regional scale flows in mountainous terrain part i a numerical and observational comparison abstract this study uses observed data and a numerical simulation to examine the generation of thermally driven flows across the colorado mountain barrier on meso to meso scales the observations were collected from remote surface observing systems at exposed mountaintop locations throughout the state of colorado over the summers of 1984 88 as part of the rocky mountain peaks experiment rompex the data show the development of a recurrent circulation system across the colorado mountain barrier operating on a diurnal timescale from the observations the basic structure of the flow system appears as a daytime inflow toward the highest terrain and a nocturnal outflow away from it however when examined in detail the flow system exhibits more unusual behavior especially west of the barrier crest here winds in the early evening are occasionally observed to onset abruptly from an easterly direction generally counter to the upper level winds observations from rompex for 26 august 1985 are used

pore properties as indicators of breakdown mechanisms in experimentally weathered limestones the results are reported of four experimental weathering tests freeze thaw wetting and drying slake durability and salt weathering on five different types of limestone effective porosity mercury intrusion porosimetry and scanning electron microscopy were used to evaluate changes in pore properties while weight loss and fracture density were used to assess deterioration severity a primary aim was to observe modifications in porosity due to weathering and to draw inferences about the internal rock deterioration mechanisms taking place it is concluded that the five limestones not only show a wide range of resistance to weathering in general but considerable difference in resistance to particular weathering processes consequently when assessing durability it is essential to consider rock properties in the context of the weathering process to which the rock is subject the type of deterioration indicator used is also important in interpretation of durability a variety of pore modification mechanisms operate including changes in pore connectivity pore infilling and the introduction of additional void space there are indications that changes to the internal pore structure of rocks due to weathering may be a precursor to more substantial macrodeterioration copyright 2001 john wiley sons ltd

changing climate changing process implications for salt transportation and weathering within building sandstones in the uk salt weathering is a crucial process that brings about a change in stone from the scale of landscapes to stone outcrops and natural building stone facades it is acknowledged that salt weathering is controlled by fluctuations in temperature and moisture where repeated oscillations in these parameters can cause re crystallisation hydration de hydration of salts bringing about stone surface loss in the form of for example granular disaggregation scaling and multiple flaking however this traditional view of how salt weathering proceeds may need to be re evaluated in the light of current and future climatic trends indeed there is considerable scope for the investigation of consequences of climate change on geomorphological processes in general building on contemporary research on the deep wetting of natural building stones it is proposed that as stone may be wetter for longer ion diffusion may become a more prominent mechanism for the mixing of molecular constituents and a shift in focus from physical damage to chemical change is suggested data from ion diffusion cell experiments are presented for three different sandstone types demonstrating that salts may diffuse through porous stone relatively rapidly in comparison to for example dense concrete pore water from stones undergoing diffusion experiments was extracted and analysed factors controlling ion diffusion relating to time of wetness within stones are discussed continued saturation connectivity of pores mineralogy behaviour of salts sedimentary structure and potential changes in system dynamics as a result of climate change are addressed system inputs may change in terms of increased moisture input translating into a greater depth of wetting front salts are likely to be stored differently in stones with salt being in solution for longer periods during prolonged winter wetness this has myriad implications in terms of the movement of ions by diffusion and the potential for chemical change in the stone especially in more mobile constituents leading to a weakening of the stone matrix grain boundary cementing the output may be mobilisation and precipitation of elements leading to for example uneven cementing in the stone this reduced strength of the stone or compromised ability of the stone to absorb stress is likely to make crystallisation a more efficacious mechanism of decay when it does occur thus a delay in the onset of crystallisation while stonework is wet does not preclude exaggerated or accelerated material loss when it finally happens

salt weathering simulations under hot desert conditions agents of enlightenment or perpetuators of preconceptions because of access difficulties and inhospitable environmental conditions our understanding of rock weathering in hot deserts has been strongly influenced by laboratory simulations however a risk exists that results may come to owe more to experimental design than to actual environmental conditions experienced at the atmosphere rock surface interface this was especially true in early salt weathering simulations that seemingly sought to reinforce the orthodoxy of a physically dominated weathering environment driven by extremely high absolute temperatures and large diurnal temperature ranges however improvements in environmental sensors over the last 20 years have established the complexity of desert climates and the importance of microclimatic controls and allowed considerable refinement of experimental design this overview evaluates the implications of recent simulation studies and presents new information on possible fatigue effects of differential thermal expansion of salts and the salt weathering of test blocks under compressive loading in doing so it demonstrates how physical rock properties change during experimentation the importance of short term surface temperature fluctuations distinctions between the weathering of unconfined debris and larger rock surfaces the importance of moisture and salt applications that replicate their availability in deserts the importance of rock thermal properties in controlling their weathering response in environments dominated by radiative heating and cooling and the overall complexity of weathering regimes

