metasomatic replacement in the skaergaard intrusion east greenland preliminary observations abstract several unusual types of replacement structures in the layered series and marginal border series of the skaergaard intrusion indicate that metasomatic changes have altered the modal proportions and in places the mineral composition of the gabbro the geometrical forms and compositional patterns of these features indicate that they result from reactive fluids moving through the rocks at high temperatures shortly after the magma had reached an advanced stage of crystallization the principal effect of metasomatism has been to produce strongly contrasting mafic and felsic rocks

crustal xenoliths in recent hawaiites from mount etna italy evidence for alkali exchanges during magma wall rock interaction abstract detailed mineralogical and geochemical systematics were carried out on crustal xenoliths the host hawaiite lavas erupted from mount etna sicily italy in 1892 1986 and 1989 as well as the flyschs from the volcano basement the xenoliths suffered morphological structural mineralogical and geochemical alteration induced by thermal and chemical exchange with the enclosing lava high temperature reactions and partial or complete melting as well as different mechanisms of elemental interdiffusion took place their exact nature depending on the type of xenolith an early and strong mobility of k rb and cs and their selective migration towards the anatectic melts the lava envelope was observed at both mineral phase and whole rock scales this is closely connected to a release of h 2 o cl s and co 2 associated with the dehydration and the decarbonation of the sediments thus the selective migration of the k rb and cs towards the enclosing lava as well as contamination of the host lava observed seems to be induced by a selective diffusion of alkalis away from the anatectic melts and especially by their selective transfer through the action of complex interstitial and chemically active fluids such processes might be connected to the strong enrichment in k rb and cs of the recent hawaiites from mount etna they might also substantiate the hypothesis that these enrichments result from selective contamination of the magma as a consequence of the percolation or circulation of a carrier fluid phase through the upper parts of the magmatic feeding system

the significance of channel recharge rates for estimating debris flow magnitude and frequency the quantification of debris flow hazard requires estimates of debris flow frequency and magnitude several methods have been proposed to determine the probable volume of future debris flows from a given basin but most have neglected to account for debris recharge rates over time which may lead to underestimation of debris flow volumes in basins with rare debris flows this paper deals with the determination of debris recharge rates in debris flow channels based on knowledge of debris storage and the elapsed time since the last debris flow data are obtained from coastal british columbia and a relation is obtained across a sample of basins with similar terrain and climatic conditions for rennell sound on the west coast of the queen charlotte islands the power law relation for area normalized recharge rate rt versus elapsed time te was rt 0 23te 0 58 with an explained variance of 75 per cent a difference in recharge rates may exist between creeks in logged and unlogged forested terrain the power function for undisturbed terrain was rt 0 20te 0 49 while the function for logged areas was rt 0 30te 0 77 this result suggests that for the same elapsed time since the last debris flow clearcut gullies tend to recharge at a slower rate than creeks in old growth forest this finding requires verification particularly for longer elapsed times since debris flow but would have important implications for forest resource management in steep coastal terrain this study demonstrates that commonly used encounter probability equations are inappropriate for recharge limited debris flow channels copyright 2005 john wiley sons ltd

the effects of logging on frequency and distribution of landslides in three watersheds on vancouver island british columbia abstract three hundred and sixty three landslides in three watersheds that totaled 382 km2 were identified from air photographs beginning at a date that preceded logging to the present the three watersheds all lie on vancouver island however they have different precipitation regimes topography and amounts logged landslide areas in the watersheds varied in size from 200 m2 to more than 1 ha nearly 80 of the landslides were debris slides 15 were debris flows and the remainder primarily rock falls following logging the number of landslides increased substantially in all watersheds although the amount of increase was variable approximately 11 3 and 16 times in macktush creek artlish river and nahwitti river respectively other analyses of changes in landslide density also produced highly variable results with the number of landslides increasing between 2 4 and 24 times further 2 12 times more landslides reached streams following logging activities densities for landslides impacting streams increased for the period of record from 1 5 to 10 times following logging activities the densities were substantially greater where only landslides that reached streams since development began in a watershed were considered roads had the greatest spatial impact in the watersheds compared to their total area with frequencies determined to have increased by 27 12 and 94 times for macktush artlish and nahwitti respectively the results highlight the relative impact of roads and their role in slope stability

estimates of three dimensional rupture surface geometry of deep seated landslides using landslide inventories and high resolution topographic data abstract deep seated landslides cause significant damage to the built environment characterizing the shear surface and volume of these features is often limited to intensive site specific monitoring or at a larger scale generalized empirical relationships developed from change analysis however there is limited means of generalizing regional scale rupture surface information for deep seated landslides where deposits still overlay much of the failure surface herein a method is proposed that uses high resolution bare earth digital elevation models with an inventory of mapped landslide extents to gather first order estimates of three dimensional rupture surface geometries and volumes for rotational and compound landslide features at a regional scale this approach is first calibrated to a suite of well characterized landslides and then applied to over eight hundred deep seated landslides in three different geologic regimes estimates of landslide area volume relationships are proposed that are consistent with previous empirical assessments the aforementioned relationships describe mean landslide thickness added relationships relating landslide area to maximum landslide thickness are proposed the presented results suggest limits on magnitudes of depth with landslide classification and relief between geologic settings consistent with prior research it is observed that landslide area exhibits a first order control on maximum and mean landslide thickness but further insight is provided towards the influence of a limited set of landslide classification which exhibit controls on the range of magnitudes observed for maximum landslide depth associated with failure lastly the implications and limitations of the developed three dimensional mapping approach is discussed

morphological and sedimentological responses of small stream channels to extreme rainfall and land use in the darjeeling himalayas abstract three pairs of small fourth to sixth order catchments approximately 5 80 km2 draining the margin of the darjeeling himalayas into the piedmont were selected for a comparison of the land use impact on the morphology and sedimentology of their stream channels each pair experienced similar annual rainfall and comprised similar metamorphic bedrock steep topography and brown soils the members of each pair contrast with respect to their land use structure as they comprise large forest cover forest 90 and a significant contribution of agricultural land with tea plantations forest

paleoproterozoic gold deposits hosted by albite and carbonate altered tonalite in the chirano district ghana west africa paleoproterozoic birimian supergroup rocks of southwest ghana host numerous mesothermal lode gold deposits including the 38 million ounce moz ashanti deposit at obuasi and other multimillion ounce deposits at bogoso konongo prestea bibiani and in the yamfo sefwi region gold deposits of the chirano district are localized along the chirano lode horizon a 9 km segment of the chirano and related shear zones on the southeast margin of the sefwi bibiani belt economically significant mineralization at chirano is largely hosted by altered tonalite intrusions weaker alteration and subparts per million gold grades extend into adjacent birimian mafic igneous rocks and tarkwaian group sedimentary rocks pink albite alteration albite quartz pyrite hematite rutile leucoxene chalcopyrite gold and later pale carbonate alteration ankerite sericite quartz pyrite hematite gold fineness 910 940 ag au telluride characterize the gold deposits of the chirano district alteration assemblages and the bi te and mo contents of the mineralized rocks at chirano are more typical of lode gold deposits than orthomagmatic gold deposits alteration assemblages at chirano contrast with the graphite carbonate pyrite arsenopyrite pyrrhotite assemblages that dominate the lode gold deposits in southwest ghana which are hosted by graphitic shear zones and birimian sedimentary rocks differences between alteration assemblages at chirano and those in graphitic shear zones may reflect the different wall rock assemblages with which the hydrothermal fluid equilibrated rather than different fluid sources mineralization in the chirano district formed during a relatively late episode of small displacement brittle cataclasis on the chirano lode horizon after reverse ductile shearing associated with regional scale shortening this structural history is similar to that documented at the larger ashanti and bogoso deposits on the opposite side of the kumasi basin timing relationships are compatible with all three deposits forming during a single mineralizing event late in the eburnean 2 orogeny at chirano limited fault vein geometric relationships imply a component of reverse movement during mineralization whereas sinistral strike slip movement accompanied mineralization at ashanti and bogoso no consistent correlation was observed between the asymmetry of bends and splays in the strike of the chirano lode horizon and the location or style of individual gold deposits unlike at ashanti and bogoso the structural settings of deposits in the chirano district indicate that an exploration strategy which assumes mineralization occurred during sinistral offset in the host structures similar to relationships at ashanti and bogoso may result in significant targets being ignored

the early proterozoic birimian supergroup of ghana and some aspects of its associated gold mineralization abstract rocks of the birimian supergroup of early proterozoic age sm nd isochron age 2166 66 ma form part of the west african craton ghana contains the eastern portion of the birimian terrane five parallel evenly spaced several hundred kilometre long volcanic belts consisting mainly of low grade metamorphic tholeiitic lavas morb chemistry characterize the birimian supergroup of ghana the belts are separated by basins containing isoclinally folded dacitic volcaniclastics wackes and argillitic sediments as well as granitoids lavas and sedimentary rocks were deposited contemporaneously as lateral facies equivalents within the sedimentary basins various lithofacies are distinguished in the transition zone between belt volcanics and basin sediments a chemical facies occurs this is defined by cherts manganiferous and carbon rich sediments fe ca mg carbonates and sulphide mineral disseminations after their emplacement birimian lavas and sediments were folded in the course of the eburnean tectono thermal event intruded by various types of granitoids uplifted and eroded the erosion products were deposited as sediments of the tarkwaian group in long narrow intramontane grabens which formed due to rifting preferentially in the central portions of all five birimian volcanic belts tarkwaian sediments were deformed by gravity tectonics two major types of eburnean granitoids in ghana are characterized as follows basin granitoids cape coast type occur as synorogenic foliated batholiths chiefly in the central portions of birimian sedimentary basins they are peraluminous and generally granodioritic in composition belt granitoids dixcove type mostly form late orogenic unfoliated intrusions in volcanic belts they possess a metaluminous character and commonly are of tonalitic composition bongo granitoids are of post tarkwaian age and k rich in contrast to these granitoid types which have strong mantle affinities the winneba type had an archean sialic precursor a model involving small scale equidimensional parallel and contemporaneously operating convection cells in the upper mantle which caused rifting of a highly attenuated protocrust as well as linear eruptions of tholeiitic magmas is proposed recent sm nd pb pb and rb sr data of volcanic and plutonic rocks are incorporated most ghanaian birimian gold occurrences and mines are concentrated in narrow corridors of 10 15 km width in the transition zone between volcanic belts and sedimentary basins as are the chemical facies and regionally extensive shear zones at the volcanics sediment interface birimian gold in ghana is present as two major types 1 the disseminated sulphide type which is generally lithofacies controlled i e controlled by chemical sediments and to a lesser extent by selvages of gold quartz veins and 2 the quartz vein type which is exclusively structure controlled data on geochemical underground traverses across both types of gold mineralization are briefly summarized

