dating the subduction of the arabian continental margin beneath the semail ophiolite oman the presence of high pressure p eclogites along the northeast margin of the arabian continental plate beneath the semail ophiolite demonstrates that subduction of thinned continental crust to pressures of 20 kbar 80 km depth has occurred current debate centers on whether this high p metamorphism occurred prior to during or following ophiolite emplacement which is known to have started ca 95 93 ma five concordant u pb zircon ages from a garnet clinopyroxene phengite crossite eclogite from as sifah northeast oman precisely constrain the age of high p metamorphism at 79 1 0 3 ma this age demonstrates that high p metamorphism occurred during continental subduction 15 m y after formation of the ocean floor that subsequently became the semail ophiolite

microseismicity of the bearn range reactivation of inversion and collision structures at the northern edge of the iberian plate the bearn range located to the north of the axial zone in the western pyrenees is affected by numerous small magnitude seismic events these events overlap an area characterised by specific geological structures which are interpreted to have resulted from multistage extensional and compressional deformation an analysis of surface geology draped over dem together with field investigations allow identification of two main shortening episodes with differing direction of contraction d1 represents the inversion of the north pyrenean basin whose mesozoic infill was detached from highly extended crust and transported southwards over the necking zone and the northern margin of the iberian plate d2 corresponds to the collision stage and is characterised in the study area by backfolding and backthrusting deformation coeval with uplift in the axial part of the chain due to thickening of the iberian plate the microseismicity appears to concentrate along the basal part of the inverted basin units d1 where this initially low angle thrust has been tilted and steepened during collision d2 we propose that local steepening of this ancient inversion structure which should not be named north pyrenean fault provided the suitable dip for extensional solicitation in association with the present uplift of the axial zone whatever the driving mechanism of this uplift could be

tropical cyclone driven erosion of the terrestrial biosphere from mountains the transfer of organic carbon from the terrestrial biosphere to the oceans via erosion and riverine transport constitutes an important component of the global carbon cycle measurements of particulate organic carbon load and composition in the liwu river taiwan during cyclone triggered floods suggest that tropical cyclones may facilitate the delivery of non fossil particulate organic carbon to the ocean and its subsequent burial the transfer of organic carbon from the terrestrial biosphere to the oceans via erosion and riverine transport constitutes an important component of the global carbon cycle1 2 3 4 more than one third of this organic carbon flux comes from sediment laden rivers that drain the mountains in the western pacific region3 5 this region is prone to tropical cyclones but their role in sourcing and transferring vegetation and soil is not well constrained here we measure particulate organic carbon load and composition in the liwu river taiwan during cyclone triggered floods we correct for fossil particulate organic carbon using radiocarbon and find that the concentration of particulate organic carbon from vegetation and soils is positively correlated with water discharge floods have been shown to carry large amounts of clastic sediment6 non fossil particulate organic carbon transported at the same time may be buried offshore under high rates of sediment accumulation7 8 9 we estimate that on decadal timescales 77 92 of non fossil particulate organic carbon eroded from the liwu catchment is transported during large cyclone induced floods we suggest that tropical cyclones which affect many forested mountains within the intertropical convergence zone10 may provide optimum conditions for the delivery and burial of non fossil particulate organic carbon in the ocean this carbon transfer is moderated by the frequency intensity and duration of tropical cyclones

transport of terrestrial organic carbon to the oceans by rivers re estimating flux and burial rates this study re estimates one important component in the global carbon cycle the modern global fluviatile organic carbon discharge and burial rates according to these results approximately 430 1012 g of terrestrial organic carbon are transported to the ocean in modern times this amount is higher than the latest estimates but takes into account new data from oceania not previously considered in global flux studies however only the minor amount of 10 or approximately 43 1012 gc year 1 is most likely buried in marine sediments this amount is similar to the burial of marine organic carbon in the coastal ocean 55 1012 gc year 1 adding both estimates gives approximately 100 1012 gc year 1 which is the value calculated by berner 1982 for terrestrial deltaic shelf sediments however the results in this study suggest that on a global scale the organic carbon content in coastal ocean sediments is not solely of terrestrial origin but a mixture of nearly equal amounts of marine and terrestrial organic carbon the major part of the terrestrial organic carbon that enters the ocean by rivers approximately 400 1012 gc year 1 seems to be either a remineralised in the ocean whereas the mechanism by which the terrestrial organic carbon is oxidised in the ocean are unknown or b is dispersed throughout the oceans and accumulates in pelagic sediments

