effects of earthquake induced landslides on sediment budget and transport over a 50 yr period landsliding during a magnitude 7 7 earthquake in 1929 in northwestern south island new zealand delivered up to 400 000 m 3 km 2 of sediment to stream channels first to third order channels were buried to depths of as much as 10 m with sedimentary rock debris for distances ranging from 2 of the 92 km 2 study area because of the coarse grain size of the sedimentary rock debris and trapping of sediment in numerous landslide dammed lakes sand and pebble sized debris originating from landslides on a 6 6 km 2 area of granite has been transported downstream no more than 10 km at least 50 to 75 of this granitic debris is retained in the fourth order 92 km 2 catchment 50 yr after the earthquake the long retention times of sediment and the volume of debris supplied by landslides during a large earthquake suggest that earthquake induced landsliding is the principal sediment supply mechanism in the region

sediment characteristics of an extreme flood 1993 upper mississippi river valley the 1993 mississippi river flood was notable for its high magnitude long duration summer occurrence and low sediment discharge a field survey of a 70 km long reach in the vicinity of quincy illinois revealed that the event was characterized by 100 yr flood had remarkably little sedimentological or geomorphological impact on the flood plain within the study reach because the transport effectiveness of floods in large drainage basins is influenced by event sequencing in the same manner as floods in small watersheds and the cohesive flood plain soils were not susceptible to erosion

empirical master equations part ii application to stratospheric qbo solar cycle and northern annular mode abstract time series of stratospheric climate variables are used to derive master equations in the discretized phase space spanned by three variables the empirical master equation eme predicts the probability density function pdf in this phase space the numerical properties of emes have been investigated in the first part of this paper using synthetic time series in this part of the paper the time series consist of normalized and deseasonalized daily and zonally averaged meteorologically relevant quantities obtained from the 40 yr ecmwf re analysis era 40 and observations one eme reproduces the climatological features of the quasi biennial oscillation qbo of stratospheric equatorial zonal wind including the probabilistic character of transitions between phases also the arctic stratosphere at 10 hpa is about 2 k warmer during the easterly phase of the qbo than during the westerly phase another eme including a time series of the solar radio flux at 10 7 cm hints that the relationship between

microstructure and porosity evolution during experimental carbonation of a natural peridotite abstract carbonation experiments t 100 200 c pco2 14 6 19 4 mpa were performed under closed system conditions on a natural peridotite from almklovdalen w norway to investigate the microstructure and porosity evolution as a function of reaction progress the unreacted samples cubes of 2 5 3 cm3 were composed mainly of forsteritic olivine 80 90 vol clinochlore orthopyroxene amphibole and chromite initial porosities were on the order of 6 8 due to the presence of abundant inter and intragranular microfractures microstructural observations after 7 42 days of experimental treatment showed that olivine was by far the most reactive phase after 7 days at 100 c no carbonate products were formed but longer reaction times produced small amounts of magnesite on the surface and within the fracture network of the peridotite cubes increasing temperatures led to faster reactions and pore space filling by magnesite in addition replacement rims up to 50 m thick composed of magnesite and amorphous silica formed around individual olivine grains the replacement began with the formation of an amorphous silica layer that retained the shapes of the initial olivine grains this layer remained permeable during the reaction as it allowed further dissolution of the underlying olivine increasing extents of carbonation were accompanied by decreasing porosities and enhanced cementation of grain boundaries about 50 of the initial porosity was closed when carbonation reached about 10 the reacted samples showed no evidence of reaction induced cracking indicating that the carbonation reaction was self limiting in our experiments these results may have important implications for the efficiency of in situ co2 sequestration in peridotites

are segmented fracture zones weak analytical and numerical models constrain anomalous bathymetry at the clarion and murray fracture zones abstract between 150 w and 135 w the clarion fracture zone fz coalesces from six discrete fz traces to a single fz over a period of 30 million years coinciding with a change in plate motion that placed the associated transform fault tf in compression between 160 and 157 the murray fz is also comprised of several closely spaced

prolonged impact of earthquake induced landslides on sediment yield in a mountain watershed the tanzawa region japan abstract to determine for how long a landslide affects sediment discharge the sediment yields of 15 check dam basins were compared with the time series of landslide distributions in a mountain basin in the tanzawa region central japan the distribution of sediment yield was quantitatively estimated from deposition in the sediment pools of check dams the relationship between the landslide history and sediment discharge in the nakagawa river basin was examined for an approximately 80 year period two major landslide events occurred during this period the 1923 kanto earthquake and the 1972 disaster caused by heavy rainfall the resulting trend in sediment discharge of the whole basin estimated using reservoir sedimentation in the miho dam at its base was nearly constant with high sediment discharge 2897 m 3 km 2 yr 1 in the intervening quarter century despite the recovery of vegetation on landslide areas in this period comparisons of the landslide distributions resulting from the two disasters the sediment yields of check dam basins and the sediment discharge of the whole basin indicate that recent sediment discharge contains landslide debris that was originated by the kanto earthquake that occurred over 80 years ago thus to understand high sediment discharge it is essential to investigate not only the current basin condition and recent events but also the landslide history of the basin for at least the previous 100 years