rock warming and drying under simulated intertidal conditions part ii weathering and biological influences on evaporative cooling and near surface micro climatic conditions as an example of biogeomorphic ecosystem engineering the way in which rocks and engineering materials heat up and dry out in the intertidal zone is of relevance to both weathering and ecology these behaviours can be measured in the laboratory under controlled conditions designed to replicate those occurring in the field previous studies have demonstrated differences in thermal behaviours between rock types and through time as a result of soiling in terrestrial environments but the influence of weathering and colonization on rock behaviours in the intertidal zone has not been previously assessed we measured the warming and drying of blocks of rock limestone and granite and marine concrete during low tide events simulated in the laboratory before and after a period of exposure eight months on rock platforms in cornwall uk as well as differences between the material types temperatures of control unexposed and field exposed blocks differed in the order of 1 to 2 c drying behaviours were also different after field exposure differences during the first few hours of exposure to air and heat were attributed to discolouration and albedo effects over longer periods of time changes in the availability of near surface pore water as a result of micro scale bioerosion of limestone and the development of bio chemical crusts on marine concrete observed using scanning electron microscopy sem are suggested as mechanisms enhancing and reducing respectively the efficiency of evaporative cooling the retention of moisture by epilithic biofilms may also influence thermal and drying behaviours of granite these observations represent one of the first examples of cross scalar biogeomorphic linkages in the intertidal zone the significance of the results for the subsequent efficiency of weathering and near surface micro climatic conditions experienced by colonizing organisms is discussed the involvement of microorganisms in the creation of more or less ecologically stressful conditions through the alteration of substratum geomorphic properties and behaviours is suggested as an example of biogeomorphic ecosystem engineering copyright 2011 john wiley sons ltd

geostatistical analysis in weathering studies case study for stanton moor building sandstone geostatistical techniques for spatial prediction and spatial simulation have been used in an innovative application to the study of weathering of natural building stone the study investigates the differences in the spatial variation of permeability characteristics between fine and coarse grained stanton moor building sandstone non destructive permeability measurements using an unsteady state portable probe permeameter were made on three adjacent faces of two cubic blocks representative of fine to medium grained and medium to coarse grained stanton moor sandstone the findings provide greater understanding in the investigation of the durability characteristics of the stanton moor sandstone and show that the spatial distribution and variability of permeability is more important in predicting the overall strength and weathering properties than mean permeability and absolute minimum and maximum values the results suggest that both primary textural characteristics such as grain size and extent of cementation appear to be important factors in determining the overall durability properties of stanton moor sandstone as a building stone geostatistical analysis has been shown to be an important tool in the characterization of spatial variation for the investigation of weathering of building stones copyright 2006 john wiley sons ltd

comparisons of the circulation anomalies associated with extreme heat in different regions of eastern china abstractthe circulation associated with extreme heat eh typically shows an anomalous anticyclone that enhances temperature through adiabatic heating but this study indicates obvious spatial variation in eastern china the eh related circulation pattern in eastern china can be classified into three categories typical extratropical pattern monsoonal pattern and foehn pattern eh over northeastern china and eastern north china is characterized by a typical pattern involving an anomalous anticyclone and subsidence and the air temperature increases throughout almost the entire troposphere in contrast eh over the yangtze river valley and south china is associated with the monsoonal pattern over these regions the air temperature only increases in the lower troposphere as a result of anomalous subsidence and lower humidity that has resulted from a farther north transportation of water vapor by a stronger monsoonal southwesterly meanwhile the air temperature decreases in the upper troposphere because

diurnal circulation of the bolivian altiplano part ii theoretical and model investigations abstract the first step in the evolution of the diurnal circulation of grand plateaus is the matutinal buildup of inflow through mountain passes connecting the lowlands with the plateau proper maximum inward transport is attained in the afternoon corresponding observations at the bolivian altiplano are described in the first part of this paper here both a linear model and the fifth generation pennsylvania state university ncar mesoscale model mm5 are used to better understand the dynamics of this process first discussed is the solution to the linear sea breeze problem where a heated fluid layer is restricted to the half plane x 0 rapidly moving barotropic modes lead to surface pressure fall in the heated half plane and to pressure rise for x 0 slow baroclinic modes describe the horizontally expanding inflow toward the heated layer near the ground with return flow aloft this basic structure of the response carries over to more complicated topographies where a heated plateau with vertical side