quantifying rainfall controls on catchment scale landslide erosion in taiwan landslide erosion is a dominant hillslope process and the main source of stream sediment in tropical tectonically active mountain belts in this study we quantified landslide erosion triggered by 24 rainfall events from 2001 to 2009 in three mountainous watersheds in taiwan and investigated relationships between landslide erosion and rainfall variables the results show positive power law relations between landslide erosion and rainfall intensity and cumulative rainfall with scaling exponents ranging from 2 94 to 5 03 additionally landslide erosion caused by typhoon morakot is of comparable magnitude to landslide erosion caused by the chi chi earthquake mw 7 6 or 22 24 years of basin averaged erosion comparison of the three watersheds indicates that deeper landslides that mobilize soil and bedrock are triggered by long duration rainfall whereas shallow landslides are triggered by short duration rainfall these results suggest that rainfall intensity and watershed characteristics are important controls on rainfall triggered landslide erosion and that severe typhoons like high magnitude earthquakes can generate high rates of landslide erosion in taiwan copyright 2012 john wiley sons ltd

the potential impact of climate change on typhoon triggered landslides in taiwan 2010 2099 abstract in the western north pacific including taiwan typhoons tropical cyclones and rainfall rates are predicted to intensify as a result of climate change because typhoons are the major triggers of shallow landslides in taiwan landslide activity is expected to increase as global warming continues to assess the worst scenario of landslide occurrence in a mountainous watershed till the end of the century this study developed a method to select a global climate model gcm from 21 available gcms and correct its monthly precipitation data before downscaling annual maximum 24 h rainfall from the corrected gcm data as input to the factor of safety model for landslide prediction average annual maximum rainfall is expected to increase from 322 mm in 1960 2008 to 371 mm in 2010 2099 average total unstable area is expected to increase from 1135 ha in 1960 2008 to 1280 ha in 2010 2099 a 12 increase as a first attempt to assess landslide activity due to global warming this study is useful as a reference for watershed management in taiwan the results must be evaluated in light of uncertainties caused by the correction and downscaling of gcm data and the input parameters to the slope stability model

a preliminary assessment of the impact of landslide earthflow and gully erosion on soil carbon stocks in new zealand abstract in geomorphically active landscapes such as new zealand quantitative data on the relationship between erosion and soil carbon c are needed to establish the effect of erosion on past soil c stocks and future stock changes the soil c model currently used in new zealand for soil c stock reporting does not account for erosion this study developed an approach to characterise the effect of erosion suitable for soil c stock reporting and provides an initial assessment of the magnitude of the effect of erosion a series of case studies were used to establish the local effect of landslide earthflow and gully erosion on soil c stocks and to compare field measurements of soil c stocks with model estimates multitemporal erosion mapping from orthophotographs was used to characterise erosion history identify soil sampling plot locations and allow soil c stocks to be calculated accounting for erosion all eroded plots had lower soil c stocks than uneroded by mass movement and gully erosion plots sampled at the same sites landsliding reduces soil c stocks at plot and landscape scale largely as a result of individual large storms after about 70 years soil c stocks were still well below the value measured for uneroded plots by 40 for scars and 20 30 for debris tails indicating that the effect of erosion is very persistent earthflows have a small effect on estimates of baseline 1990 soil c stocks and reduce soil c stocks at landscape scale gullies have local influence on soil c stocks but because they cover a small proportion of the landscape have little influence at landscape scale at many of the sites the soil c model overestimates landscape scale soil c stocks

soil and biomass carbon re accumulation after landslide disturbances in high standing islands of the western pacific typhoon triggered landslides occasionally strip parts of the landscape of its vegetative cover and soil layer and export large amounts of biomass and soil organic carbon oc from land to the ocean after such disturbances new vegetation colonizes the landslide scars and oc starts to reaccumulate in the subtropical mountains of taiwan and in other parts of the world bamboo bambusoideae species may invade at a certain point in the succession of recovering landslide scars bamboo has a high potential for carbon sequestration because of its fast growth and dense rooting system however it is still largely unknown how these properties translate into soil oc re accumulation rates after landslide disturbance in this study a chronosequence was established on four former landslide scars in the central mountain range of taiwan ranging in age from 6 to 41 years post disturbance as determined by landslide mapping from remote sensing the younger landslide scars were colonized by miscanthus floridulus while after approx 15 to 20 years of succession bamboo species phyllostachys were dominating biomass and soil oc stocks were measured on the recovering landslide scars and compared to an undisturbed cryptomeria japonica forest stand in the area after initially slow re vegetation biomass carbon accumulated in miscanthus stands with mean annual accretion rates of 2 0 5 mg c ha 1 yr 1 biomass carbon continued to increase after bamboo invasion and reached 40 of that in the reference forest site after 41 years of landslide recovery soil oc accumulation rates were 2 0 mg c ha 1 yr 1 6 to 41 years post disturbance reaching 64 of the level in the reference forest our results from this in situ study suggest that recovering landslide scars are strong carbon sinks once an initial lag period of vegetation re establishment is overcome