effect of forest clear cutting on landslide occurrences analysis of rainfall thresholds at mt ichifusa japan abstract vegetation cover is an important factor for rainfall induced landslides we analyzed the effect of forest clear cutting on the initiation of landslides using empirical rainfall intensity duration i d thresholds at mt ichifusa japan which is characterized by granitic rocks extensive clear cutting was conducted for the forest industry during the late 1960s in the northern part of mt ichifusa this single episode of clear cutting caused frequent shallow landslides triggered by rainfall we interpreted orthorectified aerial photographs from 1969 1976 1980 1985 1990 1995 1999 and 2005 using gis and mapped landslides based on these photographs we then analyzed all rainfall events of the warm seasons apr oct of 1952 2011 60 years based on hourly rain gauge data we used basic rainfall parameters such as mean rainfall intensity i mm h and duration d h and estimated the return periods of these rainfall conditions we investigated rainfall i d thresholds for landslide occurrences in each period represented by the aerial photographs and assessed the relationships between landslide occurrences and topographic characteristics from 10 m dems the results show that several landslides occurred after clear cutting before 1976 but that they have occurred most frequently during the periods 1976 1980 1980 1985 and 1990 1995 numerous landslides occurred in these years at steeper and gentler slopes in the clear cut area but few landslides occurred in the non clear cut area rainfall analysis demonstrates that rainfall i d thresholds after clear cutting declined to half of those of the non clear cut area the return periods of these rainfall i d thresholds also declined to 1 year for short durations of

bed load transport in managed steep gradient headwater streams of southeastern alaska 1 bed load transport was investigated in four headwater streams in southeastern alaska subjected to different management and disturbance regimes bed load yield was positively correlated to peak discharge during the fall 1999 monitoring period fine bed load materials 1 11 mm that were supplied from hillslope sources were equally mobilized during most storm events medium sized bed materials 11 200 m were only partially mobilized even during large storms whereas large particles 200 mm were immobile and often formed interlocking channel structures the transport distances of medium size materials depended on amount of channel obstructions e g woody debris and sediment supply conditions both of these factors were influenced by the occurrence of mass movement timber harvesting and the related recovery processes the highest total bed load yield was observed in a channel affected by a debris flow in 1993 total sediment yields are similar among channels with old growth clear cut logged 4 years before monitoring and young alder affected by landslides and debris flows in 1961 riparian stands by comparing the old growth and young alder channels it appears that bed load yield recovers from debris flow disturbances in about 40 years however recovery of channel conditions e g reach types and woody debris may take much longer effects of timber harvesting on bed load transport are controlled by sediment linkages between hillslopes and channels related to the occurrence of mass movement

the hydrothermal fluid of archaean lode gold deposits at different metamorphic grades compositional constraints from ore and wallrock alteration assemblages a low salinity mixed aqueous carbonic fluid is common to all archaean lode gold deposits throughout the range of mineralising conditions from sub greenschist to lower granulite facies temperatures alteration assemblages and fluid inclusion data give constraints on the fluid composition fluid xco2 is 0 1 0 3 in typical greenschist facies mesothermal deposits at higher temperatures the assemblages are consistent with formation from a fluid of similar composition but slightly higher or lower xco2 cannot be ruled out and fluid inclusion data indicate that ch4 may be an important component in ore fluids at these temperatures fluid ph is neutral or weakly alkaline at all conditions a range of relative oxidation states of four orders of magnitude fo2 is indicated at any temperature with deposits more oxidising relative to qfm at lower temperature sulphur contents of the fluids vary from 10 to 10 3 5m s with a trend towards lower sulphur contents at lower temperatures the relative concentrations of major cations in solution are similar at all conditions with na k ca although ca may be less abundant at low temperatures the broad similarities in ore fluid composition at all temperatures give support to crustal continuum models in which archaean lode gold mineralisation involved either a single fluid moving through the middle and upper crust or derivation of ore fluids by similar processes at different crustal levels many of the compositional differences between high and lowtemperature ore fluids may be attributed to evolution of deep sourced hydrothermal solutions as they rise along structurally controlled conduits the constancy of major ore fluid component concentration e g co2 cl k suggests fluid buffering and high fluid rock ratios along fluid pathways fluid buffered conditions can also explain the ore fluid fo2 temperature relations with equilibria between oxidised and reduced aqueous carbon or sulphur species controlling the oxidation state in contrast the concentrations of components present in lesser abundance in archaean gold ore fluids e g s ca h were probably controlled either by saturation of one or more mineral phases brought on by decreasing temperature or were rock buffered through fluid rock reactions extrapolation to high temperatures of the k na and ca contents of the gold bearing fluids indicates that their composition is consistent with derivation from or final equilibration with rocks of intermediate granitic composition thus giving support to isotopic and geological arguments for ore fluid source regions external to the greenstone belts the fluid oxidation states are characteristic of a wide range of potential source rocks including mantle derived igneous rocks calc alkaline granitoids and magmas and seaflooraltered metabasalts strongly oxidised magmatic sources or unusually oxidising source processes e g co2 streaming during granulitisation of the lower crust are therefore not required in the genesis of arch an lode gold deposits

hydrogeomorphic linkages of sediment transport in headwater streams maybeso experimental forest southeast alaska hydrogemorphic linkages related to sediment transport in headwater streams following basin wide clear cut logging on prince of wales island southeast alaska were investigated landslides and debris flows transported sediment and woody debris in headwater tributaries in 1961 1979 and 1993 widespread landsliding in 1961 and 1993 was triggered by rainstorms with recurrence intervals 24 h precipitation of 7 0 years and 4 2 years respectively occurrence distribution and downstream effects of these mass movements were controlled by landform characteristics such as channel gradient and valley configuration landslides and channelized debris flows created exposed bedrock reaches log jams fans and abandoned channels the terminus of the deposits did not enter main channels because debris flows spread and thinned on the unconfined bottom of the u shaped glaciated valley chronic sediment input to channels included surface erosion of exposed till rain splash sheet erosion and freeze thaw action and bank failures bedload sediment transport in a channel impacted by 1993 landslides and debris flows was two to ten times greater and relatively finer compared with bedload transport in a young alder riparian channel that had last experienced a landslide and debris flow in 1961 sediment transport and storage were influenced by regeneration of riparian vegetation storage behind recruited woody debris development of a streambed armour layer and the decoupling of hillslopes and channels both spatial and temporal variations of sediment movement and riparian condition are important factors in understanding material transport within headwaters and through channel networks copyright 2004 john wiley sons ltd

the influence of dikes on auriferous shear zone development within granitoid intrusions the bourlamaque pluton val d or district abitibi greenstone belt shear zone related gold quartz veins in granitoid intrusions are commonly intimately associated with mafic dikes which may have a profound influence on the localization orientation and kinematics of auriferous shear zones the bourlamaque pluton of the val d or district contains several economic auriferous shear zones most of which follow and overprint diorite dikes mineralization in all deposits consists of quartz tourmaline pyrite veins in reverse oblique orientation with a significant range of strike dip and slip direction the geometry and kinematics of shear zone and vein array within the pluton is more complex than the simple conjugate pattern predicted for a deforming homogeneous intrusion the stress tensor determined from the auriferous shear zones within the pluton indicates the same northerly directed compression recorded by similar shear zones outside the pluton this indicates that the complex shear zone and vein pattern within the pluton reflects the influence of diorite dikes which

forecasting the magnitude of potential landslides based on insar techniques abstract a new method combining empirical modeling with time series interferometric synthetic aperture radar insar data is proposed to provide an assessment of potential landslide volume and area the method was developed to evaluate potential landslides in the heitai river terrace of the yellow river in central gansu province china the elevated terrace has a substantial loess cover and along the terrace edges many landslides have been triggered by gradually rising groundwater levels following continuous irrigation since 1968 these landslides can have significant impact on communities affecting lives and livelihoods developing effective landslide risk management requires better understanding of potential landslide magnitude fifty mapped landslides were used to construct an empirical power law relationship linking landslide area al to volume vl vl 0 333 al1 399 insar derived ground displacement ranges from 64 mm y to 24 mm y along line of sight los further interpretation of patterns based on remote sensing insar optical image and field survey enabled the identification of an additional 54 potential landslides 1 9 102 m2 al 8 1 104 m2 in turn this enabled construction of a map that shows the magnitude of potential landslide activity this research provides significant further scientific insights to inform landslide hazard and risk management in a context of ongoing landscape evolution it also provides further evidence that this methodology can be used to quantify the magnitude of potential landslides and thus contribute essential information towards landslide risk management

increased landslide activity on forested hillslopes following two recent volcanic eruptions in chile large explosive eruptions can bury landscapes beneath thick layers of tephra rivers subsequently overloaded with excess pyroclastic sediments have some of the highest reported specific sediment yields much less is known about how hillslopes respond to tephra loads here we report a pulsed and distinctly delayed increase in landslide activity following the eruptions of the chaiten 2008 and puyehue cordon caulle 2011 volcanoes in southern chile remote sensing data reveal that landslides clustered in densely forested hillslopes mostly two to six years after being covered by tephra this lagged instability is consistent with a gradual loss of shear strength of decaying tree roots in areas of high tephra loads surrounding areas with comparable topography forest cover rainfall and lithology maintained landslide rates roughly ten times lower the landslides eroded the landscape by up to 4 8 mm on average within 30 km of both volcanoes mobilizing up to 1 6 mtc at rates of about 265 tc km 2 yr 1 we suggest that these yields may reinforce the elevated river loads of sediment and organic carbon in the decade after the eruptions we recommend that studies of post eruptive mass fluxes and hazards include lagged landslide responses of tephra covered forested hillslopes to avoid substantial underestimates a delayed increase of landslide activity occurred about two to six years after two volcanic eruptions in chile in 2008 and 2011 according to remote sensing data the time lag is consistent with decaying tree roots in areas covered by tephra

