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

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

seismicity in the vicinity of the snorcle corridors of the northern canadian cordillera the slave northern cordillera lithospheric evolution snorcle corridors of the northern cordillera sample some of the most and least seismically active regions of canada the earthquake history of this region is short precise determination of earthquake locations and depths is not possible even today nonetheless significant gains in our knowledge of the seismicity of this region have been made in recent years from studies of historic earth quakes microseismicity studies and advances in waveform modelling techniques combined with broadband data that allow for determination of focal mechanisms and depths for moderate earthquakes this article summarizes our current knowledge of the seismicity and seismic hazards across the region these detailed analyses have shown that i the largest historical earthquakes have occurred in regions of ongoing microseismicity ii the largest earthquakes have occurred in pairs or in swarms suggesting that stress triggering is important in this region iii the active faults are concentrated in the offshore region iv there is a concentration of seismicity in the fold and thrust belt several hun dred kilometres from the active plate margin and v there is no seismicity associated with the quaternary volcanic zone in northern british columbia potentially damaging magnitude m 5 earthquakes can be expected every few years in the vicinity of the northern cordillera the mw 7 9 denali alaska earthquake where mw is the moment magnitude was a good reminder that the effects of a large earthquake can be substantial even hundreds of kilometres from the epicentre detailed studies of seismicity earth structure and tectonics with the latter made possible in large part by the snorcle transect will allow for informed decision making for resource development and the design of safe structures and infrastructure in the northern canadian cordillera resume les corridors du projet snorcle de la cordillere septentrionale permettent d echantillonner quelques unes des regions sismiques les plus et les moins actives du canada l histoire des seismes de cette region est breve meme

weathering by wetting and drying some experimental results a series of experiments on sandstone and dolerite was undertaken in an attempt to better understand the wetting and drying weathering process as rock samples are frequently subjected to wet dry cycles within the simulation of other weathering mechanisms e g freeze thaw three common methods of moisture application were used and the influences of these evaluated it was found that the method of moisture application could affect the nature of the weathering products resulting from wetting and drying it was also observed that there were changes in the internal properties of the rock e g porosity microporosity and that these could influence the synergistic operation of other weathering processes although not all of the observations could be explained it is apparent that wetting and drying has both a direct and an indirect effect on the weathering of rock that has not been taken into account in simulations greater cognizance needs to be given to the role of this process both in the field and in laboratory simulations

lichen hotspots raised rock temperatures beneath verrucaria nigrescens on limestone abstract field exposure trials and laboratory experiments are integrated to compare surface and internal temperature changes of limestone with an epilithic verrucaria nigrescens and endolithic verrucaria baldensis covering of lichens and with no lichen cover control blocks with covering of v nigrescens experience both the highest surface and internal temperatures under a direct heating source during daytime and in laboratory experiments spectrophotometer data suggest that the black colour of the v nigrescens thallus plays a significant role in determining the thermal response of the rock surface when direct heating by sun or lamp is absent at nighttime and for a diurnal cycle programmed in an environmental chamber little differentiation occurs between surface and internal temperatures for all surface types compared for all blocks exposed maximum rates of daytime surface temperature change ranged from 1 47 to 3 04 c min 1 and for two of the exposure periods the highest rates of daytime surface temperature change were experienced by blocks with v nigrescens cover the blocks with v nigrescens cover also experience the greatest thermal gradients in both field and laboratory experiments the rates of surface temperature change and thermal gradients experienced beneath v nigrescens in this study could be significant in increasing rock susceptibility to breakdown