evoluton of polygonal fracture patterns in lava flows cooling induced fractures also known as columnar joints divide basaltic lava flows into prismatic columns with polygonal cross sections the regularity and symmetry of the fracture patterns have long fascinated naturalists in view of the recent selection of two candidate nuclear waste sites in areas where polygonally fractured volcanic rocks are located a better understanding of the fracture patterns is required field data indicate that the tetragonal networks at flow surfaces evolve systematically to hexagonal networks as the joints grow inward during solidification of lava this evolution occurs by the gradual change of most orthogonal intersections to nonorthogonal intersections of about 120 degrees the surface features and intersection geometries of columnar joints show that joint segments at any given level form sequentially yet harmoniously

hydroclimatological and geomorphic controls on the timing and spatial variability of floods in new england usa abstract numerous methods exist to express a region s flood regime but because of the various controls on flooding no salient method emerges we have used directional also known as orientation statistics to express some of the hydroclimatological and geomorphic controls on flooding in new england and mapped these statistics for 36 gages to reveal the regional groupings of similarly responding basins directional statistics express the temporal variance of flood timings and characterize the seasonality of floods and thus begin to demonstrate some of the climatic controls on flood timing and their spatial effects contour maps of the vector mean timing of floods indicate the strong control of coastal influences on the hydrologic regime and multiple regression analyses indicate that both the surrogate variables for climate latitude and distance to the coast strongly explain the timing of the vector mean although both the geomorphic variables basin size and altitude are also significant explanatory variables an autumnal flood season exists along coastal locations but disappears moving both inland and northward through the region for many of these coastal locations especially in the south the autumn mode reflects the occurrence of hurricane induced floods which for many basins represent the largest flood in the annual series the strength of the seasonality as expressed by the mean resultant magnitude is controlled primarily by basin size with distance to the coast and altitude also important finally these results suggest that directional statistics are an appropriate method for depicting regional hydrologic regimes and in describing some of the hydroclimatological controls on flood occurrence

solution to the volume problem in serpentinization kernel pattern consists of a rim of completely serpentinized peridotite surrounding a core of partly serpentinized or unserpentinized peridotite it is found adjacent to shear zones in some serpentinites kernels are commonly rectangular with length width ratios of 1 to 3 the boundary between the completely serpentinized rim and the unserpentinized core is commonly cut at a high angle by cross fractures the cross fractures which contain either picrolite or chrysotile asbestos taper out in the core and widen in the rim they are almost always perpendicular to the core rim boundary and point into the core of the kernel in this sense they are radially distributed in the rim the kernel pattern can be observed in thin section in outcrop and on the megascopic scale of tens of metres cross fractures represent expansion fractures in serpentinite in the rim of the kernel caused by an increase in volume acompanying serpentinization of the peridotite in the core of the kernel as the serpentinization front penetrates into the kernel the serpentinized peridotite expands however the serpentinite in the rim cannot expand and must fracture to accommodate the increase in volume as serpentinization proceeds more expansion occurs extending the fractures farther into the core and requiring the fractures in the existing serpentinite to widen these fractures are subsequently filled by serpentine minerals the resulting pattern consists of a rim of serpentinite cut by serpentine veins that surrounds a core of peridotite measured densities of cross fractures in the rims of kernels are consistent with those expected from the magnitude of the volume change accompanying serpentinization of peridotite

in situ carbonation of peridotite for co2 storage the rate of natural carbonation of tectonically exposed mantle peridotite during weathering and low temperature alteration can be enhanced to develop a significant sink for atmospheric co2 natural carbonation of peridotite in the samail ophiolite an uplifted slice of oceanic crust and upper mantle in the sultanate of oman is surprisingly rapid carbonate veins in mantle peridotite in oman have an average 14c age of 26 000 years and are not 30 95 million years old as previously believed these data and reconnaissance mapping show that 104 to 105 tons per year of atmospheric co2 are converted to solid carbonate minerals via peridotite weathering in oman peridotite carbonation can be accelerated via drilling hydraulic fracture input of purified co2 at elevated pressure and in particular increased temperature at depth after an initial heating step co2 pumped at 25 or 30 c can be heated by exothermic carbonation reactions that sustain high temperature and rapid reaction rates at depth with little expenditure of energy in situ carbonation of peridotite could consume 1 billion tons of co2 per year in oman alone affording a low cost safe and permanent method to capture and store atmospheric co2