gold mineralization in as rich mesothermal gold ores of the bogosu prestea mining district of the ashanti gold belt ghana remobilization of invisible gold the bogosu prestea mining district of southwestern ghana is a 33 km section of the early proterozoic ashanti gold belt greenschist facies carbonaceous and carbonate bearing turbidites and greywackes and mafic dikes host numerous economic mesothermal gold deposits structurally higher ores in the bogosu concession have brittle deformation and consist of disseminated sulphide lodes in tectonically disrupted sedimentary rocks and carbonate altered mafic dikes most gold occurs as micrometre size particles in arsenian pyrite and as invisible gold in arsenian pyrite and arsenopyrite the structurally deeper ores of the adjoining prestea concession are associated with brittle ductile deformation and consist of extensive crack seal quartz veins and graphitic shear zones only minor amounts of invisible gold were detected in these deeper lodes gold occurs dominantly as abundant microscopic and larger particles in sulphide arsenide minerals and in gangue the gold distribution patterns revealed by sims microprobe analysis and ion maps emp and colour staining suggest that most of the primary gold in the bogosu prestea system precipitated in solid solution with sulphide arsenide minerals however post depositional concentration and redistribution occurred in increasing degree with 1 increase in metamorphic hydrothermal gradients in the gold system depth 2 decrease in the refractory properties of the host mineral and 3 increase in the amount of post depositional host mineral recrystallization and deformation gold evolved from primary solid solution within sulphide arsenide minerals to colloidal and micrometre size particles concentrated in voids fractures and internal grain boundaries and finally to microscopic and larger particles at sulphide arsenide grain margins and in the gangue assemblage the general conclusions presented here are applicable to as rich gold deposits of all ages worldwide the presence of gold in late fractures is insufficient evidence for late stage introduction of gold in mesothermal gold systems

the silidor deposit rouyn noranda district abitibi belt geology structural evolution and paleostress modeling of an au quartz vein type deposit in an archean trondhjemite late orogenic gold bearing quartz vein deposits within the rouyn noranda mining district occur mainly within archean tonalitic plutons of the blake river group southern abitibi belt the silidor deposit is a representative example of a pluton hosted lode gold deposit the silidor mine contained 2 95 million tons mt mined and estimated reserves grading 5 1 g t au 15 t au the mineralized zone is 900 m in length and has a vertical extent of 900 m an average thickness of 3 5 m and trends northwest southeast with a dip of 50 to 70 ne its alteration envelope consists of a red hematite altered trondhjemite measured 18 o values for quartz veins 7 7 10 9 and 34 s values for pyrite 6 1 to 9 4 imply oxidizing conditions during gold deposition the mineralized zone comprises vein quartz white gray and smoky varieties beige mineralized trondhjemite and green carbonate sericite fuchsite breccia which resulted from shearing and metasomatism of an early northwest southeast dioritic dike a quantitative microtectonic study 400 measurements was carried out on the powell tonalitic sill in the silidor mine area to reconstruct the deformation before during and after the mineralizing events the reduced stress tensors display large variations in 1 orientation trending successively northwest southeast northeast southwest and finally north south the silidor deposit is the result of several vein filling events which occurred during evolution from strike slip faulting to reverse faulting regimes with 1 remaining northeast southwest but with exchange of orientation of 2 and 3 such variations may reflect an oblique collision and processes of stress permutation paleostress mapping of archean terranes can be used as a targeting tool for mesothermal lode gold deposits reduced stress tensors were used for the computation of paleostress maps using a distinct element model the silidor au quartz mineralization appears on these paleostress maps in an area characterized by low mean stress throughout the deformation history of the area near the horne creek fault this study emphasizes the role of second order faulting in the location of low and high pressure zones in the archean crust and the possible role of a tectonic indentor in the location of au mineralization

effects of forest harvesting on the occurrence of landslides and debris flows in steep terrain of central japan landslides and debris flows associated with forest harvesting can cause much destruction and the influence of the timing of harvesting on these mass wasting processes therefore needs to be assessed in order to protect aquatic ecosystems and develop improved strategies for disaster prevention we examined the effects of forest harvesting on the frequency of landslides and debris flows in the sanko catchment central japan using nine aerial photo periods covering 1964 to 2003 these photographs showed a mosaic of different forest ages attributable to the rotational management in this area since 1912 geology and slope gradient are rather uniformly distributed in the sanko catchment facilitating assessment of forest harvesting effects on mass wasting without complication of other factors trends of new landslides and debris flows correspond to changes in slope stability explained by root strength decay and recovery the direct impact of clearcutting on landslide occurrence was greatest in forest stands that were clearcut 1 to 10 yr earlier with progressively lesser impacts continuing up to 25 yr after harvesting sediment supply rate from landslides in forests clearcut 1 to 10 yr earlier was about 10 fold higher than in control sites total landslide volume in forest stands clearcut 0 to 25 yr earlier was 5 8 10 3 m 3 km 2 compared with 1 3 10 3 m 3 km 2 in clearcuts 25 yr indicating a fourfold increase compared with control sites during the period when harvesting affected slope stability because landslide scars continue to produce sediment after initial failure sediment supply from landslides continues for 45 yr in the sanko catchment to estimate the effect of forest harvesting and subsequent regeneration on the occurrence of mass wasting in other regions changes in root strength caused by decay and recovery of roots should be investigated for various species and environmental conditions copyright 2007 john wiley sons ltd

japan s sediment flux to the pacific ocean revisited abstract quantifying volumes and rates of delivery of terrestrial sediment from island arcs to subduction zones is indispensable for refining estimates of the thickness of trench fills that may eventually control the location and timing of submarine landslides and tsunami generating mega earthquakes despite these motivating insights knowledge about the rates of erosion and sediment export from the japanese islands to their pacific subduction zones remains patchy regardless of the increasing availability of highly resolved data on surface deformation climate geology and topography traditionally natural erosion rates across the island arc have been estimated from regression of topographic catchment metrics and reservoir sedimentation rates that were recorded over several years to decades we review current research in this context correct for a systematic bias in one of the most widely used predictions and present new estimates of decadal to millennial scale erosion rates of japan s terrestrial inner forearc we draw on several independent and unprecedented inventories of mass wasting reservoir sedimentation and concentrations of cosmogenic 10be in river sands we find that natural 10be derived denudation rates of several mm yr 1 in the japanese alps have been sustained over several centuries to millennia and are within error roughly consistent with sediment yields inferred from artificial reservoir sedimentation local exceptions may likely result from release of sediment storage or regional landsliding episodes that trigger transient sediment pulses our synopsis further reveals that catchments draining japan s eastern seaboard differ distinctly in their tectonic lithological topographic and climatic characteristics between the tohoku japanese alps and nankai inner forearc segments which is underscored by a marked asymmetric pattern of erosion rates along the island arc erosion rates are highest up to at least 3 mm yr 1 in the japanese alps that mark the collision of two subduction zones where high topographic relief hillslope and bedrock channel steepness foster rapid denudation by mass wasting comparable if slightly lower erosion rates characterise the nankai inner forearc in southwest japan most likely due to higher typhoon driven rainfall totals and variability rather than its high topographic relief in contrast our estimated erosion and flux rates are lowest in the tohoku inner forearc catchments that feed sediment into the japan trench we conclude that collisional mountain building of the japanese alps drives some of the highest erosion rates in the island arc despite similar uplift and precipitation controls in southwest japan we infer that prior to extensive river damming reservoir construction and coastal works the gross of japan s total sediment export to the pacific ocean entered the accretionary margin of the nankai trough as opposed to the comparatively sediment starved japan trench compared to documented contemporary rates of sediment flux from mountainous catchments elsewhere in the pacific the rivers draining japan s inner forearc take an intermediate position despite high relief steep slopes very high seismicity and frequent rainstorms however the average rates of millennial scale denudation in the japanese alps particularly are amongst the highest reported worldwide local mismatches between these late holocene and modern rates emphasise the anthropogenic fingerprint on sediment retention that may have significantly reduced the island arc s mass flux to its subduction zones as is the case elsewhere in east and southeast asia

the role of debris supply conditions in predicting debris flow activity debris flow frequency and magnitude were determined for 33 basins in southwest british columbia basins were first classifiedaseitherweathering limitedortransport limitedusingadiscriminantfunctionbasedondebris contributingarea an area weighted terrain stability number and drainage density multiple regression was used to predict magnitude peak discharge frequency and activity frequency times magnitude within each group of basins model performance was improved by stratifying the total sample of debris flow basins into weathering and transport limited groups explained varianceincreasedbyanaverageof15percentinthetransport limitedsample indicatingthatsedimentsupplyconditionsin themoreactivebasinsarefundamentalinpredictingdebrisflowactivity anindependenttestoftheregressionmodelswith 11basinsyieldedgenerallygoodresultsfordebrisflowmagnitudeandpeakdischarge predictionofdebrisflowfrequency provedproblematicalinweathering limitedbasins themethodsdevelopedhereprovideestimatesofdebrisflowattributes in basins for which few data on past events are available copyright 1999 john wiley sons ltd