observations of flow and turbulence in the nocturnal boundary layer over a slope measurements were conducted on an eastern slope of the salt lake basin slb as a part of the vertical transport and mixing experiment vtmx conducted in october 2000 of interest was the nocturnal boundary layer on a slope in particular katabatic flows in the absence of significant synoptic influence extensive measurements of mean flow turbulence temperature and solar radiation were made from which circulation patterns on the slope and the nature of stratified turbulence in katabatic winds were inferred the results show that near the surface 25 50 m the nocturnal flow is highly stratified and directed downslope but at higher levels winds strongly vary in magnitude and direction with height and time implying the domination of upper levels by air intrusions these intrusions may peel off from different slopes surrounding the slb have different densities and flow at their equilibrium density levels the turbulence was generally weak and continuous but sudden increases of turbulence levels were detected as the mean gradient richardson number dropped to rig about unity with a short timescale fluctuated on the order of a few tens of seconds while modulating with rig a longer along slope internal waves sloshing timescale of about half an hour the mixing efficiency or the flux richardson number of the flow was found to be a strong function of similar to that found in laboratory rig experiments with inhomogeneous stratified shear flows the eddy diffusivities of momentum and heat were evaluated and they showed a systematic variation with when scaled with the shear length scale and the rms rig vertical velocity of turbulence

cavernous weathering dynamical instability and self organization cavernous weathering may be conceptualized as a self reinforcing process characterized by positive feedback within the weathering system a morphometric study of caverns in the valley of fire state park nevada usa demonstrates the applicability of a dynamically unstable or conditionally unstable model of cavernous weathering systems outcrop surfaces displaying caverns tend to show increasing fragmentation of the surface in the early stages of cavernous weathering succeeded by convergent evolution of the surface in which caverns tend to grow and coalesce a paradoxical relationship exists between the weathering system output at the scale of individual forms and the outcrop scale caverns tend toward minimum interior surface area by developing a spheroidal form yet the outcrop surface tends toward maximum exposed surface area by increasing the degree of fragmentation of the surface copyright 2004 john wiley sons ltd

on the interaction of geology measurement and statistical analysis of small scale permeability measurements sedimentary rocks exhibit small scale mm permeability variations which can be detected with a probe permeameter the structure of the laminations may provide evidence about the characteristics of the measurement device the statistical interpretation of these measurements using averages and variograms is enhanced when the geological character of the rock is taken into consideration the three aspects of rock characterization namely geology measurement and statistical analysis are best assessed in concert this theme is illustrated using probe data taken from sections of the rannoch and etive formations northern north sea

numerical simulations of a gravity wave event over ccope part ii waves generated by an orographic density current a mesoscale numerical model and detailed observations are used to investigate the generation and maintenance of a mesoscale gravity wave event observed in eastern montana on 11 july 1981 during the cooperative convective precipitation experiment ccope it is shown that the interaction between an orographic density current and a mountain barrier leads to the generation of the gravity waves the simulation results suggest the following four stage conceptual model during stage i shortly after sunset the remnant up branch of a thermally driven upslope flow east of the rockies was driven back toward the mountain by the pressure gradient force associated with a cool pool over north dakota the nocturnal stable layer over eastern montana was strengthened during passage of this density current during the 1 2 h transition period of stage ii the advancing density current became blocked as it encountered the higher terrain an isentropic ridge developed above the original warm lee trough due to strong adiabatic cooling caused by the sustained upward motion in the presence of orographic blocking during stage iii an even stronger upward motion center formed to the east of the density current head updraft in response to an eastward horizontal pressure gradient force produced by the isentropic ridge in stage iv as the density current head collapsed and downward motion developed to the west of the original updraft in quadrature phase with the isentropic perturbation a gravity wave was generated this wave propagated eastward with the mean wind opposite to the motion of the earlier density current and was maintained by the strong wave duct established earlier by the density current thus the mountain plains circulation may at times generate mesoscale gravity waves and deep convection hours after diurnal heating has ended