intense fracturing and fracture sealing induced by mineral growth in porous rocks article i nfo mineral precipitation in the pores of a rock may exert a force which is called crystallization pressure this process has been studied experimentally and results bring a new look on the way fractures may develop and seal in natural systems cylindrical core samples of porous limestone and sandstone were left for several weeks in contact with an aqueous solution saturated with sodium chloride at 30 or 45 c under axial normal stress in the range 0 02 0 26 mpa the fluid was allowed to rise in the core samples by capillary forces up to a controlled height where evaporation and precipitation occurred the uniaxial deformation of the samples was measured using high resolution displacement sensors the samples were characterized using computed x ray tomography allowing therefore imaging in 3d the intensity and localization of the damage two kinds of damage could be observed firstly small rock fragments were peeled from the sample surface secondly

impact of reach geometry on stream channel sensitivity to extreme floods predicting spatial and temporal variations in bank erosion due to extreme floods presents a long standing challenge in geomorphology we develop two methodologies for rapid regional scale assessments of stream reaches susceptible to channel widening the first proposes that channel widening occurs when unit stream power exceeds a critical threshold 300 w m2 the second is motivated by the observation that widening often occurs at channel bends we introduce a new metric the bend stress parameter which is proportional to the centripetal force exerted on a concave bank we propose that high centripetal forces generate locally high bank shear forces and enhance channel bank erosion we test both metrics using the geomorphic signature of tropical storm irene 2011 on the white and the saxtons rivers vermont specifically we test if reaches where significant channel widening occurred during irene required one or both metrics to exceed threshold values we observe two distinct styles of channel widening where unit stream power and bend stress parameter are high widening is usually due to bank retreat elsewhere widening is usually due to the stripping of the upstream end of mid channel islands excluding widening associated with the stripping of the heads of mid channel islands almost all the widening 98 occurred along reaches identified as susceptible to widening the combined metrics identify up to one quarter of the reaches lacking susceptibility to channel widening copyright 2014 john wiley sons ltd

dissolution assisted pattern formation during olivine carbonation olivine and pyroxene bearing rocks in the oceanic crust react with hydrothermal fluids producing changes in the physical characteristics and behaviors of the altered rocks notably these reactions tend to increase solid volume reducing pore volume permeability and available reactive surface area yet entirely hydrated and or carbonated rocks are commonly observed in the field we investigate the evolution of porosity and permeability of fractured dunites reacted with co2 rich solutions in laboratory experiments the alteration of crack surfaces changes the mechanical and transport properties of the bulk samples analysis of three dimensional microstructural data shows that although precipitation of secondary minerals causes the total porosity of the sample to decrease an interconnected network of porosity is maintained through channelized dissolution and coupled carbonate precipitation the observed microstructure appears to be the result of chemo mechanical coupling which may provide a mechanism of porosity maintenance without the need to invoke reaction driven cracking

nonlinear dynamics of ice wedge networks and resulting sensitivity to severe cooling events patterns of subsurface wedges of ice that form along cooling induced tension fractures expressed at the ground surface by ridges or troughs spaced 10 30 m apart are ubiquitous in polar lowlands1 fossilized ice wedges which are widespread at lower latitudes have been used to infer the duration2 3 4 and mean temperature5 6 of cold periods within proterozoic2 and quaternary climates3 4 5 6 7 8 9 10 11 12 13 and recent climate trends have been inferred from fracture frequency in active ice wedges14 here we present simulations from a numerical model for the evolution of ice wedge networks over a range of climate scenarios based on the interactions between thermal tensile stress fracture and ice wedges we find that short lived periods of severe cooling permanently alter the spacing between ice wedges as well as their fracture frequency this affects the rate at which the widths of ice wedges increase as well as the network s response to subsequent climate change we conclude that wedge spacing and width in ice wedge networks mainly reflect infrequent episodes of rapidly falling ground temperatures rather than mean conditions