application of a multi temporal lidar derived digital terrain model in a landslide volume estimation sediments produced by landslides are crucial in the sediment yield of a catchment debris flow forecasting and related hazard assessment on a regional scale however it is difficult and time consuming to measure the volumes of such sediment this paper uses a lidar derived digital terrain model dtm taken in 2005 and 2010 at 2 m resolution to accurately obtain landslide induced sediment volumes that resulted from a single catastrophic typhoon event in a heavily forested mountainous area of taiwan the landslides induced by typhoon morakot are mapped by comparison of 25 cm resolution aerial photographs taken before and after the typhoon in an 83 6 km2 study area each landslide volume is calculated by subtraction of the 2005 dtm from the 2010 dtm and the scaling relationship between landslide area and its volume are further regressed the relationship between volume and area are also determined for all the disturbed areas vl 0 452al1 242 and for the crown areas of the landslides vl 2 510al1 206 the uncertainty in estimated volume caused by use of the lidar dtms is discussed and the error in absolute volume estimation for landslides with an area 105 m2 is within 20 the volume area relationship obtained in this study is also validated in 11 small to medium sized catchments located outside the study area and there is good agreement between the calculation from dtms and the regression formula by comparison of debris volumes estimated in this study with previous work it is found that a wider volume variation exists that is directly proportional to the landslide area especially under a higher scaling exponent copyright 2013 john wiley sons ltd

complex mass wasting response of drainage basins to forest management in coastal british columbia the impacts of logging activities on mass wasting were examined in five watersheds in the coastal mountains of british columbia historical aerial photos were used to document mass wasting events and their occurrence was related to logging activities in the study basins logged and forested areas were compared in terms of mass wasting magnitude and frequency with reference to site characteristics the recovery time of the landscape after logging was assessed bedrock type and basin physiography had no identifiable effect on mass wasting frequency and magnitude mass wasting failure was primarily controlled by slope gradient basin vulnerability increased following clearcutting relative to forested areas in that mass wasting was initiated on gentler slopes the volume of sediment produced from logged slopes is of the same order as that from forested areas which are steeper by as much as 10 in both logged and forested areas the size distribution of mass wasting events follows an exponential distribution however the variability in mass wasting size in forested areas is much higher than that obtained for logged areas the recovery time after forest harvesting is over 20 years which confirms published estimates based on vegetation reestablishment continuous disturbance of the basin however may extend the recovery time for the whole basin well beyond 20 years

sediment erosion dynamics of a gullied debris slide a medium term record medium term post event sediment flux investigations are rare for headwater catchments and particularly sparse for gullied hillslope failures repeat field observation ground photography and cross section measurements of a debris slide scar at the wet swine gill headwater catchment 0 65 km2 in the english lake district uk provide evidence of erosion and deposition dynamics over the medium term 2002 2014 these data are compared to site topographic and meteorological conditions to evaluate potential process response linkages rill and gully erosion networks establish soon after the slide failure 1 february 2002 thereafter gully enlargement proceeds rapidly first by vertical downcutting prior to lateral expansion and gully wall angle decline changes in cross sectional width depth and area 2002 2013 are characterised by statistically significant p 0 05 negative exponential growth models r2 width 0 88 0 97 depth 0 71 0 86 area 0 87 0 93 gully walls were dominated by erosion but the gully bed was characterised by episodic sediment production storage and transfer often leading to temporary deposition specific erosion rates on the gully wall exceeded those on the adjacent slide scar by up to 764 maximum values wall 0 0084 scar 0 0011 m2 m 1 d 1 upslope contributing runoff area and slope gradient are generally important for erosion although linear regression analysis demonstrates weak or insignificant relationships between meteorological conditions and gully scar sediment flux a general conceptual model of slide scar evolution integrating gully growth and capture summarises activity at this site however transferability to locations with terrain characteristics land management practices and climate conditions different to those existing in the uk uplands remains to be tested this investigation adds to growing appreciation of the complexities of sediment dynamics in headwater catchments and provides clear evidence for the potential of early management intervention to counter detrimental post failure sediment erosion which at this site would have been most effective up to 3 4 years following gully initiation

origin of the picrite blocks in the marginal border group of the skaergaard intrusion east greenland abstract new evidence shows that the picrite blocks in the margins of the skaergaard intrusion east greenland are gabbro contaminated xenoliths of ultramafic rock earlier studies suggested that the picrite blocks were cumulates formed in the marginal border group or in the hidden zone however there are no known occurrences of undisturbed picrite or ultramafic rocks in the skaergaard intrusion and an extensive hidden zone is not supported by geophysical data the picrite blocks are most abundant near a body of wehrlite in precambrian rocks near watkins fjord the wehrlite which has a composition and mineralogy similar to the most mafic of the picrite blocks lies structurally below the northern margin of the intrusion it is possible that the refractory precursors of picrite in the skaergaard intrusion may have been ultramafic xenoliths and are not representative of the earliest differentiated pan of the intrusion

reassessment of proterozoic granitoid ages in ghana on the basis of u pb zircon and monazite dating abstract the west african craton in ghana is of early proterozoic age and forms alternating volcanic belts and sedimentary basins made up of rocks of the birimian supergroup as well as younger conglomerates and quartzites of the tarkwaian group and extensive granitoid plutons no consensus exists on absolute and relative ages of plutons within belts and basins u pb geochronology of four different granitoid complexes indicates that contrary to long held views belt granitoid plutons ashanti belt 2172 2 ma sefwi belt 2179 2 ma are 60 to 90 ma older than basin plutons kumasi basin 2116 1 ma belt granitoid are approximately coeval with volcanic rocks of the birimian supergroup while basin plutons are late kinematic and postdate tarkwaian sedimentation the first high precision geochronological data for rocks from ghana i e the eastern part of the birimian domain on the west african craton presented here show that magmatism within this region occurred over a time span of at least 90 ma and provide further evidence that the period between 2 1 and 2 2 ga was one of important magmatism in west africa

long term modelling of landslides for different forest management practices long term effects of different forest management practices on landslide initiation and volume were analysed using a physically based slope stability model the watershed based model calculates the effects of multiple harvesting entries on slope stability by accounting for the cumulative impacts of a prior vegetation removal on a more recent removal related to vegetation root strength and tree surcharge four sequential clearcuts and partial cuts with variable rotation lengths were simulated with or without leave areas and with or without understorey vegetation in a subwatershed of carnation creek vancouver island british columbia the combined in nite slope and distributed hydrologic models used to calculate safety factor revealed that most of the simulated landslides were clustered within a 5 to 17 year period after initial harvesting in cases where suf cient time c 50 years lapsed prior to the next harvesting cycle partial cutting produced fewer landslides and reduced landslide volume by 1 4 to 1 6 fold compared to clearcutting approximately the same total landslide volume was produced when 100 per cent of the site was initially clearcut compared to harvesting 20 per cent of the area in successive 10 year intervals a similar nding was obtained for partial cutting vegetation leave areas were effective in reducing landsliding by 2 to 3 fold retaining vigorous understorey vegetation also reduced landslide volume by 3 8 to 4 8 fold the combined management strategies of partial cutting increasing rotation length provision of leave areas and retention of viable understorey vegetation offer the best alternative for minimizing landslide occurrence in managed forests copyright 2003 john wiley sons ltd

a comparison of landslide rates following helicopter and conventional cable based clear cut logging operations in the southwest coast mountains of british columbia abstract a comparison of landslide rates following helicopter and conventional cable based clear cut logging was carried out using results from two independent terrain attribute studies in the eldred and lois river watersheds in the southwest coast mountains of british columbia landslides initiating from directly within a road prism were excluded from the study in order to focus the comparison on landslides related primarily to conventional versus helicopter yarding methods a landslide rate of 0 02 landslides ha was observed in 162 terrain polygons logged by helicopter 8 years prior to this study landslide rates in 38 gullied polygons were 0 06 landslides ha no landslides were observed in 124 open slope polygons over a similar 8 year average period 0 03 landslides ha were observed in 142 cable yarded terrain polygons 0 06 and 0 02 landslides ha occurred in gullied and open slope polygons respectively t tests indicate that total landslide rates are not significantly different following helicopter and conventional logging however a dichotomy exists between gullied and open slope terrain polygons landslide rates are not significantly different in gullied terrain but are significantly higher on open slopes following conventional cable logging consequently landslides appear to have a greater potential to occur in open slope terrain following conventional logging but differences in gullied polygons are less likely increased post logging landslide rates in conventionally logged open slopes are more likely the result of undetected road related drainage changes than differences between helicopter and conventional yarding related ground disturbance

generation and polybaric differentiation of east greenland early tertiary flood basalts major element trace element isotope and petrographic studies of magma diverentiation mantle melting the basal volcanics in the kangerdlugssuaq fjord region of the east greenland margin provide constraints on the generation and subsequent diverentiation and contamination histories of magmas during the early stage of continental rifting creating the north atlantic ocean basin most primitive lavas of the succession are introduction shown to have accumulated olivine corrections for crystal ac the distinctive geochemical features of continental flood cumulation yield estimates for erupted primitive liquids with mgo basalts cfbs are strongly controlled by the composition contents between 9 and 13 wt the occurrence of suspended and structure of the continental lithosphere and underfo88 olivine phenocrysts further requires the existence of parental lying mantle significant controversy remains concerning magmas with mgo contents up to 17 wt and feo contents up the balance of contributions from the lithosphere and to 14 wt quantitative modeling of fractionation indicates the mantle and the mechanisms by which the various that kangerdlugssuaq magmas primarily diverentiated at moderate source components contribute to basalt petrogenesis pressures 8 kbar to form dunitic and wehrlitic cumulates at how are basalt compositions influenced by generation depths of 25 km evolved east greenland flood basalts from the in anomalous regions in the deep mantle plumes by scoresby sund region record a more complex fractionation history interaction between rising magmas and the continental involving olivine clinopyroxene fractionation in the lower crust lithospheric mantle and by contamination with conas found for the lower basalts followed by olivine plagioclase tinental crust how are the diverentiation con clinopyroxene fractionation at shallow crustal levels cor tamination magma mixing and storage histories of cfbs relations between sio2 incompatible elements and sr nd isotopic controlled by the structure of the continental lithosphere ratios for the lower basalts are consistent with bulk assimilation and how do the thermal and chemical features of the of up to 15 20 archean leucogneiss with unradiogenic sr and mantle and the extensional history of the continental nd isotopic ratios characteristic of lewisian type lower crust lithosphere avect mantle melting and compositions of comparisons between inferred magma types for lower basalts and primary liquids estimated primary liquids from elsewhere in the north atlantic these questions are best addressed in the context of show complex relationships among feo mgo tio2 contents a geologically and geochemically well constrained cfb and cao al2o3 ratios that relate to regional and temporal changes province such as the north atlantic tertiary province in mantle temperatures lithospheric thickness and involvement of separation of east greenland from northern europe in at least two end member mantle sources we postulate that the the early tertiary at 60 myr ago was accompanied by lower basalts of east greenland were derived from iron poor voluminous volcanic activity the blosseville coast of mantle depleted by prior melt extraction and distinct from morb east greenland extending from kangerdlugssuaq fjord source mantle that was enriched in tio2 and lrees by a to scoresby sund fig 1 contains spectacularly exposed metasomatic event shortly before early tertiary magmatism we sections of lavas these sections begin at the basal contact associate this depleted mantle source with the ancestral iceland of the lavas with underlying cretaceous tertiary sediments and archean basement and continue to the plume anomaly