landslide impact on organic carbon cycling in a temperate montane forest in humid forested mountain belts bedrock landslides can harvest organic carbon from above ground biomass and soil ocmodern while acting to refresh the landscape surface and turnover forest ecosystems here the impact of landslides on organic carbon cycling in 13 river catchments spanning the length of the western southern alps new zealand is assessed over four decades spatial and temporal landslide maps are combined with the observed distribution and measured variability of hillslope ocmodern stocks on average it is estimated that landslides mobilized 7 6 2 9 tc km 2 yr 1 of ocmodern 30 of which was delivered to river channels comparison with published estimates of ocmodern export in river suspended load suggests additional erosion of ocmodern by small shallow landslides or overland flow in catchments the exported ocmodern may contribute to geological carbon sequestration if buried in sedimentary deposits landslides may have also contributed to carbon sequestration over shorter timescales 100 years 5 4 3 0 tc km 2 yr 1 of the eroded ocmodern was retained on hillslopes representing a net carbon sink following re vegetation of scar surfaces in addition it was found that landslides caused rapid turnover of the landscape with rates of 0 3 of the surface area per decade high rates of net ecosystem productivity were measured in this forest of 94 11 tc km 2 yr 1 which is consistent with rapid landscape turnover suppressing ecosystem retrogression landslide ocmodern yields and rates of turnover vary between river catchments and appear to be controlled by gradients in climate precipitation and geomorphology rock exhumation rate topographic slope copyright 2011 john wiley sons ltd

soil properties on a chronosequence of landslides in montane rain forest ecuador to assess the impact of landslides on soil fertility in south ecuador we compared the properties of shallow translational debris slides with those of adjacent undisturbed soils a chronosequence of four small landslides ca 0 5 ca 2 3 ca 8 10 and ca 20 years old was selected on a 30 50 forest covered east facing slope of the eastern cordillera at 1900 2300 m above sea level a s l all soils were dystric cambisols the mean mass of the soil organic layer sum of all o horizons increased in the order landslide head 46 t ha 1 central part track 101 t ha 1 foot 102 t ha 1 reference soils 291 t ha 1 implying a variation in nutrient storage of the same order in the head area only the oldest landslide had an organic layer all mineral soils were acidic ph in h2o of the a horizon 3 4 5 2 the effective cec of the a horizon ranged from 22 to 141 mmolc kg 1 and the base saturation from 13 to 54 none of these properties was consistently different between landslide and reference soils the a horizons of the soil in the landslide foot area had greater concentrations of most nutrients than those in the landslide head area however differences were not significant the nutrient concentrations in the landslide foot area resembled those in the a horizons of the reference soils thus the most obvious change in soil properties caused by the landsliding was partial or complete removal of the organic layer which was not restored during the ca 20 years covered by the chronosequence this decreased the topsoil fertility of the landslide area

landslides triggered by the 7 august 2009 typhoon morakot in southern taiwan abstract landslides triggered by typhoon morakot with an area over 576 m2 were mapped from formosat 2 images recognition and calculation of the number and area of landslides show that at least 22 705 landslides with a total area of 274 km2 were recognized in the 7811 km2 study area among these landslides 17 417 with a total area of 150 km2 are recognized as new ones and 5288 with a total area of 124 km2 are classified as enlarged from pre existing ones out of the 22 705 landslides there were 22 221 recognized with an area smaller than 10 ha 298 recognized in the range of 10 to 20 ha twenty two landslides with an area of over 60 ha have also been identified and the total area of these landslides is 20 km2 which is equal to 7 37 of the total landslide area with respect to exposed rock type the landslides mainly occurred in eocene miocene slate and miocene sandstone and shale in addition morakot induced landslides mainly occurred in areas with cumulative precipitation in the range of 800 to 2600 mm and the magnitude of landslide concentration is roughly linearly proportional to the amount of cumulative rainfall