experimental evidence of reaction induced fracturing during olivine carbonation author s zhu w fusseis f lisabeth h xing t xiao x de andrade v karato si abstract 2016 american geophysical union all rights reserved mineral carbonation a process that binds co2 in the form of carbonates by silicate weathering is widespread on the earth s surface because of the abundance of silicate rocks and the permanence of the carbonated solids sequestering co2 via mineral carbonation has generated lots of interests however it is unclear how the fluid rock reaction proceeds to completion in spite of an increasing solid volume we conducted a mineral carbonation experiment in which a sintered olivine aggregate reacted with a sodium bicarbonate solution at reservoir conditions time resolved synchrotron x ray microtomographic images show cracks in polygonal patterns arising in the surface layers and propagating into the interior of the olivine aggregate the nanotomography data reveal that the incipient cracks intersect at right angles we infer that stretching due to nonuniform volume expansion generates polygonal cracking of the surfaces our data shed new lights on the processes that control hydration and carbonation of peridotite

suspended sediment load during floods in a small stream of the dolomites northeastern italy abstract suspended sediment load was analyzed in a small high gradient stream of the eastern italian alps which was instrumented to measure discharge and sediment transport the ratio of suspended to total sediment yield and the relations between sediment concentration and water discharge were analyzed for seven floods which occurred from 1991 to 1996 in summer and autumn from june to october different patterns of hysteresis in the relation between suspended sediment and discharge were related to types and locations of active sediment sources the within storm variation of particle size of suspended sediment during a major flood indicates a coarsening of transported material for increasing discharge an analysis of grain size has shown that erosion areas on hillslopes were the main sources of suspended load

sediment transport due to extreme events the hudson river estuary after tropical storms irene and lee 1 tropical storms irene and lee in 2011 produced intense precipitation and flooding in the u s northeast including the hudson river watershed sediment input to the hudson river was approximately 2 7 megaton about 5 times the long term annual average rather than the common assumption that sediment is predominantly trapped in the estuary observations and model results indicate that approximately two thirds of the new sediment remained trapped in the tidal freshwater river more than 1 month after the storms and only about one fifth of the new sediment reached the saline estuary high sediment concentrations were observed in the estuary but the model results suggest that this was predominantly due to remobilization of bed sediment spatially localized deposits of new and remobilized sediment were consistent with longer term depositional records the results indicate that tidal rivers can intercept at least temporarily delivery of terrigenous sediment to the marine environment during major flow events

source conveyance and fate of suspended sediments following hurricane irene new england usa hurricane irene passed directly over the connecticut river valley in late august 2011 intense precipitation and high antecedent soil moisture resulted in record flooding mass wasting and fluvial erosion allowing for observations of how these rare but significant extreme events affect a landscape still responding to pleistocene glaciation and associated sediment emplacement clays and silts from upland glacial deposits once suspended in the stream network were routed directly to the mouth of the connecticut river resulting in record breaking sediment loads fifteen times greater than predicted from the pre existing rating curve denudation was particularly extensive in mountainous areas we calculate that sediment yield during the event from the deerfield river a steep tributary comprising 5 of the entire connecticut river watershed exceeded at minimum 10 40 years of routine sediment discharge and accounted for approximately 40 of the total event sediment discharge from the connecticut river a seriesof surface sediment corestaken in floodplainponds adjacent to the tidalsec

experimental evidence for chemo mechanical coupling during carbon mineralization in ultramafic rocks abstract storing carbon dioxide in the subsurface as carbonate minerals has the benefit of long term stability and immobility ultramafic rock formations have been suggested as a potential reservoir for this type of storage due to the availability of cations to react with dissolved carbon dioxide and the fast reaction rates associated with minerals common in ultramafic formations however the rapid reactions have the potential to couple with the mechanical and hydraulic behavior of the rocks and little is known about the extent and mechanisms of this coupling in this study we argue that the dissolution of primary minerals and the precipitation of secondary minerals along pre existing fractures in samples lead to reductions in both the apparent young s modulus and shear strength of aggregates accompanied by reduction in permeability hydrostatic and triaxial deformation experiments were run on dunite samples saturated with de ionized water and carbon dioxide rich solutions while stress strain permeability and pore fluid chemistry were monitored sample microstructures were examined after reaction and deformation using scanning electron microscopy sem the results show that channelized dissolution and carbonate mineral precipitation in the samples saturated with carbon dioxide rich solutions modify the structure of grain boundaries leading to the observed reductions in stiffness strength and permeability a geochemical model was run to help interpret fluid chemical data and we find that the apparent reaction rates in our experiments are faster than rates calculated from powder reactors suggesting mechanically enhanced reaction rates in conclusion we find that chemo mechanical coupling during carbon mineralization in dunites leads to substantial modification of mechanical and hydraulic behavior that needs to be accounted for in future modeling efforts of in situ carbon mineralization projects