salt weathering influence of evaporation rate supersaturation and crystallization pattern micro and macroscale experiments which document the dynamics of salt damage to porous stone have yielded data which expose weaknesses in earlier interpretations previously unexplained differences are found in crystal morphology crystallization patterns kinetics and substrate damage when comparing the growth of mirabilite na2so4 10h2o and thenardite na2so4 versus halite nacl the crystallization pattern of sodium sulphate was strongly affected by relative humidity rh while a lesser rh effect was observed for sodium chloride macroscale experiments confirmed that mirabilite crystallizing at rh 50 per cent and thenardite crystallizing at rh 50 per cent tend to form subflorescence in highly localized areas under conditions of constant rh and temperature this crystallization pattern was more damaging than that of halite since halite tended to grow as efflorescence or by filling the smallest pores of the stone in a homogeneous fashion a result which contradicts wellman and wilson s theoretical model of salt damage low rh promoted rapid evaporation of saline solutions and higher supersaturation levels resulting in the greatest damage to the stone in the case of both sodium sulphate and sodium chloride crystallization at any particular crystallization condition sodium chloride tended to reach lower supersaturation levels resulting in the crystallization of isometric crystals and created negligible damage while sodium sulphate reached higher supersaturation ratios resulting in non equilibrium crystal shapes resulting in significant damage esem showed no damage from sodium sulphate due to hydration instead after water condensation on thenardite crystals rapid dissolution followed by precipitation of mirabilite took place resulting in stone damage by means of crystallization pressure generation it is concluded that salt damage due to crystallization pressure appears to be largely a function of solution supersaturation ratio and location of crystallization these key factors are related to solution properties and evaporation rates which are constrained by solution composition environmental conditions substrate properties and salt crystallization growth patterns when combined with a critical review of salt damage literature these experiments allow the development of a model which explains variations in damage related to combinations of different salts substrates and environmental conditions

new insights into rock weathering from high frequency rock temperature data an antarctic study of weathering by thermal stress a major limitation of many weathering studies has been the acquisition of rock temperature data at insufficiently frequent intervals for the meaningful determination of the rate of change of temperature t t equipment and or logistical constraints frequently facilitate temperature measurement at only hourly intervals or at best every 10 min such data are not adequate for the determination of t t required for the evaluation of the freeze thaw mechanism or thermal stress fatigue recent undertakings at different sites in antarctica and at other cold region locations provide rock temperature measurements at 1 min intervals which indicate that the perception of the weathering regime would be very different from that generally assumed from longer interval geomorphological data these data clearly show that thermal stress fatigue and thermal shock may be more active components of the antarctic weathering regime than have generally been recognised the aridity of the study area limits the role of freeze thaw weathering values of t t of 2 c min 1 that suggest thermal stress fatigue shock is operative were recorded observations of rock flaking are thought to reflect the impact of thermal stress further the data show that contrary to general perceptions the southern aspect can in summer experience higher rock surface temperatures than the north facing exposure an examination of rock fracture patterns found in the field shows great similarity to fracture patterns developed in the laboratory as a direct result of thermal shock the argument is made that greater cognizance should be given to thermal effects

blue green algae and terrestrial limestone weathering on aldabra atoll an s e m and light microscope study blue green algae have been observed to affect limestone weathering on aldabra atoll indian ocean three different habitats can be identified on the rock surface i e epilithic chasmolithic and endolithic algae in each habitat may affect weathering in various ways samples of blue green algae and rock were taken from various terrestrial and coastal environments on aldabra atoll samples of limestone tablets and calcite crystals after one year in situ were also studied light and s e m microscopy revealed that endolithic boreholes were present on many samples especially those from frequently wetted sites to a maximum depth of 800 m an altered zone of micrite and algal filaments was also discovered in many samples from morphological and petrographical evidence blue green algal influences on weathering on aldabra atoll seem to be very complex and cannot easily be related to small scale landforms

observations of three dimensional salt distribution in building sandstone observations of three dimensional salt distributions within three sandstone blocks after 120 years of exposure in an aggressive urban environment are presented based on measurements of soluble ion concentrations results indicate a complex distribution of sulphur and chloride where distributions are not consistent between salt types dictated by conditions at the six surfaces of the blocks this highlights the dangers of extrapolating the results of salt weathering simulations with regard to salt accumulation patterns or the results of fieldwork which rely on single surface samples from individual stones the widely held perception that urban environments are dry with shallow surface wetting of building stone does not appear to hold true for certain building stone copyright 2000 john wiley sons ltd

surface swelling of coastal bedrock on inter tidal shore platforms kaikoura peninsula south island new zealand this paper reports the occurrence of swelling of coastal bedrock measured with a traversing micro erosion meter tmem on inter tidal mudstone and limestone shore platforms while numerous micro erosion meter mem studies have been made only a small number have reported surface swelling during this study 24 055 measurements were made with a tmem of those 4047 indicated swelling or 17 of the total number of measurements vertical swelling of up to 8 9 mm was measured and values of 3 and 4 mm were common swelling displayed a complex pattern with minor swelling being superimposed on longer period episodes duration of swelling events in excess of 697 days were recorded while other events were commonly in the order of 3 to 4 months there is a distinct seasonal variation with greater and more frequent swelling occurring during summer months compared with winter explanation for swelling includes the growth of salt crystals in rock lattices and expansion from wetting and drying warm summer temperatures provide the best conditions for both processes swelling appears to be an important precursor to erosion of material from shore platform surfaces the conclusion drawn is that subaerial weathering makes an important contribution to the lowering of the shore platforms on the kaikoura peninsula