redwoods restoration and implications for carbon budgets abstract the coast redwoods sequoia sempervirens of california have several unique characteristics that influence interactions between vegetation and geomorphic processes case studies using a combination of in channel wood surveys and an air photo inventory of landslides illustrate current conditions in a redwood dominated watershed undergoing restoration work and the influence of wood loading and landslides on the carbon budget redwood trees have extremely large biomass trunk wood volumes of 700 to 1000 m3 and are very decay resistant consequently they have a large and persistent influence on in channel wood loading large wood surveys indicate high wood loading in streams in uncut forests 0 3 0 5 m3 m2 of channel but also show that high wood loading can persist in logged basin with unlogged riparian buffers because of the slow decay of fallen redwoods through a watershed restoration program redwood national park increases in channel wood loading in low order streams but the effectiveness of this technique has not yet been tested by a large flood another unique characteristic of redwood is its ability to resprout from basal burls after cutting so that root strength may not decline as sharply following logging as in other types of forests an air photo inventory of landslides following a large storm in 1997 indicated 1 that in the redwood creek watershed the volume of material displaced by landslides in harvested areas was not related to the time elapsed since logging suggesting that the loss of root strength was not a decisive factor in landslide initiation 2 landslide production on decommissioned logging roads was half that of untreated roads and 3 landslides removed an estimated 28 mg of organic carbon km2 from hillslopes the carbon budget of a redwood dominated catchment is dominated by the vegetative component but is also influenced by the extent of mass movement erosion control work and in channel storage of wood

late archean granitoid hosted lode gold deposits yilgarn craton western australia deposit characteristics crustal architecture and implications for ore genesis granitoid hosted lode gold deposits constitute a sub group of late archean lode gold deposits in the yilgarn craton of western australia they share a number of common characteristics including 1 a strong structural control on a variety of scales 2 in most instances the presence of mineralisation in adjacent supracrustal sequence 3 wallrock alteration and vein assemblages consistent with the addition of sio2 k2o co2 s na2o but dependent on the p t conditions of the host environment and ore fluid 4 a metal association comprising au ag as bi te w mo and low concentrations of cu pb and zn and 5 deposition from a low moderate salinity near neutral h2o co2 ch4 fluid over a temperature and pressure range from 250 to 600 c and 1 to 4 kbar which corresponds to a range of crustal environments from lower greenschist to upper amphibolite facies these characteristics suggest that the granitoid hosted lode gold deposits represent a coherent genetic group that is equivalent to the more abundant greenstone hosted lode gold deposits of the craton in combination lode gold deposits irrespective of their host rocks and host terrane formed over a range of crustal levels and developed late in the tectonic sequence of the craton granitoids which host lode gold mineralisation are older than the inferred age of mineralisation by at least 10 million years and in combination with thermodynamic and isotope studies indicate that the host granitoids are not the dominant source of the ore fluid however the host granitoids do provide a structural and to a lesser extent chemical trap for gold bearing fluids in combination trace element and isotope studies of greenstone and granitoid hosted deposits suggest that the ore fluid originated from a deep mid to lower crustal source and at least interacted with granitic rocks at some stage the ore fluid composition is quite constant over the range of crustal levels from deep to shallow implying that the extent of modification by interaction with fluid conduit rocks is variable but not substantial

the skaergaard layered series part iv reaction transport simulations of foundered blocks during the middle stages of crystallization of the skaergaard layered series large numbers of blocks became detached from the upper border series and settled into the mush of crystals on the floor it has been recognized for some time that these blocks now have compositions and textures that differ markedly from those of the units from which they came they tend to be more plagioclase rich and seem to have lost mafic components to the surrounding gabbro numerical simulations coupling crystallization melting and heat and mass transfer for a multicomponent system show how the blocks reacted with the mush in which they were emplaced enhanced cooling and crystallization of a compositionally stratified mush adjacent to the blocks resulted in patterns of melt compositions similar to those of layering around the blocks volume changes during crystallization and melting induced convection of the interstitial melt leading to changes in the bulk compositions of the blocks and the surrounding mush inhomogeneities such as inclusions are likely to facilitate the onset of compositional convection in a chemically stratified solidification zone

xenoliths of gneisses and the conformable clot like granophyres in the marginal border group skaergaard intrusion east greenland results of this research and the earlier work of wager and his colleagues indicate that contamination influenced the overall character of the marginal border group of the skaergaard intrusion precambrian gneisses were a major source of contamination and are identifiable as xenoliths in the marginal border a variety of other xenoliths occur with a wide compositional range

sources of suspended sediment within a tropical catchment recovering from selective logging quantification of the source of suspended sediments generated by selective forestry activities is central to the development of sustainable forestry guidelines this assessment is hampered by a dearth of available studies particularly from the tropics this study involved the monitoring at 10 s intervals of surface discharge and turbidity from 15 contributory areas of a 44 ha catchment the catchment is located within lowland dipterocarp rain forest on borneo island in a region recovering from the first episode of selective timber removal that took place some 5 years previously both the within storm dynamics of the sediment flux and the time integrated sediment yields were analysed to link the source landforms to the catchment behaviour a 10 year rainfall event of 167 mm occurred during the monitoring period and triggered a debris slide and several log culvert collapses along the area s main timber haulage road the sampling design captured this event s dynamics and allowed lumped catchment response to be traced to the new landforms during the 1 day period of the 10 year event some 33 t of suspended sediment were transported from one debris slide comprising a significant proportion of the 105 t discharging from the whole catchment which itself constituted 40 of the annual yield of 592 t km 2 the contributory areas with only ephemeral waterflows including former haulage roads and tracks generated relatively little sediment during this 10 year event or in other storms this work suggests that though some sediment sources recover from the impacts of forest road construction and harvesting collapse of roadfill materials or more local log culvert failure persists for several years after harvesting sustainable forestry guidelines that do not focus on ameliorating these persistent instabilities may not significantly mitigate the geomorphic impacts of conventional selective harvesting copyright 2004 john wiley sons ltd

the impacts of logging on landslide activity at clayoquot sound british columbia abstract the objective of this study was to investigate the impacts of logging on landslide activity in clayoquot sound on the west coast of vancouver island british columbia a total of 1004 landslides were documented in order to test the hypothesis that areas affected by logging activities show different density frequency and magnitude characteristics of landsliding than areas unaffected by logging the frequency of landslides in logged terrain was found to be nine times higher than in undisturbed forest an exponential increase in landslide frequency within the area logged was observed on a large watershed scale failures in logged terrain occur on gentler slopes than in natural terrain partly because fewer slopes steeper than 40 have been logged debris slides and debris flows are the most frequently occurring mass movements initiating mostly from road fill failures and from within cutblocks most landslides initiated on se facing slopes with the highest landslide frequency near the coast and diminishing exponentially further inland this pattern of activity most likely reflects the greater impact of severe storms arriving from the pacific with winds dominating from the southeast concave and straight slopes are most susceptible to landslide initiation a preliminary examination of geologic control on the frequency of landslides suggests that the quatsino formation the island plutonic suite and the sicker group are significantly above the average rate further work is needed to identify and quantify factors confounding the trends and correlations identified in this overview study results obtained in this study will be used to implement changes in forest management

logging effects on sediment flux observed in a pollen based record of overbank deposition in a northern california catchment a palynological approach was used to estimate overbank deposition rates in a forested catchment affected by logging the palynological approach uses downcore variations in total fossil pollen and fossil pollen assemblage to calculate rates of overbank deposition and has a distinct advantage over radioisotopic approaches in that it is not limited by radioactive decay using this approach we determined that overbank deposition rates increased over 400 per cent within years of logging events and that the increased rates persisted for less than 4 years after logging induced deposition peaked overbank deposition decreased over 60 per cent relative to the pre logging background values the decreased deposition rates persisted for over 40 years the immediate effect of logging in this catchment was to induce mass wasting events in hollows that produced rapidly travelling sediment pulses in the subsequent recovery period reduced sediment loading occurred as a result of a reduction in the volume of sediment available for transport the reduction in sediment load led to a reduction in overbank deposition rates until subsequent logging disturbances destabilized and emptied other hollows

seasonal changes in the sediment flux on steep hillslopes in a humid diurnal frost environment mountain hillslopes are generally shaped by a combination of various types of sediment transport processes e g surface erosion soil creep and dry ravel which can occur simultaneously in the same area since sediment transport is generally affected by multiple microclimatic factors such as heavy rainfall and changes in ground temperature the types of predominant sediment transport processes vary by season we conducted field observations in the southern japanese alps in the period from 2009 to 2013 using sediment traps and time lapse cameras to investigate the seasonal changes in the type and flux of hillslope sediment transport on steep mountains in which both rainfall and diurnal freeze thaw triggered sediment transport in winter and early spring sediment transport via diurnal freeze thaw soil creep and dry ravel was highly active whereas rainfall induced soil creep and selective transport by overland flow were active in summer and autumn when precipitation is abundant average sediment flux of 0 033 and 0 074 kg m 1 day 1 respectively sediment flux was spatially variable and was affected by the form of the slope sediment flux on the concave slope was higher than on the ridge shaped slope during both freeze thaw and rainfall periods sediment flux on an old landslide exceeded that in second growth forest regardless of the slope shape temporal changes in the sediment flux were not completely synchronized among monitoring plots and were affected by slope shape grain size and episodic sediment supply events such as release of sediment from woody debris copyright 2016 john wiley sons ltd