forsterite dissolution and magnesite precipitation at conditions relevant for deep saline aquifer storage and sequestration of carbon dioxide the products of forsterite dissolution and the conditions favorable for magnesite precipitation have been investigated in experiments conducted at temperature and pressure conditions relevant to geologic carbon sequestration in deep saline aquifers although forsterite is not a common mineral in deep saline aquifers the experiments offer insights into the effects of relevant temperatures and pco2 levels on silicate mineral dissolution and subsequent carbonate precipitation mineral suspensions and aqueous solutions were reacted at 30 c and 95 c in batch reactors and at each temperature experiments were conducted with headspaces containing fixed pco2 values of 1 and 100 bar reaction products and progress were determined by elemental analysis of the dissolved phase geochemical modeling and analysis of the solid phase using scanning electron microscopy infrared spectroscopy and x ray diffraction the extent of forsterite dissolution increased with both increasing temperature and pco2 the release of mg and si from forsterite was stoichiometric but the si concentration was ultimately controlled by the solubility of amorphous silica during forsterite dissolution initiated in deionized water the aqueous solution reached supersaturated conditions with respect to magnesite however magnesite precipitation was not observed for reaction times of nearly four weeks magnesite precipitation was observed in a series of experiments with initial solution compositions that simulated extensive forsterite dissolution the precipitation of magnesite appears to be limited by the process of nucleation and nucleation requires a critical saturation index between 0 25 and 1 14 at 95 c and 100 bar pco2 magnesite precipitation is fastest in the presence of an initial magnesite seed although magnesite precipitates do form on the surfaces of forsterite particles the presence of the forsterite surface does not significantly accelerate magnesite precipitation relative to solid free systems

changes in land cover and shallow landslide activity a case study in the spanish pyrenees the pyrenees like many other mountain areas in europe have experienced depopulation and land abandonment during the 20th century this has encouraged vegetation recovery in formerly occupied areas including reforestation to promote woodland the objective of this study is to analyse the effects of these changes on shallow landsliding a process responsible for erosion and land degradation in many mountain areas a sequence of aerial images reveals a slight decrease in the landslide occurrence rate in the last half of the 20th century and a parallel increase in the landslide extinction rate i e the rate at which evidence of landslide activity is removed by vegetation colonisation a logistic regression routine was used to assess the influence of land use and vegetation recovery in the occurrence of shallow landslides the result shows that the former arable fields on the valley slopes still facilitate landsliding even after land abandonment and revegetation by shrubs or trees a shift in the topographic location of landslides was also detected pointing to an increased importance of water redistribution in the slopes after prolonged rainfall periods

permeability profiles across the crust mantle sections in the oman drilling project inferred from dry and wet resistivity data permeability profiles in the crust mantle sequences of the samail ophiolite were constructed based on onboard measurements of the electrical resistivity of cores recovered during the oman drilling project for each sample we measured dry and brine saturated resistivity during the description campaign on the drilling vessel chikyu owing to the conductive brine in the pore space wet resistivity is systematically lower than dry resistivity the difference between dry and wet resistivity is attributed to the movement of dissolved ions in brine that occupies the pore space we applied effective medium theory to calculate the volume fraction of pores that contribute to electrical transport using an empirical cubic law between transport porosity and permeability we constructed permeability profiles for the crust mantle transition zone and the serpentinized mantle sections in the samail ophiolite the results indicate that 1 the gabbro sequence has a markedly lower permeability than the underlying mantle sequence 2 serpentinized dunites have higher permeability than serpentinized harzburgites and 3 discrete sample permeability is correlated with ultrasonic velocity suggesting that the permeability variations predominately reflect crack density and geometry

microscale characterization of rupture nucleation unravels precursors to faulting in rocks abstract precursory signals manifestations of microscale damage that precedes dynamic faulting are key to earthquake forecasting and risk mitigation detections of precursors have primarily relied on measurements performed using sensors installed at some distance away from the rupture area in both field and laboratory experiments direct observations of continuous microscale damage accumulated during fault nucleation and propagation are scarce using an x ray transparent triaxial deformation apparatus we show the first quantitative high resolution three dimensional 3d information about damage evolution of rocks undergoing brittle failure the dynamic microtomography images documented a spectrum of damage characteristics and different fault growth patterns the interplay between various deformation mechanisms can result in either a positive negative or constant net volume change consequently changes in rock density and acoustic wave velocities before faulting are expected to vary in different tectonics settings hence making failure forecasting intrinsically dependent on rock type at depth