circum mediterranean fire activity and climate changes during the mid holocene environmental transition 8500 2500 cal bp a mid to late holocene synthesis of fire activity from the mediterranean basin explores the linkages among fire climate variability and seasonality through several climatic and ecological transitions regional fire histories were created from 36 radiocarbon dated sedimentary charcoal records available from the global charcoal database during the mid holocene thermal maximum around 7500 4500 cal bp charcoal records from the northern mediterranean suggest an increase in fire while records from the southern mediterranean indicate a decrease associated with wetter than present summers a north south partition between 40 and 43 n latitude is apparent in the central and western mediterranean relatively abrupt changes in fire activity are observed c 5500 5000 cal bp records of holocene fire activity appear sensitive to both orbitally forced climate changes and shorter lived excursions which may be related to north atlantic cold events possibly modulated by an nao like climate mechanism in cases wh

experimental salt weathering of limestones in relation to rock properties a total of 21 different types of british and european mesozoic limestones have been subjected to simulated salt weathering using sodium sulphate na2so4 with the following aims assessment of the relative durabilities of different types of limestone assessment of the importance of modulus of elasticity and other factors in affecting durability and assessment of the use of impulse excitation techniques to monitor changes in rock modulus of elasticity the rocks showed a wide spectrum of durabilities while rocks with high values of modulus of elasticity lower water absorption capacities high densities and low salt uptakes tended to be durable there were anomalies the explanation for which probably lies in their pore structures non destructive testing techniques showed that although the more durable rocks failed to lose weight or to show visual signs of disintegration their modulus of elasticity values did tend to decline indicating a loss in strength copyright 1999 john wiley sons ltd

comparative investigation of the spatial distribution of past weathering impacts on sandstone masonry abstract inspection of the deterioration of both natural outcrops and historical built stone facades reveals that patterns of disruption are not uniform indicating the influence of material and environmental properties sandstones have a spatial variability in weathering response for this reason geostatistical techniques have been applied to studies of sandstone properties mineralogical and structural that influence susceptibility to decay for this study a comparative analysis of permeability data acquired from a quarry fresh stone and a weathered sample is undertaken the depositional processes that resulted in the formation of sandstone also create structures of spatial variation such as laminations or larger bedding planes within the material using geostatistical techniques the permeability variance observed within quarry fresh blocks of sandstone indicates the subsampling of larger geological structures when cut from the quarry face once blocks have been emplaced within a building they will be subjected to the increased stress of the urban environment these conditions result in exacerbated weathering through processes such as salt and chemical weathering weathering can alter material properties such as permeability with the creation of a secondary permeability produced by the opening pores and alteration of pore connectivity through the application of geostatistics in the analysis of permeability data observed from the weathered block variography reveals the presence of smaller scale structures this suggests that alteration of the sandstone s permeability has led to the creation of new weathering structures within the stone overwriting the initial sedimentary structures these weathering related structures will affect both the magnitude and spatial distribution of permeability within the weathered block the interconnected pathways of permeability created by past weathering facilitate the migration of moisture and salts in solution through the substrate this work has demonstrated that through a geostatistical approach with the application of co kriging these potential moisture pathways can be identified and visualised

preliminary observations on the impact of complex stress histories on sandstone response to salt weathering laboratory simulations of process combinations historic sandstone structures carry an inheritance or a memory of past stresses that the stone has undergone since its placement in a facade this inheritance which conditions present day performance may be made up of long term exposure to a combination of low magnitude background environmental factors for example salt weathering temperature and moisture cycling and superimposed upon these less frequent but potentially high magnitude events or exceptional factors for example lime rendering severe frost events fire the impact of complex histories on the decay pathways of historic sandstone is not clearly understood but this paper seeks to improve that understanding through the use of a laboratory process combination study blocks of quartz sandstone peakmoor from nw england were divided into subsets that experienced different histories lime rendering and removal fire and freeze thaw cycles in isolation and combination that reflected the event timeline of a real medieval sandstone monument in ne ireland bonamargy friary mccabe et al 2006b these subsets were then subject to salt weathering cycles using a 10 salt solution of nacl and mgso4 that represents the every day stress environment of for example sandstone structures in coastal or polluted urban location block response to salt weathering was monitored by collecting drying and weighing the debris that was released as blocks were immersed in the salt solution at the beginning of each cycle the results illustrate the complexity of the stone decay system showing that seemingly small variations in stress history can produce divergent response to salt weathering cycles applied to real world historic sandstone structures this concept may help to explain the spatial and temporal variability of sandstone response to background environmental factors on a single facade and encourage conservators to include the role of stress inheritance when selecting and implementing conservation strategies