initiation and runout characteristics of debris flow surges in ohya landslide scar japan abstract the characteristics of debris flows e g velocity discharge kinematic energy are highly dependent on surges incurring abrupt changes to flow height velocity and boulder concentration therefore understanding the initiation and runout characteristics of surges is essential when planning debris flow mitigation monitoring performed using 10 time lapse cameras tlcs in ohya landslide central japan where debris flows occur frequently due to mobilization of storage i e talus cone and channel deposits allowed us to obtain data on a series of surge processes from initiation to termination which occurred during each debris flow event we also analyzed temporal changes in the spatial distribution of storage in the debris flow initiation zone associated with sediment supply from hillslopes and evacuation of sediment by the occurrence of debris flows through periodic measurements of topography using unmanned aerial vehicles uavs debris flow surges were mainly induced by repetitive mass movement of storage through the erosion of channel deposits by overland flow sliding of channel deposits and sediment and water supply from channel banks and tributaries development of a spontaneous wave on the flow surface was not an important formation process of surges in the ohya landslide many debris flow surges initiated at channel sections with deep storage 2 m in depth located

early proterozoic crustal evolution in the birimian of ghana constraints from geochronology and isotope geochemistry abstract representative suites of ghanaian granitoids metavolcanics and metasediments were selected from birimian rock units for rb sr pb pb and sm nd analyses isotopic data on the igneous rocks provide evidence for a major early proterozoic crust forming episode which took place over a maximum time interval from 2 3 to 2 0 ga by a differention from a depleted mantle source there is little evidence for the involvement of significantly older e g archaean crust in the genesis of the igneous rock units the only exception so far found is the winneba granitoid which appears to contain a magmatic contribution from presumably underlying archaean basement sm nd model ages indicates that birimian sediments were derived from adjacent penecontemporaneous volcanic belts the birimian of ghana forms part of a major proterozoic eburnean episode of juvenile crustal accretion which has been recognised in the surrounding areas of mauretania senegal ivory coast burkina faso mali and niger where it has been dated at 2 1 2 2 ga abouchami et al the birimian terranes bridge a major gap in mantle activity and associated crustal evolution for a period considered as quiescent on other continents

small slope tilts caused by meteorological effects and vital processes of trees on a wooded slope in hidegviz valley hungary abstract long term measurements were carried out to investigate the relationship between ground tilts and variations of meteorological temperature precipitation and hydrological soil moisture content parameters in the area of the sopron mountains on a wooded slope of the hidegviz valley hungary the connection between surface tilts and the vital processes of the trees was also studied on the basis of the reference evapotranspiration calculated for the study area long and short term variations were separated a long term ground temperature change of 1 c caused a 4 rad tilt in the se direction short term temperature effects can be neglected the fluctuation of temperature around the freezing point caused tilts of about 10 rad c 1 the soil water content variation had the largest effect on the ground tilt 0 5 rad mm 1 its contribution to the total ground tilt in the investigated period was about 70 rad 65 of the total tilt of 107 rad toward the sse the contribution of the wind speed to the ground tilt was about 20 rad m s 1 toward the sse depending on the water content of the soil the wind did not cause a permanent ground tilt the magnitude of the daily tilt variations in the active growing period of trees from march to october is 1 2 rad while in the dormant period with no canopy the tilt variations were less than 0 4 rad the admittances between the evapotranspiration and the ground tilts were 0 3 0 5 rad mm 1 and 0 1 0 2 rad mm 1 in the active and dormant period of the trees respectively these small effects superimposed on each other can significantly contribute to slope failures the results of this study provide information which can be useful in the modelling of landslide movements and for the mitigation of landslide hazards

metamorphism of the pelitic rocks of the snyder group in the contact aureole of the kiglapait layered intrusion labrador effects of buffering partial pressures of water the petrography and mineral chemistries of the aphebian snyder group pelitic rocks in the contact aureole of the kiglapait layered intrusion labrador reveal a rapid increase in metamorphic grade o

origin of the transgressive granophyres from the layered series of the skaergaard intrusion east greenland abstract the transgressive granophyres are a swarm of silicic dikes and sills in the layered series of the skaergaard intrusion that range in composition from ferrodiorites to granites although originally thought to be derived by differentiation of skaergaard magma accumulated evidence indicates that the origin of these granophyres is more complex and involves contributions from melted country rocks in the present study it is shown that field relations are inconsistent with any genetic relationship between the transgressive granophyres from the layered series and differentiated skaergaard magma although new sr isotope analyses confirm that these granophyres are at least partly derived by fusion of archean country rock field relations preclude derivation of this crustal component from partially melted gneissic xenoliths from the skaergaard magma chamber or from melting along the contact between the gneisses and the skaergaard pluton major and trace element compositions together with sr isotope ratios indicate that the transgressive granophyres from the layered series represent a cogenetic suite of magmas related to each other primarily by a closed system process such as crystal fractionation and that the parental magma that gave rise to these granophyres was formed beneath the skaergaard intrusion by contamination of differentiated post skaergaard mafic magmas with partially fused archean crust

evolution of a large landslide in the high himalaya of central nepal during the last half century episodic and catastrophic landslides are considered to be one of the main sources of sediment in the steep mountainous landscapes of the himalayas however the evolution of a single landslide through time and its contribution to erosional processes remain poorly constrained in this study we focus on a single large 0 5 km2 landslide in a small catchment on the southern flank of the annapurnas in nepal the khudi valley in order to quantify its importance in the overall erosion of this steep himalayan catchment the evolution of the saituti landslide has been continuously monitored by remote sensing for the past 46 years during that period the saituti landslide displayed sustained activity such that the area of the landslide scar increased by a factor of 4 this retrogressive failure a consequence of several sporadic flank and crown collapses has not been continuous rather acceleration phases have alternated with more quiescent periods simultaneously the upper edge moved upward by 900 m based on field evidence from recent activity such as scarps and open tension cracks above the landslide and on an analysis of slope angles at least the next 500 m is expected to fail volume losses within the landslide were estimated from differences between digital elevation models dems and from changes in landslide area using a calibrated power law relationship between landslide area and volume corresponding landslide induced erosion rates at the scale of the whole khudi catchment were found to be 2 6 0 9 mm y for the past half century those rates are similar to denudation rates obtained from sediment load measurements between 1999 and 2004 those results along with the lack of other major landslides in the valley for the last 46 years suggest that the saituti landslide plays a dominant role in the modern erosion of the high himalayan khudi catchment for the last years and possibly for the past few decades we propose that continuous and sustained activity of a few major landslides over the past few decades might represent a significant contribution to the erosion of the high himalayan range this long lasting landslide induced erosion should be taken into account when interpreting suspended load measurements results from provenance analysis or cosmogenic nuclides in river sand such processes should also be included in landscape evolution models when annual to secular problems are explored

the differentiation of the skaergaard intrusion mcbirney and naslund have missed the two central points that we reiterate for clarity first the composition of the cotectic cumulate extract for the lzc best estimated from the average composition of adcumulate rocks had a substantially lower silica content than any conceivable basaltic liquid so silica enrichment is unavoidable this is true of all the dyke compositions reported by brooks and nielsen even the anomalous rock e with sio2 46 second it is the normal behaviour of tholeiite basaltic magma to produce increasingly iron rich cumulate extracts with little change in silica until feti oxide precipitation occurs when silica enrichment and compositional divergence begins such divergence between equivalent cumulate plutonic and fractionated volcanic rocks hads been widely documented skaergaard magmas do have some uncommon features however similar assemblages exist in volcanic rocks as in the andesitic to rhyolitic glasses of the loch ba ring dyke mull sparks 1988 it is also a basic principle that elements enriched in cumulate rocks often become depleted in the corresponding liquids iron enrichment in the skaergaard cumulates is complementary to iron depletion in liquids

recognition classification and mechanical description of debris flows abstract various types of flow or mass movement involving water and sediments occur on steep slopes in mountainous areas among them debris flows are peculiar events during which a large volume of a highly concentrated viscous water debris mixture flows through a stream channel throughout the world these phenomena cause considerable damage but remain poorly understood although a basic knowledge is already available concerning their recognition and propagation firstly a synthesis of the useful practical criteria of recognition is proposed debris flows must be seen as intermediate phenomena between hyperconcentrated flows intense bed load transport and landslides separated from them by sharp transitions of some characteristics celerity deposit nature and flow type two parameters solid fraction and material type thought to be appropriate for a sound and practical classification are brought out and the corresponding complete classification of flow and mass movements in mountain areas is presented two extreme debris flow types are thus distinguished muddy debris flows and granular debris flows a critical review of recent advances in debris flow dynamic is then proposed it is pointed out that adequate work must be carried out in the field of non newtonian fluid mechanics in particular one fundamental rheological property of debris flow materials is the yield stress which explains thick deposits on steep slopes and can be inferred from field measurements furthermore it can be used to estimate viscous dissipation within the bulk during flow relevant models predicting muddy debris flow dynamics are already available whereas further progress is needed concerning granular flows

forest clearing and regional landsliding the influence of forest clearing on landsliding is central to longstanding concern over the effects of timber harvesting on slope stability here we document a strong topographic control on shallow landsliding by combining unique ground based landslide surveys in an intensively monitored study area with digital terrain modeling using high resolution laser altimetry and a coarser resolution regional study of 3224 landslides as predicted by our digital terrain based model landslides occur disproportionately in steep convergent topography in terrain predicted to be at low risk of slope failure a random model performs equally well to our mechanism based model our monitoring shows that storms with 24 hr rainfall recurrence intervals of less than 4 yr triggered landslides in the decade after forest clearing and that conventional monitoring programs can substantially underestimate the effects of forest clearing our regional analysis further substantiates that forest clearing dramatically accelerates shallow landsliding in steep terrain typical of the pacific northwest