modeling the impact of nano pores on mineralization in sedimentary rocks 1 by limiting crystal size nanometer scale pores in geological media can control the effective solubility of mineral phases since mineralization is determined by solubility this mechanism termed pore size controlled solubility pcs is potentially significant for the evolution of porosity and permeability during reactive transport to demonstrate the potential impact in geological systems we developed a new one dimensional numerical model using a moving boundary condition to describe the mineralization in the rock matrix adjacent to a pressure solution stylolite interface in the model the porous domain initially possesses a polymodal pore size distribution although this is allowed to change in response to mineral precipitation and the evolution of porosity and pore size distributions was simulated both for systems with constant mineral solubility and for systems in which solubility was pore size controlled consistent with field observations total porosity decreases near the stylolite interface in all the simulations however in systems with constant solubility nanometer scale pores close rapidly because of their high specific surface area by contrast when the pcs mechanism is included in the model transient bimodal pore size distributions develop with nano pores remaining open throughout the simulation our simulations suggest that the combination of the pcs mechanism with kinetic models for mineral precipitation can account for the bimodal pore size distributions observed in sedimentary carbonate rocks furthermore while the mechanism is unlikely to affect rocks such as sandstones pcs can impact carbonate and clay bearing sediments which typically possess high levels of submicron porosity

reaction assisted hierarchical fracturing during serpentinization abstract hierarchical fracture patterns are the result of a fracturing process that successively divides rocks into smaller domains in a 2d outcrop section such fracture patterns are characterized by four sided domains and t junctions where new fractures stop growing at right angles to pre existing fractures here we describe fracturing of mm to dm thick serpentinized orthopyroxenite dykes in a dunite matrix from the leka ophiolite complex in nord trondelag norway the fracturing process is driven by volume changes associated with the serpentinization of the dunites during this process the orthopyroxenite dykes are extended by the expanding dunite and undergo considerable fracturing the resulting fracture patterns are hierarchical the cumulative distributions of fracture lengths show a scaling behavior that lies between a log normal and power law fractal distribution this is consistent with a simple fragmentation model in which domains are divided according to a top hat distribution of new fracture positions within unfractured domains reaction assisted hierarchical fracturing is also likely to be responsible for other structures commonly observed in serpentinized ultramafic rocks including the mesh textures observed in individual olivine grains and the high abundance of rectangular domains at a wide range of scales this mechanism may provide first order controls on fluid migration rates in a wide variety of geological settings

olivine dissolution and carbonation under conditions relevant for in situ carbon storage abstract in order to evaluate the chemistry and kinetics of mineral carbonation reactions under conditions relevant to subsurface injection and storage of co 2 olivine alteration was studied at 60 c and 100 bar co 2 pressure including olivine dissolution and the formation of carbonate minerals batch experiments were performed with olivine fo92 water co 2 and nacl inside gold cells contained within rocking autoclaves two reproducible experiments yielded an initial 1 h dissolution rate of 9 50 0 10 10 11 and a long term 10 70 days rate of 1 69 0 23 10 12 mol cm 2 s 1 the long term rate is consistent with previously published rate laws at 4 5 2 aq and sio 2 aq at 60 c a si rich surface layer forms on olivine grains within 2 days of reaction and appears to slow dissolution by passivating the surface the olivine dissolution rate decreases by 2 orders of magnitude over 4 days as the system approaches amorphous silica saturation but remains constant thereafter based on a linear increase in mg concentrations secondary phases consist of amorphous silica and magnesite with up to 7 mol olivine converted to mg carbonate over 94 days of reaction magnesite precipitation rates could not be precisely quantified due to experimental limitations however our minimum estimate of 1 40 10 13 mol cm 2 s 1 suggests that the precipitation rate is several orders of magnitude greater than predicted by previous studies finally the presence of 0 5 m nacl resulted in a decrease in olivine dissolution rate at reaction times of less than 4 days but a significant enhancement of the reaction rate at reaction times greater than 4 days relative to electrolyte free experiments our results suggest that geochemical models developed to predict the behavior of subsurface co 2 storage systems in mafic and ultramafic rocks should incorporate the effects of dissolved species including sio 2 and nacl

the geomorphic function and characteristics of large woody debris in low gradient rivers coastal maine usa abstract the role function and importance of large woody debris lwd in rivers depend strongly on environmental context and land use history the coastal watersheds of central and northern maine northeastern u s are characterized by low gradients moderate topography and minimal influence of mass wasting processes along with a history of intensive commercial timber harvest in spite of the ecological importance of these rivers which contain the last wild populations of atlantic salmon salmo salar in the u s we know little about lwd distribution dynamics and function in these systems we conducted a cross basin analysis in seven coastal maine watersheds documenting the size frequency volume position and orientation of lwd as well as the association between lwd pool formation and sediment storage in conjunction with these lwd surveys we conducted extensive riparian vegetation surveys we observed very low lwd frequencies and volumes across the 60 km of rivers surveyed frequency of lwd 20 cm diameter ranged from 15 50 pieces km 1 and wood volumes were commonly 3 km 1 moreover most of this wood was located in the immediate low flow channel zone was oriented parallel to flow and failed to span the stream channel as a result pool formation associated with lwd is generally lacking and