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

an investigation into the relationship between salt weathering debris production and temperature an investigation using laboratory simulation has been made using air temperature data for tunisia antarctica and southwest england an experiment with a 50 cycle run produced results which showed significantly greater debris production in the antarctica and tunisian simulations than in the southwest england simulation using x ray analysts to determine salt penetration an inverse relationship between salt penetration and debris production was seen to exist this could be the result of evaporation in the tunisian simulation and rapid freezing in the antarctic simulation concentrating salts in the upper layers of the rock samples in the southwest england simulation no freezing and relatively high humidities allowed greater penetration thus distributing an equal input of salt over a greater area the author tentatively suggests the possible existence of a parabolic relationship between salt weathering and temperature

systematics and taxonomic diversity of squamates from the upper cretaceous djadochta formation bayan mandahu gobi desert people s republic of china squamate fossils collected for the sino canadian dinosaur expeditions 1986 1990 include some 70 specimens from the upper cretaceous campanian djadochta formation exposed at the vicinity of bayan mandahu inner mongolia china well preserved skulls jaws postcranial skeletons and even osteodermal armor document a fossil assemblage composed of at least 18 genera in 8 families besides showing considerable taxonomic diversity several families recorded in the assemblage are of importance in understanding the geologic and biogeographic distribution of the relevant groups and the paleoenvironment in which these lizards lived comparison of the gobi lizard assemblage with north american and central asian assemblages is briefly discussed taxonomic differences in the assemblage from that of the upper cretaceous in the north american western interior reflect endemism and suggest a low frequency of interchange of small terrestrial vertebrates between the two regions during campanian time the taphonomic s

spatial characterization of salt accumulation in early stage limestone weathering using probe permeametry this research characterizes the weathering of natural building stone using an unsteady state portable probe permeameter variations between the permeability properties of fresh rock and the same rocks after the early stages of a salt weathering simulation are used to examine the effects of salt accumulation on spatial variations in surface rock permeability properties in two limestones from spain the fraga and tudela limestones are from the ebro basin and are of miocene age both stone types figure largely in the architectural heritage of spain and in common with many other building limestones they are prone to physical damage from salt crystallization in pore spaces to examine feedbacks associated with salt accumulation during the early stages of this weathering process samples of the two stone types were subjected to simulated salt weathering under laboratory conditions using magnesium sulphate and sodium chloride at concentrations of 5 and 15 permeability mapping and statistical analysis aspatial statistics and spatial prediction before and after salt accumulation are used to assess changes in the spatial variability of permeability and to correlate these changes with salt movement porosity change potential rock deterioration and textural characteristics statistical analyses of small scale permeability measurements are used to evaluate the drivers for decay and hence aid the prediction of the weathering behaviour of the two limestones copyright 2010 john wiley sons ltd

tidal wetting and drying on shore platforms an experimental study of surface expansion and contraction laboratory experiments have been conducted to measure rock expansion and contraction induced by wetting and drying on intertidal shore platforms in eastern canada almost 800 rock cores and cubes were subjected to between 800 and 1000 tidal cycles the rocks were put into tidal simulators and inundated in de ionized water for 1 6 or 11 h of each 12 h cycle replicating conditions at the high mid and low tidal levels respectively micro erosion meter mem stations were also installed in slabs of argillite sandstone and basalt the slabs were subjected to conditions at the high mid and low tidal levels and a traversing mem was used to measure rock expansion and contraction as the slabs dried in air with variable temperature and humidity during low tide the slabs were also exposed for long periods to air with variable humidity cores and cubes often gained in weight when they absorbed or adsorbed water and retained it for periods ranging from 1 month to 1 year or more although this did not appear to be a prelude to rock breakdown tidal wetting and drying and exposure to humid air caused the argillite and basalt slabs to expand and contract by up to 0 14 and 0 04 mm respectively wetting and drying did not induce expansion or contraction of the sandstone but the sandstone did respond slightly to changes in air humidity the greatest amount of expansion and contraction was at the high tidal level in the argillite and at the mid tidal level in the basalt which is consistent with previously measured rates of downwearing

