between cc and oceanic crust oc but from a whole planet perspective cc and oc are remarkably similar in composition and density the cc oc distinction is canonically defined in terms of elevation however the earth s bimodal elevation pattern clearly reflects a genetic distinction the oc participates directly in mantle convection whereas the cc is the remaining relatively stable portion of the crust the earth s advective cooling mechanism requires massive subduction of lithosphere which due to the inherent buoyancy of crust tends to require a low crust total lithosphere thickness ratio given relatively constant lithosphere thickness except near thermally buoyant mid ocean ridges the earth responds by heaping most of its crust into a few thick continents allowing subduction to freely operate over a large area of relatively thin crust this crustal thickness bimodality engenders the bimodal elevation pattern prevailing wisdom tends to hold that the rate of cc growth has been slow and ongoing typical models show cc volume roughly proportional to 1 h where h is the total heat generation by the earth s k th and u however such models are generally vague as to the mechanism that supposedly holds back growth even after 4 5 ga the strong t dependence of mantle rheology probably ensured that the mantle took only a few million years to cool within a few hundred degrees of its modern t gradual compositional evolution of the cc from a plausible initial composition e g basaltic anorthositic might have slightly lowered the mean cc density but this effect is of second order importance in comparison to the general increase in crust total lithosphere thickness ratio for any given crustal thickness engendered by temporal cooling of the mantle intense cratering occurring coevally with early intense crust mantle recycling probably reconstituted virtually all of the cc extant prior to 3 9 ga but cc was probably not recycled into the mantle any faster than it was regenerated lunar samples and meteorites provide strong circumstantial evidence that in primordial times the outer few hundred kilometers of all terrestrial planets were largely molten outcomes of primordial magmatism must have been strongly dependent on the pressure regimes within the planetary interiors in general the far greater dt dp of silicate melting curves vs adiabats probably tended to foster a layered magmasphere with a partially molten or paracumulate layer constrained by dt dp relationships to a p range of roughly 3 gpa surmounted by fully molten magma ocean layer also limited in thickness by efficient convective cooling in the earth p stabilized garnet and al rich pyroxene were key factors limiting ultimate yield of crustal feldspar this effect has been examined with quantitative models of high p fractional crystallization including in some models periodic replenishment of the magma ocean from below results indicate that a plausibly deep 300 400 km magma ocean would produce a crust comparable in both composition and thickness to that of the modern earth mildly worrisome discrepancies involve cao for which high p pyroxene compositions are poorly constrained and sio 2 the crust probably evolved to its present sio 2 rich composition through differentiation catalyzed by h 2 o which presumably was not as abundant in the magma ocean as in the crust soon afterward nominal model results for mean crustal thickness are typically 1 2 1 3 the modern global mean but for this parameter the model is designed to give conservatively high results so the discrepancy is probably not significant after the chaotic first few million years of solar system history i suggest that planetary size and composition for more than time govern crustal volume

mount st helens potential example of the partial melting of the subducted lithosphere in a volcanic arc mount st helens 50 km to the west of mount adams and the main cascade volcanic chain is only 80 km above the subducting oceanic lithosphere the elevated temperatures off the subducting slab because of the close proximity of the juan de fuca ridge to the trench may induce slab melting at a depth of 80 km dacites from mount st helens have geochemical compositions off magmas that are derived by direct partial melting of metamorphosed basalts at high pressure i e relatively high ai al2o3 15 at 70 sio2 low y and yb because of garnet and amphibole stability in the source low sc and high sr and eu trace element modeling of the partial melting of mid oceanic ridge basalt morb from the juan de fuca ridge that yields a hornblende eclogite residue can reproduce the mount st helens data results off the model are quite distinct from data derived from the mount adams volcanic rocks in contrast mount adams is 135 km above the subducting slab and is associated with normal arc magmatism believed to be derived from the mantle above the subducting plate the cascade are has been active in its present locality because of oblique subduction for the past 7 m y the major volcanoes along the arc have existed for at least 500 ka but mount st helens has existed for 40 ka we suggest that the subducting plate may have reached elevated temperatures because of the approach of north america to the juan de fuca ridge at 40 ka which initiated melting of the slab