sandstone response to salt weathering following simulated fire damage a comparison of the effects of furnace heating and fire fire has long been recognized as an agent of rock weathering our understanding of the impact of fire on stone comes either from early anecdotal evidence or from more recent laboratory simulation studies using furnaces to simulate the effects of fire this paper suggests that knowledge derived from simulated heating experiments is based on the pre conceptions of the experiment designer when using a furnace to simulate fire the operator decides on the maximum temperature and the duration of the experiment these are key factors in determining the response of the stone to fire and if these are removed from real world observations then knowledge based on these simulations must be questioned to explore the differences between heating sandstone in a furnace and a real fire sample blocks of peakmoor sandstone were subjected to different stress histories in combination lime rendering and removal furnace heating or fire frost and salt weathering block response to furnace heating and fire is discussed with emphasis placed on the non uniformity of the fire and of block response to fire in contrast to the uniform response to surface heating in a furnace subsequent response to salt weathering by a 10 solution of sodium chloride and magnesium sulphate was then monitored by weight loss blocks that had experienced fire showed a more unpredictable response to salt weathering than those that had undergone furnace heating spalling of corners and rapid catastrophic weight loss were evidenced in blocks that had been subjected to fire after periods of relative quiescence an important physical side effect of the fire was soot accumulation which created a waxy relatively impermeable layer on some blocks this layer repelled water and hindered salt ingress but eventually detached when salt able to enter the substrate through more permeable areas concentrated and crystallized behind it resulting in rapid weight loss and accelerated decay copyright 2007 john wiley sons ltd

rock warming and drying under simulated intertidal conditions part i experimental procedures and comparisons with field data the wetting drying and warming cooling behaviours of rock and stone are known to influence the nature and rate of weathering the way materials warm up and dry out also influences their suitability as biological substrata while rock thermal behaviours have been measured under controlled laboratory conditions previous experiments have largely been restricted to terrestrial simulations due to practical constraints where efforts have been made to simulate intertidal conditions expansion and contraction of rocks or rates of breakdown i e sediment production and weight loss have been measured while detailed observations of thermal and drying behaviours have rarely been made a simple semi automated procedure is described that enabled measurement of surface temperatures and desorption evaporative water loss for different material types rock and concrete under simulated semidiurnal tide conditions some preliminary results are presented illustrating the types of data that were obtained and comparisons are made with temperature data collected on a rock platform in the uk to assess the ability of the procedure to adequately represent field conditions copyright 2011 john wiley sons ltd

variable weathering response in sandstone factors controlling decay sequences differences in weathering response characteristics of fine and coarse grained stanton moor sandstone samples were assessed in a laboratory weathering simulation experiment using a variable combination of salt weathering and freeze thaw cycles preliminary analysis of permeability characteristics identified similar mean values for each type of stanton sandstone but significant differences in the range of values between the two sample sets with coarse grained samples of stanton moor sandstone displaying a restricted range of values in comparison to fine grained samples which showed much greater within block variation data indicated that the greater the range in initial permeability values the greater the potential for salt and moisture ingress and retention and hence eventual disruption of the fabric of the stone experimental data also identified different stages in decay sequences with significant structural change occurring during the initial preparatory stage before material breakdown and loss became apparent evidence suggests that relatively minor structural and mineralogical differences between samples of the same stone type can have a significant influence on weathering behaviour resulting in distinct rates and patterns of breakdown copyright 2005 john wiley sons ltd

abrupt climate variability since the last deglaciation based on a high resolution multi proxy peat record from nw iran the hand that rocked the cradle of civilization abstract we present a high resolution sub decadal to centennial multi proxy reconstruction of aeolian input and changes in palaeohydrological conditions based on a 13000 yr record from neor lake s peripheral peat in nw iran variations in relative abundances of refractory al zr ti and si redox sensitive fe and mobile k and rb elements total organic carbon toc 13 c toc compound specific leaf wax hydrogen isotopes d carbon accumulation rates and dust fluxes presented here fill a large gap in the existing terrestrial paleoclimate records from the interior of west asia our results suggest that a transition occurred from dry and dusty conditions during the younger dryas yd to a relatively wetter period with higher carbon accumulation rates and low aeolian input during the early holocene 9000 6000 yr bp this period was followed by relatively drier and dustier conditions during middle to late holocene which is consistent with orbital changes in insolation that affected much of the northern hemisphere numerous episodes of high aeolian input spanning a few decades to millennia are prevalent during the middle to late holocene wavelet analysis of variations in ti abundances as a proxy for aeolian input revealed notable periodicities at 230 320 and 470 years with significant periodicities centered around 820 1550 and 3110 years over the last 13000 years comparison with palaeoclimate archives from west asia the north atlantic and african lakes point to a teleconnection between north atlantic climate and the interior of west asia during the last glacial termination and the holocene epoch we further assess the potential role of abrupt climate change on early human societies by comparing our record of palaeoclimate variability with historical geological and archaeological archives from this region the terrestrial record from this study confirms previous evidence from marine sediments of the arabian sea that suggested climate change influenced the termination of the akkadian empire in addition nearly all observed episodes of enhanced dust deposition during the middle to late holocene coincided with times of drought famine and power transitions across the iranian plateau mesopotamia and the eastern mediterranean region these findings indicate that while socio economic factors are traditionally considered to shape ancient human societies in this region the influence of abrupt climate change should not be underestimated