the isotopic composition of particulate organic carbon in mountain rivers of taiwan small rivers draining mountain islands are important in the transfer of terrestrial particulate organic carbon poc to the oceans this input has implications for the geochemical stratigraphic record we have investigated the stable isotopic composition of poc 13corg in rivers draining the mountains of taiwan in 15 rivers the suspended load has a mean 13corg that ranges from 28 1 0 8 to 22 0 0 2 on average 37 samples per river over the interval of our study to investigate this variability we have supplemented suspended load data with measurements of poc in bedrock and river bed materials and constraints on the composition of the terrestrial biomass fossil poc in bedrock has a range in 13corg from 25 4 1 5 to 19 7 2 3 between the major geological formations using coupled 13corg and n c we have found evidence in the suspended load for mixing of fossil poc with non fossil poc from the biosphere in two rivers outside the taiwan central range anthropogenic land use appears to influence 13corg resulting in more variable and lower values than elsewhere in all other catchments we have found that 5 variability in 13corg is not controlled by the variable composition of the biomass but instead by heterogeneous fossil poc in order to quantify the fraction of suspended load poc derived from non fossil sources fnf as well as the isotopic composition of fossil poc 13cfossil carried by rivers we adapt an end member mixing model river suspended sediments and bed sediments indicate that mixing of fossil poc results in a negative trend between n c and 13corg that is distinct from the addition of non fossil poc collapsing multiple fossil poc end members onto a single mixing trend as an independent test of the model fnf reproduces the fraction modern fmod in our samples determined from 14c measurements to within 0 09 at the 95 confidence level over the sampling period the mean fnf of suspended load poc was low 0 29 0 02 n 459 in agreement with observations from other mountain rivers where physical erosion rates are high and fossil poc enters river channels the mean 13cfossil in suspended poc varied between 25 2 0 5 and 20 2 0 6 from catchment to catchment this variability is primarily controlled by the distribution of the major geological formations it also covers entirely the range of 13corg found in marine sediments which is commonly thought to derive from mixing between marine and terrigenous poc if land sourced poc is preserved in marine sediments then changes in the bulk 13corg observed offshore taiwan could instead be explained by changes in the onshore provenance of sediment the range in 13corg of fossil organic matter in sedimentary rocks exposed at the surface is large and given the importance of these rocks as a source of clastic sediment to the oceans care should be taken in accounting for fossil poc in marine deposits supplied by active mountain belts

structural evolution metamorphism and restoration of the arabian continental margin saih hatat region oman mountains abstract 170 m y of relatively stable passive margin sedimentation along the northern continental margin of arabia was abruptly terminated during the cenomanian turonian 95 ma when the oman continental margin collapsed and subsided rapidly aruma basin to accommodate obduction of the semail ophiolite complex and underlying thrust sheets haybi and hawasina complexes in the oman mountains the ophiolite was emplaced at least 200 km over the passive margin probably over 450 km in total from ne to sw during the later stages of obduction the leading edge of the continental margin was subducted to depths where carpholite bearing rocks 6 8 kbar blueschist 12 15 kbar and eclogite ca 20 kbar facies metamorphism formed in a ductile deforming ne dipping subduction zone along the northeastern margin of the saih hatat culmination in ne oman the mesozoic shelf carbonates are deformed by recumbent folding on all scales the present day structure is dominated by four sw vergent thrust slices in carpholite grade rocks at higher structural levels overlying lower units of crossite bearing blueschist hulw unit garnet glaucophane chloritoid blueschists and garnet clinopyroxene phengite glaucophane eclogites 15 20 kbar the largest shear zone separates 7 8 kbar hulw unit blueschists above from 12 15 kbar retrogressed eclogites and ca 20 kbar eclogites of the as sifah unit below further inboard sw a major shear zone separates the lower plate hulw blueschist facies rocks from the upper plate sedimentary rocks upper plate lower plate discontinuity which also show carpholite grade hp metamorphism towards the ne restoration of the entire saih hatat continental margin shows that the upper plate lower plate discontinuity cuts down section to the sw as far as the proterozoic hatat schists ne directed extensional crenulation schistosity and nne oriented stretching lineations in the eclogite and blueschist facies rocks are consistent with sw directed exhumation of footwall hp rocks ne facing folds and spectacular sheath folds with greatly attenuated limbs in the upper plate sediments are interpreted as antithetic backfolds with shortening in the upper plate balanced by the subduction of the lower plate consistent with a ne directed subduction of the continental margin rocks beneath the sw obducting ophiolite haybi and hawasina thrust sheets recent suggestions of a nascent sw directed subduction beneath the oman margin are not consistent with the sedimentary evolution of the shelf and slope carbonates or the geological structure of saih hatat two main phases of tectonic uplift of saih hatat and jebel akhdar are firstly the latest cretaceous ramp culmination associated with foreland propagating thrusts in the sw and backfolds in the ne and secondly post late eocene oligocene uplift by ca 2000 m