olivine dissolution rates a critical review abstract the dissolution rates of olivine have been considered by a plethora of studies in part due to its potential to aid in carbon storage and the ease in obtaining pure samples for laboratory experiments due to the relative simplicity of its dissolution mechanism most of these studies provide mutually consistent results such that a comparison of their rates can provide insight into the reactivity of silicate minerals as a whole olivine dissolution is controlled by the breaking of octahedral m2 oxygen bonds at or near the surface liberating adjoining sio44 tetrahedra to the aqueous fluid aqueous species that adsorb to these bonds apparently accelerate their destruction for example the absorption of h h2o and at some conditions selected aqueous organic species will increase olivine dissolution rates nevertheless other factors can slow olivine dissolution rates notably olivine dissolution rates are slowed by lowering the surface area exposed to the reactive aqueous fluid by for example the presence and or growth on these surfaces of either microbes or secondary phases the degree to which secondary phases decelerate rates depends on their ability to limit access of the reactive aqueous fluids to the olivine surface it seems likely that these surface area limiting processes are very significant in natural systems lowering olivine surface reactivity in many environments compared to rates measured on cleaned surfaces in the laboratory a survey of the literature suggests that the major factors influencing forsteritic olivine dissolution rates are 1 ph 2 water activity 3 temperature and 4 mineral fluid interfacial surface area evidence suggests that the effects of aqueous inorganic and organic species are relatively limited and may be attributed at least in part to their influence on aqueous solution ph moreover the observed decrease in rates due to the presence of secondary mineral coatings and or the presence of microbes can be attributed to their ability to decrease olivine surface area directly exposed to the reactive aqueous fluid as the reactivity of forsterite surfaces are spatially heterogeneous its surface area normalized rates will tend to decrease as it dissolves even in the absence of a mineral or bacterial coating each of these factors limits and or influences the application of forsterite dissolution to 1 enhanced weathering efforts 2 mineral carbonation and 3 the low temperature generation of hydrogen or hydrocarbons via the oxidation of its divalent iron

three dimensional imaging of fracture propagation in tight sandstones of the upper triassic chang 7 member ordos basin northern china abstract the characteristics of fracture propagation in heterogeneous tight sandstones are critical to volumetric fracturing which is the key to unlocking unconventional resources in tight sandstones quantification of the influence of pre existing pore systems and particle arrangements on the propagation of fractures is challenging due to inadequate imaging of the internal void systems in tight sandstones from three dimensional 3d aspect in this study the 3d geometry of tight sandstones from the chang 7 member in the ordos basin is continuously imaged under different loading stresses and the voxel resolution of the x ray computed tomography is 2 5 m the data set captured in this process shows the changes in the samples at the microstructural level as they approach fracturing the data are stored as a time series of 3d images the results demonstrate that i fractures propagate progressively and gradually link with pre existing pores resulting in macroscopic fractures with a maximum width of 250 m while newly generated fractures could break up particles and may not follow the line of pre existing fractures and ii three stages were identified in the failure process of tight sandstones with new fractures running at an angle of about 30 to the general direction of the stress of compression the total volumes of both the sample and pore fractures and the damage index which were extracted from the 3d images all increased when approaching fracturing the final volume of pore fracture systems could be 11 times that of the initial pore volume all of these observations provide valuable insights and design guidelines for hydraulic fracturing in unconventional tight sandstones and a quantified model of the dynamics and the morphology of fracture propagation with increasing stress approaching failure which may shed light on dynamic critical transitions in the earth s crust