holocene sedimentology of hypersaline lake urmia northwestern iran abstract a limnogeological expedition examined the sedimentary record of lake urmia one of the world s largest saline lakes located in a tectonically active arid intermontane plateau in northwestern iran near the cradle of western civilization lake urmia resembles the great salt lake u s a in many respects of morphology water chemistry and sediments the present lake area is about 5000 km 2 shallow 8 12 m and a perennial sodium chloride sulfate system 22 salts high resolution 3 5 khz seismic profiles show morphological relicts from a desiccation playa phase buried below only a few meters of sediments from lacustral phases in places around the deeper areas the lake floor is not smooth but covered with mounds aligned in prevailing current directions these are erosional relicts rather than bioherms sediments comprise aragonite chemical precipitates fecal pellet sands detrital clayey muds thin aragonite crusts oolites various gypsum types and occurrences of dolomite in peripheral areas organic matter characteristic of the present shorelines is not preserved at depth in basinal areas piston cores up to 6 m long penetrated a holocene sequence of hypersaline facies with laminated aragonite fecal pellet muds and bottomed in a playa mudflat facies with central gypsiferous muds and marginal terrigenous to dolomitic muds preliminary radiocarbon and pollen analyses suggest a playa stage prior to 9000 yr b p with saline lake deposition in a cool arid climate from 9000 to 7500 yr b p higher energy facies prevailed in a shallow saline lake and since then present day saline environments have persisted with evidence of numerous second order water level fluctuations the preliminary results suggest a lake system out of phase with north african and some other middle eastern lakes

aeolian control on the deposition of high altitude lacustrine basins in the middle east the case of lake neor nw iran abstract lake neor is the largest lacustrine basin in the high mountains of the middle east at 2500 m altitude in the alborz belt this lake of holocene age is a shallow fresh water body of glacial origin with ca 4 km 2 surface area and a 40 km 2 drainage area its sedimentary sequence comprised of peat and gyttja consists of 10 m infill which is fairly thick for such a lake autochthonous organic matter is limited in and around the lake except for small areas at the northern and southern ends inorganic constituents of the infill sediment include a significant amount of fine grained calcite dolomite and mica particles that are exotic to the catchment they do not occur in the source rocks as the drainage area of the lake is composed of only andesites and trachyandesites of eocene age in addition the uppermost part of the infill includes abundant fine grained charcoal particles derived from large forest fires perhaps derived as far as the mediterranean region as shown by the present meteorological records the sediment of lake neor is under aeolian control during dust storms this is leading to a considerable amount of deposition air borne particles the infill of some lakes particularly those in highlands may have contain an important aeolian component and thus they cannot be used directly for the interpretation of the evolution of the palaeogeography without taking into consideration the role of dust storms on deposition

sedimentary evolution and environmental history of lake van turkey over the past 600 000 years the lithostratigraphic framework of lake van eastern turkey has been systematically analysed to document the sedimentary evolution and the environmental history of the lake during the past ca 600 000 years the lithostratigraphy and chemostratigraphy of a 219 m long drill core from lake van serve to separate global climate oscillations from local factors caused by tectonic and volcanic activity an age model was established based on the climatostratigraphic alignment of chemical and lithological signatures validated by 40ar 39ar ages the drilled sequence consists of ca 76 lacustrine carbonaceous clayey silt ca 2 fluvial deposits ca 17 volcaniclastic deposits and 5 gaps six lacustrine lithotypes were separated from the fluvial and event deposits such as volcaniclastics ca 300 layers and graded beds ca 375 layers and their depositional environments are documented these lithotypes are i graded beds frequently intercalated with varved clayey silts reflecting rising lake levels during the terminations ii varved clayey silts reflecting strong seasonality and an intralake oxic anoxic boundary for example lake level highstands during interglacials interstadials iii caco3 rich banded sediments which are representative of a lowering of the oxic anoxic boundary for example lake level decreases during glacial inceptions iv caco3 poor banded and mottled clayey silts reflecting an oxic anoxic boundary close to the sediment water interface for example lake level lowstands during glacials stadials v diatomaceous muds were deposited during the early beginning of the lake as a fresh water system and vi fluvial sands and gravels indicating the initial flooding of the lake basin the recurrence of lithologies i to iv follows the past five glacial interglacial cycles a 20 m thick disturbed unit reflects an interval of major tectonic activity in lake van at ca 414 ka bp although local environmental processes such as tectonic and volcanic activity influenced sedimentation the lithostratigraphic pattern and organic matter content clearly reflect past global climate changes making lake van an outstanding terrestrial archive of unprecedented sensitivity for the reconstruction of the regional climate over the last 600 000 years