climate regulates the erosional carbon export from the terrestrial biosphere erosion drives the export of particulate organic carbon from the terrestrial biosphere pocbiosphere and its delivery to rivers the carbon transfer is globally significant and can result in drawdown of atmospheric carbon dioxide co2 if the eroded pocbiosphere escapes degradation during river transfer and sedimentary deposition despite this recognition we lack a global perspective on how the tectonic and climatic factors which govern physical erosion regulate pocbiosphere discharge obscuring linkages between mountain building climate and co2 drawdown to fill this deficit geochemical 13c 14c and c n hydrometric water discharge suspended sediment concentration and geomorphic slope measurements are combined from 33 globally distributed forested mountain catchments radiocarbon activity is used to account for rock derived organic carbon and reveals that pocbiosphere eroded from mountain forests is mostly 1300 14c years old annual pocbiosphere yields are positively correlated with suspended sediment yields confirming results from taiwan and a recent global analysis and are high in catchments with the steepest slopes based on these relationships and the global distribution of slope angles 3 arc second it is suggested that topography steeper than 10 16 of the continental area may contribute 40 of global pocbiosphere erosional flux climate is shown to regulate pocbiosphere discharge by mountain rivers by controlling hydrologically driven erosion processes in catchments where discharge measurements are available 8 of the 33 a significant relationship exists between daily runoff mm day 1 and pocbiosphere concentration mg l 1 r 0 53 p 0 0001 the relationship can be described by a single power law and suggests a high connectivity between forested hillslopes and mountain river channels as a result annual pocbiosphere yields are significantly correlated with mean annual runoff r 0 64 p 0 0001 a shear stress pocbiosphere erosion model is proposed which can explain the patterns in the data the model allows the climate sensitivity of this carbon flux to be assessed for the first time for a 1 increase in annual runoff pocbiosphere discharge is predicted to increase by 4 in steeper catchments pocbiosphere discharge increases more rapidly with an increase in annual runoff for comparison a 1 increase in annual runoff is predicted to increase carbon transfers by silicate weathering solute fluxes in mountains by 0 4 0 7 depending on the fate of the eroded pocbiosphere river export of pocbiosphere from mountains may act as an important negative feedback on rising atmospheric co2 and increased global temperature erosion of carbon from the terrestrial biosphere links mountain building and climate to the geological evolution of atmospheric co2 while the carbon fluxes are sensitive to predicted changes in runoff over the coming century

regional soil erosion in response to land use and increased typhoon frequency and intensity taiwan reservoir sedimentation data and sediment yields from taiwanese rivers show increased soil erosion in response to both 20th century changes in land use and a more recent increase in typhoon frequency and intensity decadal variations of up to 5 to 20 fold in suspended sediment rating curves demonstrate supply limited transport and correspond to increased sediment delivery from hillslopes due to changes in land use regional ground shaking during the chi chi earthquake and post 2000 changes in typhoon frequency and intensity while accelerated erosion in central taiwan after the chi chi earthquake has been documented previously our results show that periods of increased upland erosion also occurred earlier in response to 20th century changes in land use analyses of rainfall records and typhoon frequency for the period 1900 2009 further point to an island wide increase in erosion rates corresponding to increased typhoon frequency and intensity after 1990