spatial grain size sorting in eolian ripples and estimation of wind conditions on planetary surfaces application to meridiani planum mars the landscape seen by the mars exploration rover mer opportunity at meridiani planum is dominated by eolian wind blown ripples with concentrated surface lags of hematitic spherules and fragments these ripples exhibit profound spatial grain size sorting with well sorted coarse grained crests and poorly sorted generally finer grained troughs these ripples were the most common bed form encountered by opportunity in its traverse from eagle crater to endurance crater field measurements from white sands national monument new mexico show that such coarse grained ripples form by the different transport modes of coarse and fine grain fractions on the basis of our field study and simple theoretical and experimental considerations we show how surface deposits of coarse grained ripples can be used to place tight constraints on formative wind conditions on planetary surfaces activation of meridiani planum coarse grained ripples requires a wind velocity of 70 m s at a reference elevation of 1 m above the bed from images by the mars orbiter camera moc of reversing dust streaks we estimate that modern surface winds reach a velocity of at least 40 m s and hence may occasionally activate these ripples the presence of hematite at meridiani planum is ultimately related to formation of concretions during aqueous diagenesis in groundwater environments however the eolian concentration of these durable particles may have led to the recognition from orbit of this environmentally significant landing site

dune deformation in a multi directional wind regime white sands dune field new mexico as with most dune fields the white sands dune field in new mexico forms in a wind regime that is not unimodal in this study crescentic dune shape change deformation with migration at white sands was explored in a time series of five lidar derived digital elevation models dems and compared to a record of wind direction and speed during the same period for the study period of june 2007 to june 2010 244 sand transporting wind events occurred and define a dominant wind mode from the sw and lesser modes from the nnw and sse based upon difference maps and tracing of dune brinklines overall dune behavior consists of crest normal migration to the ne but also along crest migration of dune sinuosity and stoss superimposed dunes to the se the sw winds are transverse to dune orientations and cause most forward migration the nnw winds cause along crest migration of dune sinuosity and stoss bedforms as well as se migration of ne trending dune terminations the sse winds cause ephemeral dune deformation especially crestal slipface reversals the dunes deform with migration because of differences in dune segment size and differences in the lee face deposition rate as a function of the incidence angle between the wind direction and the local brinkline orientation each wind event deforms dune shape this new shape then serves as the boundary condition for the next wind event shared incidence angle control on dune deformation and lee face stratification types allows for an idealized model for white sands dunes copyright 2015 john wiley sons ltd

field evidence for surface wave induced instability of sand dunes barchans are crescent shaped dunes that move faster over desert surfaces than most other dune types a three year field study shows how they do it collisions and changes in wind direction destabilize the dunes generating surface waves that form new smaller barchans this prevents the formation of a single giant dune so plays a fundamental role in the development of dune patterns field studies of barchans crescent shaped dunes that propagate over solid ground under conditions of unidirectional wind1 have long focused on the investigation of an equilibrium between sand transport by wind and the control of air flow by dune topography2 3 4 which are thought to control dune morphology and kinematics5 6 7 because of the long timescale involved however the underlying dynamic processes responsible for the evolution of dune fields remain poorly understood8 here we combine data from a three year field study in the moroccan sahara with a model study to show that barchans are fundamentally unstable and do not necessarily behave like stable solitary waves as suggested previously9 10 11 12 we find that dune collisions and changes in wind direction destabilize the dunes and generate surface waves on the barchans because the resulting surface waves propagate at a higher speed than the dunes themselves they can produce a series of new barchans of elementary size by breaking the horns of large dunes the creation of these new dunes provides a mechanism for sand loss that prevents dune fields from merging into a single giant dune and therefore plays a fundamental role in the control of size selection and the development of dune patterns

alpine glacial topography and the rate of rock column uplift a global perspective abstract the present study investigates the influence of alpine glacial erosion on the morphology and relief distribution of mountain regions associated with varying rock column uplift rates we take a global approach and analyse the surface area distribution of all mountain regions affected by glacial erosion between latitudes 60 s and 60 n most surface area in glaciated mountain ranges is concentrated below the modern snowline as predicted by the glacial buzzsaw hypothesis above the modern snowline the analysed mountain regions all exhibit an exponential decay of surface area with height on the basis of this decay the analysed mountain regions fall within three distinct groups primarily reflecting variations in average values of rock column uplift rates mountain ranges affected by rapid rock column uplift display high above snowline relief and large decay lengths whereas inactive orogens have little relief above the modern snowline we find a surprisingly simple relation between hypsometry above the local snowline and regional tectonic activity