the thermal circulation of a grand plateau sensitivity to the height width and shape of the plateau abstract idealized numerical simulations are presented to investigate the sensitivity of the thermal plateau circulation to the plateau height width and the presence of a mountain ridge encompassing the plateau the study concentrates on plateaus surrounded by land with the same surface properties so that the topography is the only source of differential heating for low plateaus it is found that the strength of the plateau circulation increases with the plateau height because the excess heating of the plateau increases with its height the plateau circulation reaches its maximum strength for plateau heights similar to the mixed layer depth over the surrounding lowlands for even higher plateaus the depth of the circulation decreases whereas the peak intensity exhibits little change the plateau height also controls the temporal evolution of the plateau circulation for low plateaus low level inflow is primarily found during the night because convection cells forming over the lateral slopes prevent a

regional impact of an elevated heat source the zagros plateau of iran the authors propose that a heat driven circulation from the zagros plateau has a significant impact on the climate of the middle east plain mep especially summertime winds air temperature and aridity this proposal is examined in numerical experiments with a regional climate model simulations in which the zagros plateau was assigned a highly reflective snowlike albedo neutralized the heat driven circulation and produced an extra summertime warming of 1 2 c in the mep measured relative to a control simulation and to the records of the ncep ncar reanalysis project this effect was largest in midsummer when heating on the plateau was greatest additionally simulations with high albedo on the zagros showed reduced subsidence and enhanced precipitation in the mep these sensitivities are interesting because the zagros plateau lies downwind of the mep analysis of model results indicates that the sensitivity of the upwind subsidence region to zagros albedo can be understood as a linear atmospheric response to plateau heating communicated upwind by a steady heat driven circulation that influences the thermodynamic balance of the atmosphere this regional phenomenon adds to the large scale subsidence patterns established by the hadley circulation and the asian monsoon observed patterns of vertical motion in the middle east then are a combined product of zagros induced subsidence and hemispheric scale circulations

boundary layer evolution and regional scale diurnal circulations over the and mexican plateau data collected in a measurement campaign in february and march 1997 showed that the mexico basin also called the valley of mexico located atop the mexican plateau fails to develop the strong nocturnal inversions usually associated with basins and does not exhibit diurnally reversing valley wind systems data analyses two and three dimensional numerical simulations with the regional atmospheric modeling system rams and a lagrangian particle dispersion model are used to interpret these observations and to examine the effects of topography and regional diurnal circulations on boundary layer evolution over the mexico basin and its surroundings during fair weather periods in the winter dry season we show that the boundary layer evolution in and above the basin is driven primarily by regional diurnal circulations that develop between the air above the mexican plateau and the generally cooler surrounding coastal areas a convective boundary layer cbl grows explosively over the plateau in the late morning to reach elevations of 2250 m agl 4500 m msl by noon and a strong baroclinic zone forms on the edges of the plateau separating the warm cbl air from its cooler surroundings in early afternoon the rates of heating and cbl growth are slowed as cool air leaks onto the plateau and into the basin through passes and over low lying plateau edges the flow onto the plateau is retarded however by the strongly rising branch of a plain plateau circulation at the plateau edges especially where mountains or steep slopes are present an unusually rapid and deep cooling of the air above the plateau begins in late afternoon and early evening when the surface energy budget reverses the cbl decays and air accelerates onto the plateau through the baroclinic zone flow convergence near the basin floor and the associated rising motions over the basin and plateau produce cooling in 3 hours that is equivalent to half the daytime heating while the air that converges onto the plateau comes from elevations at and above the plateau it is air that was modified earlier in the day by a cool moist coastal inflow carried up the plateau slopes by the plain plateau circulation