bedload entrainment in low gradient paraglacial coastal rivers of maine u s a implications for habitat restoration abstract the rivers of coastal maine flow through mainstem lakes and long low gradient reaches that break the continuum of bedload transport expected in nonparaglacial landscapes stream erosion of glacial deposits supplies coarse sediment to these systems the land use history includes intensive timber harvest and associated dam construction which may have altered the frequency of substrate mobilizing events these watersheds are vital habitat for the last remaining wild anadromous atlantic salmon in the united states future adjustments in channel morphology and habitat quality via natural stream processes or restoration projects depend on erosion transport and deposition of coarse sediment these factors motivate our study of competence at four sites in the sheepscot and narraguagus watersheds three of the four sites behaved roughly similarly with particle entrainment during intervals that include winter ice and spring flood conditions and relatively minor bed mobilization during moderate floods in the summer and fall with a recurrence interval of 2 3 years the fourth site on the sheepscot river mainstem exhibits more vigorous entrainment of marked particles and more complex three dimensional channel morphology this contrast is partially due to local geomorphic conditions that favor high shear stresses particularly relatively steep gradient but also likely to nourishment of the bedload saltation system by recruitment from an eroding glacial deposit upstream our results suggest that the frequency and magnitude of bedload transport are reach specific depending on factors including local channel geometry upstream sediment supply and transport and formation of anchor ice this presents a challenge for stream practitioners in this region different reaches may require contrasting management strategies our results underscore the importance of understanding channel processes at a given site and assessing conditions upstream and downstream as a prerequisite for conducting habitat restoration projects

rate of serpentinization in seafloor environments the permeability of partially serpentinized peridotites has been measured near room temperature and found to be in the range of 10 11 to 10 12 darcys or 10 7 to 10 8 cm2 sec 1 comparable to shaley materials serpentinites act as semipermeable membranes to salt ions in ocean crust and deep groundwater environments serpentinization must be a continuous process controlled only by water access to ultramafic rocks through their cover given this it will generate high local strains and stresses with episodic cracking the serpentinization process may also contribute to heat flow and ocean floor topography

self organization of sorted patterned ground striking circular labyrinthine polygonal and striped patterns of stones and soil self organize in many polar and high alpine environments these forms emerge because freeze thaw cycles drive an interplay between two feedback mechanisms first formation of ice lenses in freezing soil sorts stones and soil by displacing soil toward soil rich domains and stones toward stone rich domains second stones are transported along the axis of elongate stone domains which are squeezed and confined as freezing soil domains expand in a numerical model implementing these feedbacks circles labyrinths and islands form when sorting dominates polygonal networks form when stone domain squeezing and confinement dominate and stripes form as hillslope gradient is increased

differentiating the relative importance of land cover change and geomorphic processes on fine sediment sequestration in a logged watershed abstract timber harvest often results in accelerated soil erosion and subsequent elevated fine

earthquake triggered increase in sediment delivery from an active mountain belt in tectonically active mountain belts earthquake triggered landslides deliver large amounts of sediment to rivers we quantify the geomorphic impact of the 1999 mw 7 6 chi chi earthquake in taiwan which triggered 20 000 landslides coseismic weakening of substrate material caused increased landsliding during subsequent typhoons most coseismic landslides remained confined to hillslopes downslope transport of sediment into the channel network occurred during later storms the sequential processes have led to a factor of four increase in unit sediment concentration in rivers draining the epicentral area and increased the magnitude and frequency of hyperpycnal sediment delivery to the ocean four years after the earthquake rates of hillslope mass wasting remain elevated in the epicentral area

reaction fronts permeability and fluid pressure development during dehydration reactions abstract fluids released by prograde metamorphism are often invoked to explain a range of crustal processes from earthquake triggering to metasomatism these fluids can be either trapped and overpressured or released and channelized depending on the interplay between permeability reaction rate and compaction experimental data are presented measuring permeability porosity and microstructural evolution throughout the dehydration of gypsum to form bassanite reaction fronts regions over which the reaction largely occurs are used as a framework to explain the results experiments were conducted under hydrostatic conditions at a constant temperature of 115 c at two effective pressures of 60 mpa and 110 mpa and three pore fluid pressures of 20 40 and 60 mpa at high effective pressure creep of the gypsum solid framework results in low porosity and permeability producing high pore fluid pressure build up that slows the reaction rate a clearly defined narrow reaction front migrates along the sample and the average permeability remains low until the front sweeps across the entire sample conversely at low effective pressure the reaction front is wide producing a permeable drained network average permeability is enhanced significantly after only a small fraction of the reaction has completed by the interconnection of open pores this study shows that the width of reaction fronts and hence the permeability development is strongly controlled by compaction the reaction front velocity is broadly dependent on permeability and the reaction driving force a simple quantitative model for these relationships is developed

the efficacy of stream power and flow duration on geomorphic responses to catastrophic flooding abstract geomorphologists have long studied the impacts of extreme floods yet the association between the magnitude of flow parameters discharge velocity shear stress or stream power and resulting geomorphic effectiveness remains vague and non deterministic attempts have been made to include flow duration and total expenditure of stream power in combination with peak unit stream power as important variables but there has been minimal exploration of this hydraulic combination taking advantage of tropical storm irene s rapid track through eastern vermont usa in late summer 2011 this paper presents the array of geomorphic responses to a short duration time to peak of