age constraints on gold mineralization and paleoproterozoic crustal evolution in the ashanti belt of southern ghana abstract u pb isotopic dating in the region of the ashanti belt in ghana has been carried out to improve understanding of crustal evolution and gold mineralization in this paleoproterozoic terrane a u pb zircon age of ca 2174 2 ma for a belt type granitoid from sekondi accords with previous ages on belt type plutons in ghana but metamorphic titanite within this granitoid gives an age of 2092 3 ma coeval with intrusion of the late basin type granitoids the within belt granitoid at banso village has an age close to 2097 3 ma which falls into the age range typical for basin type granitoids 2116 2088 ma these results indicate that widespread plutonism in the birimian sedimentary basins also produced magmatic and metamorphic effects within the volcanic belts most dated detrital zircons from birimian metasediment samples at the ashanti gold mine agree in age at 2155 2 ma with others that are slightly older this gives a maximum estimate for the depositional age of the sediments and for gold mineralization at the ashanti gold mine hydrothermally altered and auriferous granitoid plutons along the western flank of the ashanti belt at anyankyerim nhyiaso yaomensakrom and esuajah ayanfuri all have intrusion ages within error of 2105 2 ma this is also the age of metamorphic titanite in an unmineralized basin type granitoid at kwapia rutiles from the hydrothermally altered yaomensakrom and the mineralized esuajah ayanfuri granitoid were dated at 2098 7 and 2086 4 ma respectively and probably provide minimum ages on gold mineralization these data indicate a close temporal association among auriferous granitoid plutons near the western margin of the ashanti belt at 2105 ma gold mineralization may be only slightly younger than magmatic emplacement of the plutons granitic plutonism in the sedimentary basins metamorphism and hydrothermal gold mineralization in southern ghana are all part of a major crust formation event the eburnean orogeny that can be constrained to the time range 2120 2080 ma

comparison of gis based gullying susceptibility mapping using bivariate and multivariate statistics northern calabria south italy abstract this paper presents gis aided procedures for the evaluation of gullying susceptibility on a statistical basis field surveys and air photo interpretation allowed us to identify gullies geology and land use while some predisposing factors were derived from a 7 5 m cell size dem in order to investigate the role of each instability factor in controlling the spatial distribution of gullies we implemented four models that differ in the types of method bivariate vs multivariate training set sampling polygon or point based and variables continuous or categorical the models were applied to the turbolo river catchment a tributary of the crati river northern calabria italy the susceptibility values were classified into five categories model performance was evaluated using prediction rate curves and by comparing the proportion of each susceptibility class with gully distribution in the validation set although all models showed relatively good performances the bivariate method overestimated the extent of the high susceptibility classes the multivariate logistic regression model using continuous variables was found to be the best model in predicting gullying susceptibility of the study area the area classified as stable increased with dem cell size meaning that a reasonably fine dem should be used

gold mineralisation at the lady bountiful mine western australia an example of a granitoid hosted archaean lode gold deposit the lady bountiful granitoid hosted lode gold deposit located in the mid greenschist facies metamorphosed ora banda greenstone sequence is hosted predominantly by the late tectonic liberty granodiorite gold mineralisation is localised along quartz veined sinistral brittle fault zone s that transect the boundary between the liberty granodiorite and mt pleasant sill quartz vein textures indicate two stages of a single gold related vein development event with high grade gold mineralisation restricted to the second stage ore minerals include pyrite chalcopyrite pyrrhotite galena sphalerite au ag bi pb tellurides and native gold fluid infitration has resulted in narrow 1 m bleached wallrock alteration envelopes to the fault zones comprising albite k mica chlorite calcite rutile assemblages temperature pressure conditions varied from stage i 300 50 c 2 kbar to stage ii 250 50 c 0 5 to 2 kbar with the hydrothermal fluid in both stages characterised by x co2 0 15 and moderate salinity 1 28 m nacl intermittent phase separation of stage ii mineralising fluids initiated by pressure fluctuations in dilational sites and or fluid dominated fluid wallrock interaction are invoked as the dominant depositional mechanisms the granitoid hosted lady bountiful lode gold deposit shares many features with other granitoid hosted lode gold deposits in the yilgarn craton and the superior province granitoid hosted lode gold deposits such as the lady bountiful deposit provide additional evidence that the dominant control on the localisation of gold mineralisation within a granitoid host is structure with competency contrasts playing a significant role furthermore the hydrothermal wallrock alteraction and orefluid chemistry characteristics of the granitoid hosted lode gold deposits are comparable to those established for greenstone hosted lode gold mineralisation

landslide volumes and landslide mobilization rates in umbria central italy abstract a catalogue of 677 landslides of the slide type was selected from a global database of geometrical measurements of individual landslides including landslide area al and volume vl the measurements were used to establish an empirical relationship to link al in m2 to vl in m3 the relationship takes the form of a power law with a scaling exponent 1 450 covers eight orders of magnitude of al and twelve orders of magnitude of vl and is in general agreement with existing relationships published in the literature the reduced scatter of the experiential data around the dependency line and the fact that the considered landslides occurred in multiple physiographic and climatic environments and were caused by different triggers indicate that the relationship between vl and al is largely independent of the physiographical setting the new relationship was used to determine the volume of individual landslides of the slide type in the collazzone area central italy a 78 9 km2 area for which a multi temporal landslide inventory covering the 69 year period from 1937 to 2005 is available in the observation period the total volume of landslide material was vlt 4 78 107 m3 corresponding to an average rate of landslide mobilization l 8 8 mm yr 1 exploiting the temporal information in the landslide inventory the volume of material produced during different periods by new and reactivated landslides was singled out the wet period from 1937 to 1941 was recognized as an episode of accelerated landslide production during this 5 year period approximately 45 of the total landslide material inventoried in the collazzone area was produced corresponding to an average rate of landslide mobilization l 54 mm yr 1 six times higher than the long term rate the volume of landslide material in an event or period was used as a proxy for the magnitude of the event or period defined as the logarithm base 10 of the total landslide volume produced during the event or period with this respect the new relationship to link al and vl is a starting point for the adoption of a quantitative process based landslide magnitude scale for landslide events

assessment of soil erosion sensitivity and post timber harvesting erosion response in a mountain environment of central italy article i nfo this study aimed to assess the effects of forest management on the occurrence of accelerated soil erosion by water the study site is located in a mountainous area of the italian central apennines here forest harvesting is a widespread forestry activity and is mainly performed on the moderate to steep slopes of the highlands through modeling operations based on data on soil properties and direct monitoring of changes in the post forest harvestingsoilsurfacelevelatthehillslope scale we show thattheobserved site became pronetosoilero sion after human intervention indeed the measured mean soil erosion rate of 49 t ha 1 yr 1 for the harvested watershed is about 21 times higher than the rate measured in its neighboring undisturbed forested watershed 2 3 t ha 1 yr 1 the erosive response is greatly aggravated by exposing the just harvested forest with very limited herbaceous plant cover to the aggressive attack of the heaviest annual rainfall without adopting any conservation practices the erosivity of the storms during the first four months of field measurements was 1571 mj mm h 1 ha 1

dynamic earth system and ecological controls of rainfall initiated landslides abstract rainfall initiated landslides continue to inflict damages and loss of life throughout the world processes and mechanisms revealed from hydrological geomorphic geotechnical pedological geological hydrochemical and biological investigations have advanced our understanding of these effects on slope stability however the interactions amongst these processes and attributes as they affect the initiation and propagation of landslides are not as well understood too often landslide studies are conducted from only one or at most two of these perspectives moreover while precipitation and hydrology are recognized as dynamic influences the earth system and ecological effects are often assumed to be static we assess the interplay of these processes related to landslides triggered by positive pore water accretion and loss of soil suction each of these conditions arguably requires a different view on the processes that cause slope failure and predictive approaches this review starts from the perspective of dynamic adapting earth and ecological systems and discusses how these attributes relate to landslide initiation mode location and timing specifically the role that large and small scale preferential flow plays in both contributing to and mitigating instability is elucidated including effects of bedrock exfiltration we also examine how and under what conditions these pathways manifest in different soils lithology and landforms the multiple effects of rhizosphere processes on slope stability are discussed including root reinforcement evaporation from canopies and litter layers transpiration and the role of root structure affecting preferential flow paths rainfall initiated landslides involve highly dynamic hydrologic earth surface and ecological processes that persist over a range of spatial and temporal scales however guidance for overcoming these challenges has been elusive a conceptual framework is presented to shed light on these dynamic and interactive processes that should lend insights into why and when certain slopes fail during storms while other seemingly similar slopes do not fail such advances will benefit landslide hazard assessments and disaster responsiveness protocols

landslide inventory in a rugged forested watershed a comparison between air photo and field survey data abstract landslide inventories are routinely compiled by means of aerial photo interpretation api when examining photo pairs the forest canopy notably in old growth forest hides a population of not visible landslides in the present study we attempt to estimate how important is the contribution of landslides not detectable from aerial photographs to the global mass of sediment production from mass failures on forested terrain of the capilano basin coastal british columbia api was coupled with intensive fieldwork for identification and measurement of all landslides a 30 year framework was adopted we show that not visible landslides can represent up to 85 of the total number of failures and account for 30 of the volume of debris mobilised such percentages display high sub basin variability with rates of sediment production varying by one order of magnitude between two sub basins of the study area this is explained qualitatively by gis based analysis of slope frequency distributions drainage density and spatial distribution of surficial materials such observations find further support in the definitions of transport limited and supply limited basins as a practical consideration to land managers we envisage that supplementary fieldwork for landslide identification is mandatory in transport limited systems only fieldwork has demonstrated that gully related failures have a greater importance than one could expect from api

average landslide erosion rate at the watershed scale in southern taiwan estimated from magnitude and frequency of rainfall abstract this study calculated the long term average landslide erosion rate in the kaoping river watershed in southern taiwan and investigated the relative importance of extreme rainfall events on landslide erosion the method followed three steps first calculating landslide volumes for 10 rainfall events from a multi temporal event based landslide inventory second estimating the frequency of landslide generating rainfall by using hydrologic frequency analyses and third combining the two sets of data to estimate the average landslide erosion rate results of the study showed that the average landslide erosion rate is 2 65 5 17 mm yr 1 corresponding well to rates reported in other studies using other methods the study also found that extreme intensive rainfall events play a more important role on landslide erosion than frequent moderate rainfall events extreme rainfall maximum 24 h rainfall 600 mm contributes 64 79 of the average landslide erosion rate moreover the natural variation of landslide erosion magnitudes is extremely large and can cause significant uncertainty in estimating the landslide erosion rate from total landslide volume this study found 1 2 mm yr 1 of uncertainty based on simulation results involving a hypothetical 100 year landslide inventory in summary this study demonstrates the importance of extreme rainfall events on landslide erosion and the method proposed in this study is capable of calculating a reliable estimate of average landslide erosion rate in areas with insufficient landslide records