characteristics of dust deposited along a transect between central iran and the zagros mountains abstract few studies have been reported on the characteristics of dust particles deposited in arid regions of the middle east the objective of this study was to identify the variations in physical chemical and mineralogical composition of dust particles deposited along an elevational transect lying between central iran and the zagros mountains in the west dust samples were collected at 12 localities during september 2008 and july 2009 with and without transboundary dust storms respectively samples were examined for their grain size distribution and their mineralogical and chemical composition surface soils were also sampled from the vicinity of the dust sampling sites and their total elemental compositions were determined the results indicated that dust deposition rate mean particle diameter and concentration of soluble ions in samples from both sampling periods decreased with altitude with a significantly lower gradient for samples of july 2009 than for those of september 2008 the similarity observed in dust samples taken during september 2008 and those reported by previous studies or measured in local soils and sediments suggests that local soils greatly contribute to the atmospheric dust along the transect in periods with no dust storms during such periods dust deposits in the high altitude zagros mountains where annual precipitation is higher and temperature lower only receive a minor contribution from arid soils of central iran however in july 2009 when a heavy dust storm took place significant differences were observed between local soils and dust samples along the transect particularly at high altitudes in terms of their physicochemical and mineralogical characteristics these findings together with satellite images and patterns of wind frequency and direction clearly indicate the major contribution of a transboundary dust storm probably originating from iraqi arid land to atmospheric deposition in the zagros area and central iran when dust storms blow from across the borders the contribution of local soils and sediments to aerosols drastically decreases with elevation if dust storms originating from outside the country continue to occur not only will they influence the surface soil properties in the zagros region but will also induce environmental problems in the region

sandstone weathering a century of research and innovation abstract a review of sandstone weathering research particularly in the past 100 years reveals a trajectory of enquiry from early description and classification of features to development of process based explanations to decreasing scales of investigation and a disparity between understanding of process es and explanations of the genesis of sandstone weathering features developments in expositions on mesoscale weathering features on sandstone surfaces are discussed demonstrating a range of approaches to weathering phenomena field based and laboratory based that must be linked to provide an explanation of observed features on a landform scale throughout the twentieth century a thematic chronology highlights certain trends in research description of forms often in arid and semi arid environments single process form models an emphasis on experimentation difficulties in measuring weathering rates and a persistent emphasis on physical causes of breakdown a new research agenda is promoted in which biodeterioration and chemical processes gain parity a holistic approach based on conceptual modeling of weathering systems gains prominence and scale issues are addressed more rigorously

dynamical instability in surface permeability characteristics of building sandstones in response to salt accumulation over time abstract this paper explores how the surface permeability of sandstone blocks changes over time in response to repeated salt weathering cycles surface permeability controls the amount of moisture and dissolved salt that can penetrate in and facilitate decay connected pores permit the movement of moisture and hence soluble salts into the stone interior and where areas are more or less permeable soluble salts may migrate along preferred pathways at differential rates previous research has shown that salts can accumulate in the near surface zone and lead to partial pore blocking which influences subsequent moisture ingress and causes rapid salt accumulation in the near surface zone two parallel salt weathering simulations were carried out on blocks of peakmoor sandstone of different volumes blocks were removed from simulations after 2 5 10 20 and 60 cycles permeability measurements were taken for these blocks at a resolution of 20 mm providing a grid of 100 permeability values for each surface the geostatistical technique of ordinary kriging was applied to the data to produce a smoothed interpolation of permeability for these surfaces and hence improve understanding of the evolution of permeability over time in response to repeated salt weathering cycles results illustrate the different responses of the sandstone blocks of different volumes to repeated salt weathering cycles in both cases after an initial subtle decline in the permeability reflecting pore blocking the permeability starts to increase reflected in a rise in mean maximum and minimum values however between 10 and 20 cycles there is a jump in the mean and range permeability of the group a block surfaces coinciding with the onset of meaningful debris release after 60 cycles the range of permeability in the group a block surface had increased markedly suggesting the development of a secondary permeability the concept of dynamic instability and divergent behaviour is applied at the scale of a single block surface with initial small scale differences across a surface having larger scale consequences as weathering progresses after cycle 10 group b blocks show a much smaller increase in mean permeability and the range stays relatively steady this may be explained by the capillary conditions set up by the smaller volume of the stone allowing salts to migrate to the back of the blocks and effectively relieving stress at the front face