frost weathering and the saturation of coastal rocks measurements were made of the water content in coastal rocks by simulating tidal oscillations in the laboratory and by field measurement in eastern canada if rapid freezing takes place upon exposure to the air saturation levels may be high enough to permit frost weathering in fine grained rocks in the lower portions of the intertidal zone near the high tidal level however it may be dependent upon a supply of water from the ice foot and from melting snow if freezing is slow frost action may be inhibited by desorption of the rocks while they are exposed by the ebb tide there was no evidence of a level of permanent sea water saturation within the intertidal zone ambient temperature and humidity may affect the rate of rock desorption

microclimate and weathering in the central namib desert namibia data on rock surface microclimates at four sites kleinberg vogelfederberg gobabeb and ganab along a transect across the central namib desert over a 3 year period have been collected alongside some shorter term data sets rock surface temperature rst air temperature wind relative humidity and surface wetness data are presented here weathering of exposure blocks of local marble and granite has also been monitored over the 3 year period with change observed visually and with scanning electron microscopy complex temporal patterns of rock temperature fluctuations are observed over the 3 years although the four sites show very similar overall trends suggesting spatial homogeneity in the rock surface temperature regime relative humidity and surface wetness data show clear differences between the four sites related to the frequency of fogs granite blocks show no visible changes after 2 years of weathering whereas marble blocks especially those at ganab show sem evidence of structural weakening after 1 year

tidal wetting and drying on shore platforms an experimental assessment abstract rocks were subjected to wetting and drying cycles with de ionized water under real time conditions using tidal simulators one third of the samples experienced 11 h of exposure and 1 h of inundation over a 12 h tidal cycle representing high tidal conditions one third experienced 6 h of exposure and 6 h of inundation representing mid tidal conditions and one third experienced 1 h of exposure and 11 h of inundation representing low tidal conditions we obtained 324 cores from igneous metamorphic and sedimentary rocks from ontario which were exposed to more than 930 wetting and drying cycles over 16 months we obtained 675 cores and cubes from basalts sandstones and argillites from shore platforms in eastern canada which were exposed to about 700 cycles over 12 months many of the cores and cubes experienced very little to no breakdown particularly those from the igneous and metamorphic rocks of ontario sandstones from a sloping platform in the macrotidal bay of fundy and argillites from a horizontal mesotidal platform in gaspe quebec were the most susceptible rock types with equivalent surface downwearing rates ranging from 0 to 4 mm year 1 the results suggest that downwearing rates decrease with elevation within the intertidal zone probably because rocks require much longer to desorb than to absorb water the experiments demonstrated that wetting and drying can be an important process on shore platforms in some types of rock helping to lower the height and reduce the gradient of sloping macrotidal platforms and to reduce the height of horizontal micro and mesotidal platforms

patterns of surface downwearing on shore platforms in eastern canada downwearing rates were measured on shore platforms at about 200 transverse micro erosion meter tmem stations over periods ranging from 2 to 6 years there were seven study areas in eastern canada the platforms were surveyed and a schmidt rock test hammer was used to measure rock hardness more than 1200 rock samples from three of the study areas were also subjected each day over a 3 year period to two tidal cycles of immersion and exposure which simulated the central intertidal zone a further 840 samples were subjected to longer periods of exposure and immersion over a 1 year period which represented different elevations within the upper and lower intertidal zone respectively these experiments suggested that tidally generated weathering and debris removal is an effective erosional mechanism particularly at the elevation of the lowest high tides in the field mean rates of downwearing for each study area ranged from 0 24 mm yr 1 to more than 1 5 mm yr 1 rates tended to increase with elevation in the field with maxima in the upper intertidal zone this trend in the field cannot be attributed entirely to the tidally induced weathering processes that were simulated in the laboratory and must reflect in part the effect of waves frost ice and other mechanisms it is concluded that there are no strong spatial downwearing patterns on shore platforms and that downwearing rates in the intertidal zone are the result of a number of erosional mechanisms with different elevation efficacy characteristics furthermore even if only one or two mechanisms were dominant in an area any resulting relationship between downwearing rates and elevation would be obscured or eliminated by the effect of variations in the chemical and physical characteristics of the rocks copyright 2010 john wiley sons ltd