the transfer of modern organic carbon by landslide activity in tropical montane ecosystems 1 geomorphic processes play an important role in the transfer and storage of carbon within steep mountainous terrain among these mass wasting stands out because of its impact on above and below ground carbon pools and its potential for releasing or sequestering carbon a combined remote sensing and gis modeling approach was used to quantify the amount and spatial redistribution of modern organic carbon mobilized by mass wasting activity in a tropical mountain setting the study focused on a population of hundreds of shallow translational landslides triggered by hurricane mitch 1998 on seven watersheds draining the southern flank of the sierra de las minas mountain range slm in central eastern guatemala results illustrate that mass wasting contributed to the transfer of 43 104mgc or 3 of the pre event c in above ground vegetation and soils for an equivalent carbon flux rate of 0 08 0 33 mgc ha 1 y 1 depending on whether we consider hurricane mitch to be a landslide triggering event with a 20 year or an 80 year recurrence interval while 30 of this carbon was delivered to hillslopes or first order streams with a presumed high potential for long term sequestration the remaining 70 was delivered to higher order streams with unknown carbon retention capabilities therefore the ultimate fate of the carbon released by landsliding is very uncertain but depending on the proportion sequestered by colluvial deposits the recurrence interval of landslide triggering events and the rate of ecosystem recuperation at the landslide failure sites mass wasting could be either a net source or sink of carbon in a simulated setting based on the slm study results in which all carbon transferred by landslides from all tropical mountains of the globe is released to the atmosphere it would represent an amount equivalent to 1 11 of the global carbon currently being released by the burning of fossil fuels meanwhile in a projected scenario where a significant proportion of the carbon transferred by landslides is retained within sedimentary deposits sequestration rates would equal 2 19 of the residual land sink

structure and metamorphism of blueschist eclogite facies rocks from the northeastern oman mountains the northern part of the saih hatat window oman shows high pressure metamorphic rocks derived from shelf sediments and pre premian continental basement and is atypical of sub ophiolite metamorphism elsewhere the high pressure rocks are divided into structural units originally bounded by foreland propagating thrusts formed during ophiolite obduction although now many contacts are backthrusts normal faults or extensional shear zones metamorphic breaks exist across many unit boundaries the deepest unit as sifah has eclogite facies assemblages in metabasites and metapelites which record evolution of p t conditions along a clockwise path culminating al 23 2 5kbar 540 75 c contrasting markedly with overlying units 5 10 kbar 200 500 c although separated by 40 ar 39 ar apparent ages our tectonic model relates all the high p units to a single convergent event in the late cretaceous the as sifah eclogites were exhumed in two stages i tectonic emplacement against other units at c 20 25 km depth and ii exhumation of the entire high p zone by culmination collapse after obduction

extreme storm events landscape denudation and carbon sequestration typhoon mindulle choshui river taiwan we have performed the first known semicontinuous monitoring of particulate organic carbon poc fluxes and dissolved si concentrations delivered to the ocean during a typhoon sampling of the choshui river in taiwan during typhoon mindulle in 2004 revealed a poc flux of 5 00 105 t associated with a sediment flux of 61 mt during a 96 h period the linkage of high amounts of poc with sediment concentrations capable of generating a hyperpycnal plume upon reaching the ocean provides the first known evidence for the rapid delivery and burial of poc from the terrestrial system these fluxes when combined with storm derived co2 consumption of 1 65 108 mol from silicate weathering elucidate the important role of these tropical cyclone events on small mountainous rivers as a global sink of co2

oman exotics oceanic carbonate build ups associated with the early stages of continental rifting the so called oman exotic limestones form isolated masses from boulder size to 1 000 m thick of middle to upper permian and upper triassic fossiliferous limestones and crop out within imbricated thrust slices beneath the semail ophiolite in the oman mountains permian exotics are of dominantly reef and forereef facies whereas triassic exotics are more typically of back reef and lagoonal facies they are commonly associated with a substrate of alkalic and transitional tholeiitic basalts and are interpreted as a series of reef associated carbonate buildups deposited in part on oceanic islands or seamounts close to the site of initial rifting of the oman continental margin

weathering and vegetation effects in early stages of soil formation abstract bedrock surfaces in the ouachita mountains arkansas exposed by spillway construction and which had not previously been subjected to surface weathering environments developed 15 20 cm thick soil covers in less than three decades all open bedrock joints showed evidence of weathering and biological activity rock surfaces and fragments also showed evidence of significant weathering alteration the results suggest a soil production function whereby weathering and increases in thickness are initially rapid the rapid initial rate 5 to 10 mm year 1 is facilitated by a weathering favorable regional climate local topography favoring moisture and sediment accumulation and aggressive vegetation colonization the ages of the trees on the bedrock benches suggests that a short period