distribution of landslides caused by heavy rainfall events and an earthquake in northern aso volcano japan from 1955 to 2016 abstract a new landslide cannot form until the soil has recovered to the critical depth for the recurrence of a landslide through the weathering of bedrock and soil transportation from adjacent areas in volcanic areas with tephra deposits landslides expose tephra and not bedrock therefore the immunity of landslides in volcanic areas may be different from that of landslides in non volcanic areas herein we developed landslide inventory maps lims for 6 periods during 1955 2016 using aerial photographs and digital elevation models in northern aso volcano in this area landslides were found to continuously occur due to rainfall events and a large earthquake using the 6 lims we examined the terrain attributes i e slope angle slope aspect and normalized distance to ridge and the overlap of landslides among the terrain attributes slope angle was a dominant factor affecting the occurrence of landslides caused by both rainfall events and an earthquake the total landslide areal density in 2016 was 50 for a slope angle of 35 45 2 atypical events a rainfall in july 2012 and an earthquake in april 2016 caused landslides to occur on slopes that were relatively resistant to landslides by typical amounts of rainfall resulting in high landslide density in 2016 the intensity of rainfall for an event in july 2012 was considerably higher than that for other rainfall events the type of landslides caused by an earthquake in april 2016 was different from that of landslides caused by rainfall the depths of some landslides caused by this earthquake were deeper than those of landslides caused by the rainfall in july 2012 the overlap ratio was

runoff process on a steep forested slope abstract three slope units are defined by combining nine basic slope types a convergent slope unit is called a zero order basin because it combines a slope and a stream field measurements of the runoff process of stormflow on pliocene slopes are presented pipe flow and saturated overland flow play an important part on convergent colluvial slope units surface soils significantly influence saturated throughflow on creeping middle slopes the depth of weathering has a major effect on initial moisture storage for residual and creeping slopes a subsurface storm flow pattern on a typical pliocene slope is reconstructed based on the field measurements

influence of topography and volume on mobility of loess slides within different slip surfaces mobility of loess slides has been evaluated using an empirical approach based on a detailed field investigation and remote sensing image interpretation for all the loess slides the affected area increases with increasing loess slides volume from the statistical analysis it is seen that the travel distance has an increasing trend while the coefficient of friction has a decreasing trend with the increase in landslide volume landslide volume determine its travel distance and coefficient of friction that can be shown with a regression equation having simple power law form which indicates that the mobility of loess slides increases with increasing volumes by analogy the greater the energy of the sliding loess mass the stronger is the mobility of loess slide a plot of the travel distance of loess slide versus fall height shows a significant positive power law correlation indicating the increase in mobility of loess slide with fall height the negative power law correlation observed between the travel distance and slope inclination implies that the mobility decreases with the increase of slope inclination three datasets of loess slides characterized by different slip surfaces were distinguished the red clay contact landslides have the strong mobility than landslides in loess and bedrock contact

biographical sketch of a giant deciphering recent debris flow dynamics from the ohya landslide body japanese alps abstract debris flow frequency discharge and travel distance are highly catchment dependent and typically controlled by topography hydrological conditions and sediment supply as a consequence detailed and case specific investigations are needed to decipher debris flow histories in order to improve hazard mitigation this study documents past ca 10 years debris flow occurrences originating from the ohya landslide central japan by using a large set of methods including field monitoring repeat airborne lidar orthophoto interpretation and tree ring reconstructions we demonstrate that the different approaches generally agree on the occurrence of debris flows but that mismatches may exist when it comes to the assessment of areas affected by individual events these differences may even exceed the usual errors in precision inherent to each of the methods used in the present case high resolution orthophoto interpretation tends to underestimate areas affected by debris flows especially in the vertical direction in the absence of lateral movement of the channel bed and as a result of shade and areas under trees on the other hand we realize that lidar data cannot necessarily be used to distinguish local changes in topography from noise tree ring analyses can help to improve the temporal resolution of the analysis but may have limitations when it comes to the definition of areas affected by an event because of the point type nature of data we conclude that the best and most complete results are obtained by combining multiple methods to improve the spatial and temporal resolution of past debris flows and to delimit areas affected by individual events

debris flow initiation and sediment recharge in gullies landslides that enter gullied low order drainages can either initiate debris flow or stop depositing sediment in the channel this process is one of the most common ways that debris flows initiate but little attention to date has been paid to evaluating the factors that affect whether or not the initial landslide will become a debris flow or deposit sediment in the channel statistically significant parameters that determine whether slope failures become debris flows or act to recharge in channel sediment are channel gradient angle of entry of failure into the channel initial failure volume and the amount of in channel stored sediment steeper channels low angles of entry lower volumes of in channel sediment and larger initial failures were more likely to result in debris flows this study found that as the volume of in channel stored sediment increased the volume of initial failure required to initiate a debris flow also increased this result calls into question the simple supply limited model of cyclical debris recharge and debris flow in low order gullied drainages and suggests a negative feedback mechanism between debris accumulation and debris flow susceptibility

forest roads and geomorphic process interactions cascade range oregon a major flood in february 1996 triggered more than 100 geomorphic features affecting forest roads in a 181 km 2 study area in the western cascade range oregon eight types of features including mass movements and fluvial features were mapped measured and analysed using geographic information systems and sediment budgets for the road network although roads functioned as both production and depositional sites for mass movements and fluvial processes the net effect of roads was an increase in basin wide sediment production debris slides from mobilized road fills were the dominant process of sediment production from roads road related sedimentation features were concentrated in a portion of the study area that experienced a rain on snow event during the storm and was characterized by the oldest roads and steep slopes underlain by unstable highly weathered bedrock the downslope increase in frequency of features and volumes of sediment produced combined with the downslope increase in relative frequency of fluvial over mass wasting processes suggests that during an extreme storm event a road network may have major impacts on stream channels far removed from initiation sites overall this study indicated that the nature of geomorphic processes influenced by roads is strongly conditioned by road location and construction practices basin geology and storm characteristics published in 2001 by john wiley sons ltd

representing the landslide magnitude frequency relation capilano river basin british columbia we use magnitude frequency analysis as a statistical tool to quantify the erosion caused by landslides and debris ows using air photo and ground derived data we show that the departure from power law distribution customarily observed for small magnitude is an artefact of sampling de ciencies nonetheless the total distribution is not sensitive to the frequency of small slides and total erosion remains adequately represented in the air photo derived data our data also demonstrate a real departure from simple scaling at much larger magnitudes the cause of which is not de nitively established copyright 2004 john wiley sons ltd

timing and structural controls on gold mineralization at the bogoso gold mine ghana west africa the bogoso gold deposit comprises 20 open pits scattered along 18 km of a major fault zone which separates birimian supergroup turbiditic sedimentary rocks to the northwest from tarkwaian group rocks to the southeast individual pits are centered on 200 to 400 m long ore shoots which are located in three broad structural settings steeply pitching relatively high grade orebodies are commonly localized in left hand dilational jogs in the strike of the controlling faults these jogs often coincide with intersecting minor faults gold is largely confined to the graphitic mylonite which defines the fault and imbricated slices of carbonate altered rock gently dipping mineralized quartz vein stockworks and disseminated auriferous pyrite and arsenopyrite form broader zones between more steeply dipping bounding faults in the vicinity of right hand bends and splays in these faults smaller zones of disseminated sulfide mineralization coincide with areas where bedding and or foliation in the adjacent birimian sedimentary rocks is strongly discordant with the adjacent mineralized fault generally where the faults cut the short limbs of tight upright east trending folds approximately 75 percent of the gold extracted from the bogoso district has been mined from a cluster of pits that coincides with the densest and most highly connected concentration of larger faults in the bogoso concession the majority of ore shoots are located along the largest of these faults the narrower faults generally host smaller and less frequent ore shoots the fault network originated during an early episode of regional scale shortening involving thrusting and isoclinal folding the structural setting and geometry of the ore shoots implies that mineralization occurred during a later minor episode of sinistral strike slip movement on the controlling faults after development of the fault network the undeformed nature of the auriferous sulfides implies that this was the last phase of ductile brittle deformation on the host faults this conclusion is consistent with earlier work indicating that the giant ashanti deposit 150 km along strike from bogoso also developed during a period of small displacement sinistral offset late in the history of the host fault network

effect of forest harvesting on hydrogeomorphic processes in steep terrain of central japan abstract forest harvesting activities affect various hydrogeomorphic processes in forest terrain including increases in occurrence of mass movements i e landslides and debris flows and changes in sediment transport rate in channels thus the influence of harvesting on these processes needs to be assessed to protect aquatic ecosystems in steep terrain with frequent mass movement relationships between rainfall magnitude and frequency of mass movements associated with forest harvesting are needed to develop improved strategies for disaster prevention we examined the effects of forest harvesting on the frequency of mass movements in the steep sanko catchment central japan using aerial photographs for six different years covering 1976 to 2003 we also investigated the spatial distribution of sediment stored in the system as well as sediment transport rate in selected subcatchments by field surveys landslides occur during moderate rainfall events return period of daily rainfall 25 years after harvesting the occurrence of mass movements substantially altered the volume of sediment storage in the channel that links sediment supply from hillslopes with sediment yield downstream however the volume and spatial distribution of sediment deposits in headwater channels were not clearly related to forest age because of the redistribution and evacuation of sediment by debris flows bedload transport rate was highly affected by sediment storage volume whereas suspended sediment concentration was affected by the area of exposed sediment along channels that was carved by debris flows thus the effect of harvesting on hydrogeomorphic processes cannot be estimated simply by the elapsed time after forest harvesting rainfall magnitude and the history of mass movements need to be considered to better understand these linkages